"But seeing they could not See; hearing they could not Hear"
“The views expressed herein are those of the author and do not necessarily represent those of the National Weather Service or affiliate/related organizations. Please consult .gov sites for official information”

"From its chamber comes the whirlwind, and cold from the scattering winds." - Job 37:9.

"The wind blows to the south and turns to the north; round and round it goes, ever returning on its course".

Friday, September 30, 2011

Fall Arrives On Cue After Midnight - With a Severe Storm Possible

A Severe Thunderstorm Was Reported near Mims Yesterday with 1" Diameter Hail
Other Lightning Storms Were Subsequently Generated in part due to outflow from this storm in Osceola County toward SE Polk County well after dark  

TODAY: Confessing first off that I've delayed posting today to see how parameters would materialize with some day time heating. For the most part, not many  surprises from earlier. Today's post is based on model trends (although they do not agree at all), SPC mesoscale analysis which updates every 15 minutes (but based in the upper levels on the RUC model), radar and satellite trends, and bit of gut feeling. In short, the final straw drawn was from the Magic Eight Ball app...which read, "A word of the wises, be prepared for surprises". Although, not sure if that meant "Surprise, no rain anywhere except in one spot... or, Go for the Big Rains over South Florida". I chose neither, but sided a bit to the unreliable NAM of summer and latest trends.

NOW: The first cold front of the fall season is moving through the panhandle as we speak, and seems to be draped from near St. Augustine to Gainesville to north of Cedar Key. Elsewhere, a mid-level trough is pulling off the Central East Coast which was responsible for the activity yesterday with a bubble high having filled in behind it and responsible for the nearly cloud free skies central early today with southern branch high clouds and some developing cumulus over South Florida. The vorticity max with the upper level trough is strengthening since sunrise and the upper level trough is aligning with mid-level features as well as surface features which was thought might occur in yesterday's post. 

Heating of the day should slow the boundary down just a bit as the coolest temperature plunge is still a full 24 hours away. Despite unfavorable moisture levels over South Central Florida , we still might be able to squeeze out a storm or two as the vort max crosses Central Florida by mid-afternoon through sunset into South Central Portions.  Vorticity advection is also increasing as the vort lobe is now much less linear than earlier this morning.  Moisture is being drawn up the immediate east coast toward Canaveral and Titusville and might be enough to pull off a shower today if not a storm near or just off shore. It is tempting to say there will be very few showers if any today, and all will hinge on one or two storms over South Central Florida. If so, any such storm could be severe due to 1" or larger hail or strong wind gusts around 58mph. On the otherhand, will there be a storm at all?!! 

Sea breezes today should be quite light and remain close to US1, but I am watching for the west coast sea breeze to start to move eastward toward North Central behind the front itself during the mid-late afternoon, that could be a key and final ingredient if so. Winds aloft are averaging up through the steering level around 15 kts from the WSW. Thus, storm motion will be zero until one that forms can latch on to the upper level winds at which point deviant motion, more likely toward the South or SSW-SSE is possible.
Bulk shear is increasing to 35kts over Central Florida, and upper level temperatures are cold enough to support hail.

This image shows the Vorticity Max and frontal boundary with it across north Florida moving ESE. The blue circle shows where it is advecting toward. No storms are occurring now because it is over much drier air, but as it enters the area of better moisture a storm could suddenly pop up unexpectedly south of the Beachline after 3-4pm. Red shows  preliminary areas thought for a very strong or severe storm. Bear in mind, any storm will be very isolated, so most people will not see rain today, if any one does for that matter.   
     The final ingredient for a severe storm today is the mid-level moisture gradient along eastern portions of South Central Florida ...although I must say that during the past hour some of that moisture seems to be mixing out with daytime heating, thus the very low confidence in storm formation there. All in all, if I had to narrow down the red area even smaller it would be for one lone storm over  Okeechobee or Southern Osceola County advecting toward or forming another in Southern Brevard toward Palm Bay.

Further south, a problem down in this region is the high level clouds. Those didn't seem to stop one lone storm from forming yesterday though in Palm Beach County near the lake/sea breeze boundary. The parameters over South Florida for severe are not as good other than here lies much more  low level instability, thus more showers could form in this area, but again, moisture here is waning with peak heating approaching. Temperatures aloft here were cool this morning per the MIA sounding, but guidance also shows those were from the overnight boundary in place which is pulling out, so those temperatures might be warmer than the sounding indicated here bu later this afternoon  . 

Thus, isolated showers despite the better moisture and with lack of better upper level support such as bulk shear and vorticity which is over Central until late, as well as less dynamic sea breeze/lake breeze interactions. Not sure sea breezes will be as effective today as much either as much as mid-upper level dynamics, and with light Lake Breezes those too might only play a small role in storm or shower formation. If I had to pick 'somewhere' over South Florida it would be near the East Coast from Central Palm Beach County through Southern Dade toward interior Dade/Broward, with a possible storm or two as well in Martin County or St. Lucie. 

For the most part, most people will not receive rain today, but those that get more than 1/4" will likely to so in the form of a very strong or severe storm.

TONIGHT AFTER 10PM: Storms could still form, or a storm could still be in progress, through 9pm in any of the highlight areas in the image above. The cold front proper will arrive like  'fall clockwork', after midnight on October 1st per last year, with frontal passage in East Central between 1AM and 5AM, and southward to South Florida from daybreak through mid-morning. It should progress toward Central Cuba where it could eventually retrograde back north to the northern portion of the Florida Straits by Monday.

Morning lows will be the coolest north and central than in quite some time, with the magic 67F possible along A1A in Brevard but cooler west of the Banana River. Afternoon highs on Saturday over South Florida should reach the mid-80Fs, but even 80F might be a stretch along and north of the Beach Line with increasing NNW-NW winds during the afternoon. The driest and coolest air will arrive Sunday morning and remain in place until day break Monday when morning lows everywhere will be at their coolest.

The only areas that will escape the very driest of air is far eastern South central and South East Florida and around the tip toward south of Naples. This will allow daytime highs to heat up toward 80-85F South Central and South on Sunday after a very cool start, but also will allow a fairly rapid temperature drop shortly near and during sunset. Overnight lows along the east coast should occur in the middle of the night, although one more very cool morning could occur Monday west of US1 before NNE winds set up.

The next chance of showers near the east coast appears to be on Thursday, with some stratocumulus clouds advecting on shore on Wednesday. The only other thing to watch for during this cool down will be high cirrus clouds over South Florida streaming across from the Southern Gulf. If so, daytime high temperatures will not be as warm as the current line of thinking advertises south of Lake Okeechobee.

This second storm, part of a cluster, was observed near St. Cloud yesterday toward sunset. cloud to ground lightning was intense, but not too frequent. There also appeared to be a funnel cloud (upper left) induced by  wind shear outside of the rain foot  visible on the right side of the image

No comments:

Thursday, September 29, 2011

Very Isolated, Briefly Strong/Late Thunder Central Interior Late

Low that was over the Upper Midwest has opened up as a stronger modified  polar like trough drives ESE kicks it off toward the ENE. The main frontal feature this afternoon will be diving through the mid-sections of the country, while the weak boundary over North Florida washes out over Central During the afternoon/evening
TODAY: The upper level low over / near the Great Lakes is finally opening up to an open wave and being booted ENE-ward as a stronger low pressure trough drives in behind it from the WNW-NW. The two will gradually merge over the weekend and be out of everyone's hair up north by Late Monday (at the latest).

Further south toward Florida, the south half of the state appears to be under the 'general ridgy-ness' at the surface and mid levels that Central Florida was under yesterday as the main frontal feature starts to develop well away to the NW and deepens with time today.   The actual front itself is quite dry (inactive) other than over the more northern tier of states.  Meanwhile, the north half of the state is under general but weak  "troughiness" increasing with time, but it is a slow process. 

Morning  KSC profiles are all showing a developing westerly flow above 5000 ft, although very very light and not of any significance until above 15,000 ft or higher. Thus, steering is close to negligible once again. Further south, an equally light steering from the east is apparent. Southern branch jet stream cirrus are moving in across the south half of the state, mostly south Florida. There is a big break coming for them earlier today, but that might fill in heading toward early afternoon. So , despite the big rain chances reflected by the RUC model especially along their west coast, believe that this moisture might or should be attributed to moisture at non-precipitable levels; thus, South Florida might end up with high level partly to mostly cloudy skies by mid-afternoon, inhibiting further rain shower development beyond what could form toward the east coast with the sea breeze as far north as Martin County.

Further north toward Central/South Central, cirrus will come and go throughout the day, but not be the prevalent mode. Ultimately, storms / showers will form along the east coast sea breeze (very isolated) with a delayed seabreeze north of Sebastian Inlet, namely Brevard County. A heavier shower or thunderstorm is also possible after the 3-4pm time-frame, apparently toward Palm Bay, but that chance is remote.

The heavier activity should occur after 5-6pm toward one hour before sunset west of I-95 along the final sea breeze mergers over Central Orange south Osceola County, and possibly far northern Okeechobee County.  Like yesterday, one storm could form closer to I95 earliest, with a subsequent outflow from it inducing yet another storm further from the coast late. I've noted that the RUC has been insistent that much of the north half of the state remains under convective inhibition until after 2-3pm, although the NAM breaks this down after 2pm, at which point the sea breeze should have penetrated to at least I-95 as the west coast sea breeze will be in full gear toward the east north of Sarasota.

NOTE SHOWN; Showers toward the west coast, but see all the cirrus? Not so sure about that. Also note shown is the remote chance of a shower/storm toward Volusia County or Flagler County.

Further north yet still, believe the northern most extent of any thunder today will be Central Volusia County closer to the coast , but it is still too early to determine if any last minute moisture squeeze with the sea breeze convergence could dish out a shower or thunder that far north. This can only be determined by watching hourly advances as the situation develops, but for now I did not sketch that area in. The latest LDIS plots from KSC/MLB show more moisture in the mid-levels associated with the old boundary than any model guidance does to the north, so it's hard to know exactly which one to believe.

FRIDAY: Very tricky day. It could be either near rain free, or we could once again have a strong storm or two toward the Central/East Side mid-late afternoon. The frontal boundary is forecast by the NAM to become stacked or nearly so at the surface with upper level features during the course of the day. It must be pointed out at this stage that the GFS showed no such chain of events in the last two runs, and actually has the front through..or rather..a preliminary front through..after tonight..with the second one indicated by merely a dry wind-shift...if even that.  The reason for this is because it quickly builds high pressure over the Gulf across the state after sunset tonight, never to again be replaced by the secondary trough on Friday associated with the primary front.  

This is a big shift in 'model reasoning', so will run with persistence of its previous runs as well as that of the morning NAM. (but will say, the GFS has done quite well this summer as a hint to what my gut is thinking).   In which case, moisture convergence ahead of the boundary which will be aligned NNE-SSW across NW Florida toward JAX late in the day should result in a similar set up as today, but with slightly cold air well aloft. It may be that Friday will be completely rain free, but as noted, will ride with previous persistence for now.  Any rain tomorrow with the front will be over Central or South Central Florida, and South Florida could be close to rain free other than showers like today  .


Timing is still tricky as usual in regard to exactly WHEN the front will cross the peninsula in full. A mix of the previous GFS and latest NAM dictates the front to go through overnight Friday night and clearing the entire state by mid-morning Saturday if not sooner. It could be accompanied by a stray shower near the coast of Brevard, but otherwise frontal passage itself elsewhere will be uneventful due to the timing of its passage with overall low moisture accompanying it.

The driest air associated with the front, as well as the coolest air, will be limited to west of I95/US1 zone from the Beach Line toward Sarasota (typical). As such, the coldest mornings Saturday through Tuesday will be in those areas, with the coolest afternoons Saturday/Monday. South Florida will never really get into the driest of air nor will the far east coast of Brevard and South. Winds on Saturday should be NNW-NW under sunny skies making for a very pleasant day with highs in the low 80Fs for a brief time, with near 79F being the prevalent temperature.  During the night heading toward Sunday, if the front does go through as it now appears it will, winds could become North to NNE by daybreak Sunday, which for Port Canaveral and South is slightly onshore...and again, will prevent this area from cooling down over night.  This is not for all certain though, so maybe East Central (COASTAL) Brevard will reach the magic 67F Degrees Sunday morning, as is often the case time and time again with the first front of the year from my experience. 

Interior areas as far south as Okeechobee and closer toward the SW coast could also be quite cool, with the areas near Ft. Myers all in all being cooler that much further north and east toward Coastal Brevard. The coldest of all will be the Panhandle and east to Gainesville and south to Ocala, where overnight lows could reach the mid-40Fs over the west half of the panhandle and near 50F toward Ocala.

MODIFICATION BEGINS SLOWLY ON TUESDAY with a small chance of coastal low topped showers, east of I95 from Brevard and north to Jax by overnight Wednesday into Thursday with continuing, never-ending ENE-NE winds gradually becoming more easterly by next weekend. It will be a slow process as the high pressure area behind this front will get locked in place over the eastern Mid-Atlantic states all of next week and beyond. In other words...CURSE OF THE FALL EASTERLIES WHICH SEEM TO GO ON FOR A LIFETIME ensues for the entire state well into mid-October.  

No comments:

Wednesday, September 28, 2011

Better Chance For Very Isolated Showers/Thunder Today

TODAY: There is much less over all atmospheric moisture availability today state wide as opposed to yesterday, on the other-hand, high cirrus clouds which moved in yesterday that likely capped off the rain chances to very low do not appear will be a problem today across Central Florida; however, they do appear to  be encroaching into SW toward all of South Florida as of 1pm. Already, developing cumulus cloud fields over SW Florida have dissipated (for the time being) in that area, whereas showers have formed along the east coast sea breeze.

This post today is a blend of the RUC and latest 8AM GFS. The RUC has been ADAMANT at nearly scattered thunderstorms this afternoon across all of Central Florida into South Florida, this is due to vorticity at the low through upper levels that it presents. However, no such feature (s) is apparent, so will downplay to isolated activity due to low atmospheric moisture with not boundaries. A ridge axis from the North Central Gulf extend across Central Florida, whereas another ridge axis does the same from the Atlantic. Storm/shower motion should be toward the SSW/SW but be quite slow to negligible since activity should not move far from where it forms.  Showers/storms should wane quickly with the setting sun, although there could be a few showers or small storms over the interior until just after sunset. The more dominant feature will be a stationary boundary along the northern Gulf Coast from Louisiana through the Florida Panhandle extending toward JAX, where a more prominent storm could from West of the St. Johns in northeast Florida, with more activity along the western Panhandle.

THURSDAY: The upper low over the Great Lakes will be on the move late today very slowly toward the East as a more powerfully progressive trough tracks across Southern Canada. As the large low moves east the boundary over North Florida will wash out into Central Florida on Thursday, with a slightly better chance of showers/thunder over the NE quadrant of the state, namely from Brevard County toward Ocala/Gainesville/Jax triad. South Florida will have a day similar to today with mainly showers along the sea breezes, and maybe an isolated thunder chance.

FRIDAY: The upper low over the Great Lakes will move east and relax into an open wave/ trough while the secondary, more powerfully progressive trough drives ESE-SE into the Great Lakes to replace where the former one had been stationary. As the two systems merge a more organized cold front will form Thursday night which will drive into the Mississippi River Valley and  the Deep South Thursday night into Friday. Like on Thursday, this boundary will be located across Central Florida on Friday during peak heating, with the better chance of storms associated with it over Dead Central, favoring the east side from early afternoon through sunset. Moisture still isn't all the greatest, but colder air aloft in the mid-upper levels should help negate the lack of overall moisture, which should converge along and ahead of the boundary under the cold air aloft and continued high temperatures near 90F at the surface. Some of this activity could be quite active into Sunset Friday night mainly along central Florida from Daytona Beach toward Vero, with other showers further south along the east coast...but again, it will be isolated in nature. 

SATURDAY: So far, timing has the actual frontal boundary driving through the state after sunset Friday night through mid-day Saturday, perhaps even faster after dark. Northerly winds should be in place for all of the state Saturday afternoon accompanied by near clear skies and temperatures Saturday afternoon in the low 80Fs to upper 70Fs far north Florida.  Overnight Saturday night high pressure builds in quickly across the southern tier of states and winds become more NE-ENE during the day Sunday, strongest across far South Florida and the keys.  

SUNDAY/TUESDAY: The only favorable location for rain showers/thunder will be across the Far Southern tip of the state from Southern Dade County and through the Keys, including Key Largo.

During the course of this first frontal passage, which coincidentally is forecast to occur on the exact same date as last year, October 1st, morning lows along the east coast will be close to 70F and highs will be in the low to mid 80Fs, with some upper 40s to mid-50Fs mostly around the Big Bend and all of the panhandle. By Tuesday east coast temperatures will essentially be equal to the ocean temperature near shore, or just a bit below that by noon time, with only about a 10F degree variation in the temperature fields between morning lows and afternoon high temperatures. So far, it does not look as likely that a major rain event, or any event, will be in the works as opposed to earlier model runs, but this will need to be watched for as the time approaches (by Wednesday), when such a set up would be more likely as winds become more due easterly.

No comments:

Tuesday, September 27, 2011

Recycling Day As Deepest Moisture Moves Out and New Troughs Move InBi

Low Rotates Back toward It's origin - Lake Michigan - toward Wednesday as occluded (purple) front wraps around it. Another stationary front runs out ahead of it, and the old mid level boundary that was over North Florida sinks and stretches out more NNE- SSW down Florida. The pressure pattern over the Atlantic is breaking down 

SYNOPSIS: The large upper low over Illinois is slowly moving toward the east to ENE today but will make little progress. Meanwhile, there appears to be a mid-level trough axis running down the east side of the State this morning, and latest RUC forecast shows very little displacement of it during heating of the day, likely due to a thermal low level trough being established across the interior with heating of the day down the spine of the state. The deepest moisture is along the east coast from Brevard and south. South Florida had the most moisture this morning, but it appears as though since the time of their sounding at 8AM it could have lowered further. In all, the deep moisture of days past is moving out along with yesterday's cloud cover. 

The large low over the upper MidWest will move east to ENE through Thursday as a series of vort lobes and surface boundaries continue to dig deeper into the eastern and SE states through Friday. Another low pressure trough moving across Southern Canada is expected to push the first low out of the picture, at last, but re-establishment another deep upper level trough near the same location by Friday as the first one which finally also press east through the weekend. 

 During this course of events, Florida has lost its deep tropical moisture connection (air mass), so most moisture for storms will rely on the ever critical location of surface/mid level boundaries where winds converge to enhance localized deeper moisture such as along Lake/Sea Breezes and mid-level troughs. This could be an ongoing theme through Friday, with the rain chances diminishing to near zero for north Florida (mainly the panhandle region) on Thursday.

TODAY:  As usual, transitional periods are tricky at best, especially now that we have lost the deep tropical connection and an apparent mid-level trough axis is elongated down the state;  in short, we have an entirely new 'ball game' to play. 

SW Flow seems to be the consensus along the east side of the state, albeit quite light. However, as of 12:30pm the ECSB has yet to set up, so the RUC/GFS might just have something there with their propositions of a delayed or at least east coast sea breeze until mid-afternoon . The hamartia for forecast busting today will be just exactly where deeper moisture can re-establishment as a result of moisture convergence as opposed to the free flowing moisture of the past few days.

Showers have already formed near Lake Okeechobee, as residual pockets of fog and low clouds continue to burn off elsewhere.  The most unstable atmosphere is along the west coast near TPA and north, and this should move inland during the day across most of the north 1/2 of the state. However, this area is also most dry atmospherically speaking.  Sea breeze circulations might not set up in full until mid-afternoon, if not later north of Lake Okeechobee. Meanwhile, a jet stream speed max is apparent coming across the Gulf in model guidance and satellite imagery.

MAIN FACTORS TODAY: Deepest moisture along the east side and convergence along mid-level boundary (blue) highest instability advects  eastward toward the east from the Gulf, combining with divergence well aloft associated with a jet stream speed max at 30-35,000 ft of 60-70kts. Stronger storms near the Lake and interior North Central to NE Florida.
There could end up being highest coverage due to outflows from north and south over Osceola County by tonight.
THUS, for today more thunder as opposed to rain showers, but all in all should remain fairly isolated, although there could become a time of better rain coverage by early evening over the interior spreading toward the east coast and offshore, especially along and south of SR 46. Thus, today, like all the others could end up cloudy in many locations along the east side by sunset.  South Florida as always should kick off soonest, but the strongest storms will wait for possible sea breeze convergence underneath the mid level trough axis where the deepest moisture resides, which would be further north. The coldest air aloft is near I-4 and north, but only by a very small margin. The strongest storms , although more isolated should be near NE Lake County, Seminole, West Volusia, Flagler, and western St. Johns counties..with another stronger storm or two in St Lucie/Marian Counties and maybe Southern Brevard/Vero area. The strongest storms will result from where two or more boundaries meet late in the day..somewhere along the east side of the state or the interior. Greatest coverage of rainfall does not equate to where the strongest storms will be.

Not meant to be 'all inclusive' because thunder could occur near the east coast anywhere over South Florida to DAB, but the greater concentration should be a little away from the coasts. Although not shown, Osceola County through Orange counties and north could end up with bigger rainfall totals due to training or slow motion of heavier rains after 5pm. There could be a 'cluster' of moderate rain to move offshore tonight somewhere along the east coast almost anywhere, most likely north of Lake Okeechobee.
WEDNESDAY/FRIDAY: Late Friday or  Saturday could be fall's climacteric, if for only a day or two..more so for the northern 1/3 of the state. Expecting that local forecasts will go up and down on rain chances up until that time due to the uncertainty of where boundaries will be found until the final blow, or front, can press south. As of the 2AM GFS, that would occur Friday night, with the front over or near the Florida Straits by Saturday afternoon. Before that time, thunder is possible..and if timed just right per the GFS early today, would be across Central Florida during peak heating on Friday. Thus, some stronger storms (isolated) could occur this day in that location. The front has yet to be forecast to cleanly clear the Florida Keys, so rain chances might actually pick up in that location over the weekend. 

With the frontal passage, whenever that might be, the east coast could expect a 'fall like' morning in the temperature department, but with the progressive southern tier of states pattern in place abetted by the southern branch jet stream, it will be short lived as onshore flow ensues within 24 hours after fropa if not sooner (frontal passage).

NEXT WEEK: We could be setting up for an east coast rain event, most likely south of SR 50 and north of Ft Lauderdale by the middle of next week. The most likely area would be Palm Beach County upstream of the onshore flow off the Bahamas, with the Ft. Pierce area coming in a close second as a contender. Other areas south of I-4 might get in on the act in-part. ..put rain chances do pick up again over South Florida at least  due to the lagging   mid-level frontal boundary. 

 In the longer term, a much deeper full latitudinal trough of threatening proportions is forecast to develop in the country's mid section toward next weekend as we progress through the first week of October. Not shown yet, but there is a chance that too will cut off neat the Great Lakes, or could be a severe weather maker at various stages of its frontal life cycle stage from the Central Plains toward the Ohio River Valley and portions of the SE states in the great beyond.      

No comments:

Monday, September 26, 2011

Numerous Showers and Isolated Thunder Possible Today from Noon through 9pm

TUTT low continues east of the Bahamas with a high to its north. This blocking pattern is one factor that is preventing the low over N. Illinois from moving through the past few days until  at least the first 1/2 of Wednesday. Weak boundary from the Gulf to the panhandle is washing out this morning. Cold front/trough over Ohio Valley will press east to the north but its southern tail end will only sag south slowly with time.

SYNOPSIS: Upper low remains in place as expected awaiting a 'kicker'. Blocking pattern over the western Atlantic continues to stagnate the upper level pattern from progressing. More active stormy areas over the Ohio and Mississippi River Valleys in a few areas today, while Florida and the East coast to North Carolina continue to bathe in a high moisture content atmosphere. This same pattern, with a little drying in the atmosphere will continue on Tuesday with much less activity, although isolated storms are still possible over Florida.

TODAY: Latest SPC MesoAnal shows surface vorticity running up and near the SE coast and  the Gulf Stream. Flow aloft at the steering level remains weak, but latest KSC sounding and area profiles show a steady SSE-S Flow at 10-18kts from 2000 - 7000ft running up the east coast...nearly parallel to the coast to just a bit of an offshore component north of Ft Pierce. Otherwise, abumdant cloud cover exists across the South Half of the state under divergent flow aloft at the jet stream level. Abundant moisture and moderately unstable mid-level air might serve to continue cloud cover over the southern 1/3 to 1/2 of the state as opposed to rain/storms with some heating, OR..heating might serve to break the cloud cover up. However, thunderstorm activity along the SW coast is spreading anvil debris across the region south of Lake Okeechobee, so thunder might be hard to come by in that area except toward the East Coast where it will be last to arrive. Either way, convergence near the coast in SE Florida could generate some good rainfall totals. That area is also first to become less inundated with convective inhibition as seems to always be the case, but the remainder of the state should follow suit by 11am to noon. The least cloud cover will be north of the Beach line toward Sarasota and up toward Jax.

Sea breezes might be a bit delayed due to the cloud cover, but are more definitely expected by 2 pm from the SSE or nearly 'upriver', with winds just above that level almost due south and weak steering above that under divergent flow aloft. The atmosohere will become most unstable where there is less cloud cover, namely from Brevard County and west toward Sarasota and north toward Ocala/Jax/Gainesville.

Showers could form along the Treasure Coast, and if the pattern which was set in place very late yesterday holds, which seems to be the case this morning, activity could move right up the intracoastal to just offshore into Brevard County and the interior.

Once the sea breeze is more solidly set, the stronger storms should end up north of the Beachline along convergence of that wind with the prevalent South wind just above the surface along and west of US1 and amass in the most unstable atmosphere over North Central toward NE Florida, with strongest storms toward Ocala/Gainesville/Jax areas with other storms closer to the coast of Flagler and Central to northern Volusia Counties later in the day toward 5-6pm and beyond.  All of the above might be able to occur regardless of cloud cover. That will be 'the bugger' for today regarding coverage amount, location, and intensity, but still believe it will be the northern more areas with the stronger storms.

Further south toward Central, other most isolated storms west of US1 or I-95 could also develop late, after 4-5pm with the sea breeze merger and be advected and propagated toward the NNE. Showers and thunder might be able to generate late as well toward South Florida given there might be time for this area to clear out, assuming the activity along the SW coast dies out and allows some clearing, although by later this area might be either completely worked over or too cloudy for storms to generate. 


TUESDAY/THURSDAY: It appears as of early this morning that moisture will begin to wane on Tuesday, but only to the degree to limit extensive cloud coverage but not enough to prevent rain and storm formation. There might be a brief 'drying out' period across Central on Tuesday, but as we work toward the Wednesday through Friday time frame that secondary frontal boundary, albeit washed out, will move into Central Florida where it is then possible it will wash out during Friday toward South Florida by Friday. During this time, sea breeze convergence and much colder upper level temperatures could result in more isolated but stonger thunderstorms, most likely somewhere across Central portions. This is a new outcome portrayed by the 2AM run of the GFS, of which reliability out toward Thursday starts to become more uncertain, but is worth monitoring.

No comments:

Sunday, September 25, 2011

Isolated Thunderstorms East/Sct'd West - Some Strong Late

Active Shortwave trough has developed on the SW Corner of Cut off,quasi-stationary upper level cold core low over Western Illinois. The low itself has retrograded to a small degree in 48 hours toward the SW from Lake Michigan. Strong/severe storms possible along that S/W trough. Pressure gradient aloft over Florida is relaxing due to the now even greater distance from Florida, although minute, effective. TUTT low north of the Dominican Republic and High Pressure over the Atlantic producing sinking motion over a layer of shallow , moist air over the Atlantic east of the Gulf Stream. Disturbance, likely enhanced by the Gulf Stream east of Florida is advecting toward North Carolina Coast today
THE BIG PICTURE, SYNOPSIS: The upper level, cold core low over Lake Michigan yesterday (which resulted in a number of waterspouts due to the warmer lake waters and very cold air aloft) has retrograded into West Central Illinois. This depiction was indicated by some of the models yesterday to occur. Meanwhile, a frontal boundary has evolved arcross Arkansas into Southern Illinois, which will gradually wrap into the parent low pressure system tonight and become a part of the occluded boundary further north.

Further South, as a result of the upper low retrograding, the pressure gradient aloft has weakened as if it wasn't weak enough already the past two days, although the overall 'troughing' is digging deeper into the Northern Gulf to the west of the state. Showers have erupted as result over the Gulf and are moving across Coastal SW and West Central Florida at noon time, with additional showers along the east coast. Otherwise, moisture amounts remain high at 2.00+" universally, which is well above the norm for this time of year, as sensed by the muggy conditions outside. Instability is highest just off shore the Cape to JAX with most areas fairly uniform in that department. 

There seems to be a bit of mid-level drying late this morning along the east half of the state north of Lake Okeechobee, possibly due to some subsidence on the backside of the offshore trough.

 As a result, cumulus cloud lines forming along the intracoastal are not gaining as much height as they would otherwise. SW Steering toward the NE seems much stronger in satellite animations on the west side of the state, but dwindles to  nearly neutral in the interior and east side.  Otherwise, conditions would be favorable for waterspouts along the east coast through 2pm, but so far that possibility seems all but naught due to slightly drier layer aloft, as observed by the downdraft CAPE portrayed on  the SPC mesoanalysis page selection for that parameter.

Latest Mesoscale Analysis from the SPC website shows Downdraft CAPE on the east side of the state. This parameter is a good indicator for strong winds in thunderstorms in downdrafts, but is also an indicator depending on other parameters that storms might have a hard time getting started without a trigger, of which in the case of today there does not appear to be one other than lake and sea breeze mergers. 
TODAY: Activity should have no problem initiating as already observed from SE Florida and up the west coast. However, the further North and East one goes, so does the steering currents weaken to almost zero in the area of downdraft Cape. That factor, combined with the presence of some drier air aloft should inhibit thunderstorm (showers still possible though along the sea breeze) development through early-mid afternoon along the east coast except perhaps toward Lake Okeechobee/Martin/St. Lucie/Interior Palm Beach Counties. Showers are already becoming scattered South, but thunder remains isolated,  and with temperatures aloft no different than yesterday expect that persistence should rule the roost today. 

Thus, like the past two days, despite forecasts of model guidance and numerical guidance for scattered thunderstorms, that has yet to be the case. Thus, persistence seems the most appropriate approach until proven otherwise. 

It should be noted that the Mesoscale analysis page for parameters aloft is only as good as atmospheric soundings taken every 12 hours across the state at TPA/MIA/XMR  (KSC)/TLH/JAX/and EVW (Key West). Otherwise, the parameters portrayed are based largely on, you guessed it, a Model (the RUC). Thus, any inconsistencies with the RUC model are reflected in graphics such as that above. I have seen values vary considerably over a 3 hour window of time, but as of early this morning the downdraft CAPE has done nothing but that seems to be the trend for the first 1/2 of the day at least. Note how all the showers on this radar over lay (above) are occurring where there is no down draft CAPE.

THIS AFTERNOON: Sea breezes will set up along both coasts. The east coast sea breeze combined with a lake breeze (Lake Okeechobee) could trigger a strong storm or series of propagating storms either to the north or south toward the East Side of the Lake with lightning and wind gusts being the main danger factors, although a funnel cloud or even landspout could occur with any of that activity as well.

Elsewhere, showers/Storms will form over the SW/W side of the state along the incoming west coast sea breeze. Showers and a few thunderstorms could form anywhere over South Florida and move very little. Again, propagation along the sea breeze and lake breeze boundaries, as well as shower/storm outflow boundaries, will dictate the erratic storm motions in South Florida.

Further north, any activity along Lake Okeechobee could send outflow northward in the very light steering which nearly parallels the coast today, which too can work north with time along the east coast sea breeze. 

However, by that time the sea breeze could be well west of I95 north of Vero Beach or Ft. Pierce. There is one big question though concerning this one tiny but important factor. 

That being, SW to NE steering might increase later today as the shortwave over Arkansas digs deeper toward Northern Louisiana. Granted , that is a long way away, but there is a domino affect which could translate east and south with time. As of now, it appears that will be the case on Monday with all things else remaining the same with the upper low still in place in generally the same location...including moisture over Florida...storms might be more active along the East Coast sea breeze. It is worth noting though with cut off lows, the models as has been cited time and time again, inevitably try to move them out too quickly. 

Thus, Monday/Tuesday's forecast despite what morning guidance reads (which has not all come out yet), could easily be incorrect when it comes down to the finer, more critical factors in the rain bucket department. Thus, I didn't bother waiting for it to become available, it has proven worthless.

Best Guess at this point today. Realizing for most of these early in the day forecasts one has to second guess the model guidance and remain one step ahead of what they actually show, one must project and a bit of a 'means of experience'.  Afterall, ccording to the RUC,   showers  would already be in progress around the Space Center. Not going to happen any time soon...with nearly clear skies at noon.

Showers/storms/and outflows should spread west and north with time, eventually meeting up with the east coast sea breeze west of I-95 (if not further west) after 3pm, and perhaps much later.

The other problem at this time of year is that during peak heating some of the low level moisture mixes out in the absence of any convective inhibition which is the case right now. Thus, the storms do not really 'jack up' until the sun gets low in the sky and dewpoint depressions can lower, or rather, the ambient outside air temperature can lower to meet the dew points. Thus, the most strong activity outside of near Lake Okeechobee and maybe a storm or two over South Florida will be delayed until after 4-5pm...perhaps later. 

Outflows both from the west coast and up the east coast (toward extreme SW Brevard and Osceola County) will possibly foster more outflows to drive the east coast sea breeze further yet inland.

Peak of the strongest activity should be toward Northern Interior as was the case the past 3 days (there's that word 'persistence' again), in or near locations since as the Ocala National Forest where dew-point depressions recover the quickest due to all the vegetation there), and toward Gainesville. Upper level steering should be a bit stronger further north as well, so although not expecting a big coverage of thunder, it could be strong.

The least  chance of seeing rain today will be far East Central, however, with the steering potentially increasing very late today into tonight  combined with remaining boundaries around ..with the factor that the east coast sea breeze will be easing off and and dissolving , some showers/inland storm debris light rains/or even a thunderstorm could impact the near coastal areas near Rockledge/Titusville/Palm Bay and north toward DAB near or after dark through 10-11pm. Very isolated.

TUESDAY: This now seems to be the better day for the East Coast anywhere to receive rain. But then again, that was what the case was previously thought to be for yesterday and today.

BEYOND: High pressure is thought to build eastward behind the shortwave trough toward Florida, putting much of the state in sinking, more northerly component steering ahead of it, and also squeezing out atmospheric moisture, thus lower rain chances. We will have to see if this actually comes to fruition though, since much will depend on the unreliable motion of the already noted hard to forecast Cold Core Cut Off Low over the upper Midwest. The trend has been for decreasing rain chances through Friday after Monday, with little change in temperatures, although inland highs might not be quite as warm. I'm hedging toward keeping better rain chances for Tuesday at this point.

It appears that either solely South Florida or there and South Central will have the best chances of rain by next weekend, mostly showers with a deep , persistent onshore flow, thunder toward the west side.

There are no tropical threats with the two storms well out in the Atlantic. There is a trough now half way between the U.S. and Africa which could pick up Phillip, and Ophelia is having a  hard time with the TUTT low and high pressure north and ahead of it, which is creating shear winds against that system.    

No comments:

Saturday, September 24, 2011

Summer Like Rain/Thunder Chances Continue Through Monday

DESCRIPTION OF THIS IMAGE IS IN THE TEXT BELOW: Key features for the next few days are  a TuTT low SE of the Bahamas to lift NW-N, Closed Low over Lake Michigan/Illinois, High Pressure in the Western Atlantic East of the mid-Atlantic States , Strong Upper Low approaching the Pacific NW, and  the Southern Branch subtropical jet from the Baja to the Northern gulf, and lastly an area of low pressure in the Central Gulf (not shown above).  

SYNOPTIC SCALE PICTURE Through Monday (Above/Below): As noted yesterday, there is a weak area of elongated low pressure near/over the Bahamas. As expected, that region is circulating around strong high pressure to its north and east in the western Atlantic. Also of note is a strong TUTT (Tropical Upper Level Tropospheric Trough) to the east of  that area of low pressure and SE of Ophelia. Both features are tearing away at Opehilia. 

Meanwhile, the closed off Mid-Upper low complex continues near Lake Michigan and will continue in generally  over the same area until another system approaches the Pacific NW and Western Canada (blue arrows). Until that system moves east the low over the upper mid-West will remain in place. 

This is for the Monday time frame at the jet stream level or around 25,000 feet aloft. Again, we see the TUTT low circulation now east of Florida with the low STILL near Lake Michigan. Also, when looking toward Washington state, we see strong jet stream level wind pressing over the coast associated with the Pacific Express. These are supposed to continue east during early week and pick up that cut off low.  Meanwhile, note that trough (in black) lagging well behind to the WSW of the  low over Illinois. This trough will slide east and south through late week, thus, southern branch jet stream winds continue over the Gulf and increase a bit over the peninsula of Florida. 

Again, this is only in the upper levels. In the mid levels (not shown) is an inverted trough that extends from a weak low pressure circulation in the central Gulf and across Florida. That will be the key to the weather across the state through at least Monday.

TODAY'S ACTIVITIES: Today there is the area of elongated low pressure to the east of Florida. Showers/Storms are on the east side of the trough axis, far removed from the state. However, as far away as it may be, outflows from storms might need to be watched later today that might approach the coast, but not actually reach it. These could act as moisture convergence points for coastal regions to just offshore.

Otherwise, the main focus today for storms will be the elongated low-mid level trough axis extending from the Gulf of Mexico. This low pressure area is being enhanced by slight divergence aloft from the sub-tropical jet, although there is not a whole lot of storm activity associated with it at this point today. The areas to watch due to the presence of that boundary is the same area as the past two days, Gainesville toward Ocala and South toward Western Volusia/Flagler Counties, sinking south with time toward Sanford/Orlando and the Beachline. At the lower levels, the trough axis appears to actually be across the Beach Line corridor toward Tampa Bay.

The red lines denote trough axis' near the surface. Note the focal point across Lake County toward Volusia County. The other trough axis runs along the Gulf Stream off the Florida East Coast. The actual mid level feature discussed above is further to the east than this.

This can all be seen more easily by looking at the enhanced water vapor image, courtesy of (below):

Extensive drying in the mid-upper levels (in oranges) over the Panhandle in anticyclonic high pressure circulation is visible over the Panhandle with increased moisture further south over the peninsula. The gradient from drier to moist air is near the inverted trough axis. That gradient could serve to foster some stronger storms later today. There is a bit of a moisture squeeze play ahead of the TUTT low combined with the area of low pressure east of Florida, combined with an area of low pressure over the Central Gulf.  This will continue through Sunday and much of Monday for peninsular Florida.

The deepest moisture resides over  Southeast Florida, but plentiful enough moisture is available elsewhere. At this hour of 10AM, much of Central and North Central Florida remains stable due to the late night activity of yesterday. South Florida is already uncapped with showers forming along the SW coast and progressing slowly toward the ENE. Thus, earliest activity today will be over South Florida with showers and thunderstorms, some more lightning prone activity could form around Lake Okeechobee and drift through Palm Beach County and Martin County. Sea breeze convergence could occur over the Everglades and into Western Dade/Broward. Steering is from the WSW over this region south of the inverted trough, but is quite light at only around 10mph at most, so storm motions could be over come by outflows and sea breeze interactions making for chaotic storm motion once the area starts to fill in a bit. We'll also have to watch activity well to the east of the state, since outflows from that activity could converge toward the southeast coast, beginning toward SE Florida then progressing northward later today.

Quick Picture of what COULD evolve today: Thunder, mainly interior South Florida but working toward the east.  

Later activity toward North Florida but having much less motion close to the inverted trough axis where steering becomes light. Stronger winds aloft could generate more lightning prone storms, with outflows working south along either the west or east coast sea breezes, all within a weak cyclonic circulation surrounding the inverted trough in the mid-levels.

 All in all, the heaviest concentration of rainfall lasting latest should be over East Central Florida west of I-95 (much like yesterday) where the atmosphere is most capped this morning. Due to 'anticipated' later storm onset (in general), this area will have more time to destabilize through the length of peak heating as outflows from activity further north and south close in on that unstable zone just south of the trough axis. 

Storms appear most likely to reach the beaches over SE Florida and less so north of Vero Beach where steering is almost non-existent. Thus, the sea breeze collision over the far interior will not affect the coasts until that activity can send subsequently  propogating outflows toward the east  and against the prevailing sea breeze.  

As always at this time of faded summer, much depends today on which sea breeze (if either) is most dominant, or progresses inland the fastest inregard to where a collision  of both will occur. Using the 2-3 day rule (my personal one), today should end up much like yesterday over Central Florida as well as the area more toward the North, although it does not look like coastal Volusia/Flagler will see nearly as much activity at  or near the beach zones as was the case yesterday, or if so, not as early in the day . South Florida should see the biggest change today in regard to the amount of activity since it has been pretty quiet in this area the past several days. 

SUNDAY/MONDAY: These two days seem to be the ones that the immediate East Coast will actually get in on the storm activity, especially once the TUTT low moves north of the latitude of Central Florida which will allow a slightly stronger SW flow aloft to take hold. However, it will be an overall drier atmosphere by Monday, but sea breeze convergence should make up for that difference.

BEYOND: Finally the low over the Great Lakes gets the boot (or so it seems as of this morning based on model agreement and their trends). In doing so, the surface frontal feature washes out before reaching the state as high pressure builds in behind in. Thus, winds eventually amass a more ENE-E component at the lower levels. 

 <In regard to temperatures, there is no cold or cool air invasion. Just a modification as winds gain a more easterly component, meaning over night lows in the upper 70Fs near the coast and afternoon highs in the mid-upper 80Fs (in the interior).>

However, as noted in the top image there will be that lagging upper level trough,  thus winds well over ahead remain from the west. These winds could merge with the inverted trough axis later next week. This will be a 2-3 day metamorphosis during which time rain chances remain, but of more isolated nature. By late next though, the latest GFS has a bit of a deformation zone setting up across Central Florida which could result in increasing rain chances once again over Central and South Florida by Friday. Initially, the GFS showed the deepest moisture to be over South Central and South Florida, but the last two runs are  shifting the deeper moisture a bit more north to include Central Florida with the area along and north of I-4 still in the much drier air mass. Again though, older runs or more recent runs, this time frame is much too far out in time for confidence to be in either case  on the low side, realizing we are now talking about the end of the first week of October.

Time will tell. 

No comments:

Friday, September 23, 2011

July Like Conditions Return On the First Day of Fall

Although anticrepuscular rays appear to converge onto a point opposite the sun, the convergence is actually an illusion. The rays are in fact (almost) parallel, and the apparent convergence is to the vanishing point at infinity.  Anticrepuscular rays are near-parallel, but appear to converge at the antisolar point because of linear perspective. Anticrepuscular rays are most frequently visible near sunrise or sunset. These were observed this morning, but were seen a few other mornings this week just before and during sunrise.

And at the same time as the above image, this storm was over the ocean. Looking toward Canaveral AFS, seaside.

TODAY: Today is the first full day of fall, as of 5:05AM. That might be true in regard to how the earth is aligned with, and rotating around, the sun; but the weather today looks much more like that characterized by a mid-July day. One with plentiful moisture and little to no synoptic scale boundaries. It won't be quite as hot as it is in July, but otherwise all things appear to be equal. And like in mid-summer, outlining any specifically higher potential areas for rainfall is difficult other than the blanket, all inclusive "all over the interior" stand-by.

As of 1pm , the sea breezes have begun per visible satellite imagery. Some showers were ignited earlier due to an outflow boundary off the NE coast in the Flagler County area which moved ashore in that region, but otherwise showers are few and far between. Moisture content today is high (2.00" +), and once moisture convergence begins as the sea breezes approach each other it will be even higher. Steering today is weak, but generally from the WSW-SW at 10mph or less, and apparently restricted to the north half of the state. Toward Lake Okeechobee and South into the Everglades currents are less than 5mph. Showers should start to begin well before the sea breezes meet, but most prolifically after 3:30-4pm. A few more lightning prone storms could form before and during that time, but have the greatest overall coverage and strength after 4pm -6pm.

Ocean showers were lacking this morning other than right over the coast of Central and North Brevard, since steering is no longer bringing them ashore north of Palm Beach County. A few formed within two hours of sunrise, and one was easily visible a full hour before sunrise as the first rays breached the horizon and lit the top of this tall shower under otherwise nearly full-dark conditions still in place while the moon and stars were quite visible even still...

Fairly uniform distribution of moisture and instability with weak steering, especially over the Southern 1/3 to 1/2 of the state. Further north toward Brevard, showers or storm debris could move offshore toward early evening, and perhaps a series of storms/outflows could back build to US1 after 5:30pm, and maybe move offshore north of the Beachline or just maybe as far south as Sebastian Inlet.
 Like most July days, the bulk of activity today will be over the interior, but visible from the coast albeit at a "not so far away' distance. It looks like there should be a good coverage of activity today, and like yesterday some storms could contain considerable amounts of dangerous lightning activity and very heavy rain. With slow storm motion, and with rains likely impacting some of the same areas impacted yesterday, localized street nuisance flooding/puddling is possible. Rains were quite heavy yesterday over the interior at some locations, and some areas received heavy rain more than once. 

Rain so heavy it looks 'bluish'. Note how lush the interior swamp lands are now after a full summer of storms.

Strong storms are not anticipated in regard to winds/hail, but if so would be most likely to occur toward the far north where slightly colder temperatures aloft might exist later today.. the strongest storms will likely occur due isolated/localized mesoscale boundary interactions.  

Storms/showers/remaining light rain pockets could continue in the chosen select areas until 10pm tonight, if not later. The rains today when all is said and done will favor more toward the east side of the state, but most anywhere 10-20 miles away from the immediate coasts could see rain today. The least likely area appears will be over the Western Panhandle, but there too, a strong storm or two could occur but of more isolated nature.

SATURDAY/SUNDAY: So far it appears nothing significant enough beyond what has been written for two days now has changed. Thus, more July like weather. Activity could start a bit earlier on is interesting to be watching this (below):

This area of disturbed weather  has no apparent surface lows, or any lows really although some guidance points to weak cyclonic circulations in the mid-upper levels here and there. Overall, this appears to be deep moisture being rotated around the western and southern periphery of high pressure that extends well out into the Atlantic.  The activity is propagating generally in the direction of the yellow arrows. Even though this is not a 'system', some of the moisture associated with this activity could come in to play over the weekend for at least the South half of the state.
 MONDAY/BEYOND: There is a nearly cutoff low pressure system, quite large, parked over Illinois. This area is quite expansive and Florida is just barely receiving some the mid level circulation around it (hence, the light WSW steering currents in the mid-levels). The surface front from it is almost completely wrapped around the low, but a weak lee side trough has popped up from time to time down the Appalachians, with a more well defined boundary tracking south then almost due west in the Southern Plains.

Most guidance has leaned toward filling the low and lifting it out toward the NE on Monday, while the frontal boundary gradually drops south and east with time into the far Deep South and into the Panhandle of Florida by Tuesday. At that point and beyond it becomes nearly indiscernible and dislocated from the parent low pressure area now very far away,  as nothing more than a gradual change in wind direction and atmospheric drying. 

Thus, by Monday rain chances might be restricted to the Southern Half of the state, but not entirely. There has consistently been a drying out period portrayed, but much will depend on where the boundary ends up over the state (assuming it washes out over the state). Wherever it ends up will end up being a focusing mechanism for moisture convergence so that despite lowered overall atmospheric moisture being infiltrated into the state due to the loss of the tropical connection, there could still be showers and thunder somewhere, apparently the whole way into next weekend. So far, Tuesday seems to be the most quiet day other than the far South and the Panhandle (where the front will reside at that time). The morning GFS of 2AM has the boundary washing out over Central Florida heading into mid-week next week as high pressure moves in to the north and easterly flow returns, but none of this looks particularly legit from a meteorlogically realistic aspect, so the future like all of them....heads toward:

"Live as if you were living already for the second time, and as if you acted the first time as wrong as you're about to act now"

No comments:

Thursday, September 22, 2011

Only Thing to "Fall' on Friday Will Be Raindrops

The Sun’s away
And the bird estranged;
The wind has dropped,
And the sky’s deranged;.....

This morning 9/22/2011 at sunrise

......Summer has stopped.

And some are very frustrated about seeing it go so fast. My sentiments exactly.


Fall begins at 5:05 A.M. EDT, Friday morning. The autumnal equinox is defined as the point at which the Sun appears to cross the celestial equator from north to south. The word equinox means “equal night”: Night and day are about the same length of time. In addition to the near equal hours of daylight and darkness, the equinox is a time when the Sun’s apparent motion undergoes the most rapid change. Around the time of the equinox, variations in the position on the horizon where the Sun rises and sets can be noticed by alert observers from one day to the next. Eventually, it will be rising and setting along the southern horizons as we progress toward December 21-22 as the first day of the Winter Solstice approaches. 

TODAY: Deeper layer moisture is entering the picture as expected, although this still does not mean widespread rains due to lack of any boundaries and few triggers. Ample daytime heating though will give rise to  respectable upward motion (vertical velocities). The models are again a bit out of whack, with even the short term RUC rotating an  inverted mid-level trough from south to north during the day across South and Central Florida. This, in turn, would change steering currents from SSE to nearly SSW-SW by late today. Do not believe that will occur to such an extreme, but continued SSE-S Flow seems more likely, with winds closer to the ground remaining ESE-SE. This would progress the east coast sea breeze inland for the focusing mechanism for the peak storm period after 3-4pm west of I-95. If winds aloft do become more southerly, then outflow or even back building could work storms toward US1 north of Vero Beach by 5pm, to possibly the beaches from Daytona and north. Best hedged bet relies on storms remaining in the interior at this point though.

Up to this point this morning, it appears some showers with lightning from time to time generated from eddies off the western Bahamas,   worked into Palm Beach County. Since earlier this morning, they have been working up the east coast, with some renegade showers reaching the coast further north toward Flagler County. The showers seem to be increasing off shore now that the sun has risen. With that, perhaps the RUC has something there with the more SSE-S Flow to develop later in the day


But for now, it's probably best to rely on persistence, since there is nothing evident that would preclude a persistence forecast of past model trends. What is happening out in the Gulf is interesting though. It appears much of the activity there is being provoked by divergent Southern Branch jet stream winds...which will remain over the Gulf for at least 2 more days. These are shown further down in this post.

Showers along the East Coast should work north and possibly increase after 10AM. Some could contain lightning, more so after 11AM to noon. If so, outflow from these near the coast and just offshore combined with the prevalent ESE-SE flow at the surface will send boundaries inland for greater storm coverage. Storms could start to occur earlier today than in the past two days., possibly peaking between 3-5pm.
FRIDAY-SUNDAY: Not any change in line of thought for this time frame with an increased chance of thunderstorms   most anywhere. The pattern will eventually evolve as to end the morning rain showers near the coast or at least put a lid on the amount of them, with afternoon storms forming by early to mid-afternoon and ending near sunset. Storm motion will be slow, but they should work northward and  a bit toward the east, especially on Saturday and Sunday.

It was noted that a La Nina pattern was evolving or had evolved in August in a post over a week ago. What does that can mean as we work into winter? 

In regard to the tropics, tropical storms and hurricanes have hit Florida during La Nina events in October. So far, it looks unlikely to occur, at least through the first week of October. There has been, coincidentally since the La Nina Event was made public, a developing southern branch jet stream running across Southern California toward is quite apparent still in model guidance..and is expected to remain in place to varying degrees over the Gulf and near Florida for quite some time to come.

 Here is the forecast for today's jet stream and the forecast of October 6  
A general  discussion concerning La Nina years follows.  Note that from these images above and then  provided below, that a La Nina like  pattern seems to already be established. It does not mean this will always be the pattern all the time, just the more prevalent one. 

.La Niña conditions returned in August 2011 due to the strengthening of negative sea surface temperature (SST) anomalies across the eastern half of the equatorial Pacific Ocean (Fig. 1). With the exception of the far westernmost Niño-4 region, all of the latest weekly Niño index values were –0.5oC or less . Also supporting the return of La Niña conditions was the strengthening of the below-average subsurface oceanic heat content anomaly in response to increased upwelling and further shoaling of the thermocline across the eastern Pacific Ocean

The better model performance, combined with the historical tendency for significant La Niña episodes (as in 2010-11) to be followed by relatively weaker La Niña episodes, leads to increased confidence that La Niña will persist into the winter. While it is not yet clear what the ultimate strength of this La Niña will be, La Niña conditions have returned and are expected to gradually strengthen and continue into the Northern Hemisphere winter 2011-12.

The Climate Prediction Center defines. . ."La Niña conditions" as existing when: A one-month negative sea surface temperature anomaly of -0.5C or less is observed in the Niño-3.4 region of the equatorial Pacific Ocean (5ºN-5ºS, 120ºW-170ºW) and an expectation that the 3-month Oceanic Niño Index (ONI) threshold will be met AND An atmospheric response typically associated with La Niña is observed over the equatorial Pacific Ocean Across the contiguous United States, temperature and precipitation impacts
associated with La Niña are expected to remain weak during the remainder of the Northern Hemisphere summer and early fall, and to generally strengthen during the late fall and winter. 

During September-November 2011, there is evidence that La Niña favors an increased chance of above-average temperatures across the mid-section of the country, and an increased chance of above-average precipitation across the Pacific Northwest

La Niña episodes are associated with three prominent changes in the
wintertime atmospheric flow across the eastern North Pacific and North
America. The first is an amplification of the climatological mean wave
pattern and increased meridional flow across the continent and the eastern
North Pacific. The second is increased blocking activity over the high
latitudes of the eastern North Pacific. The third is a highly variable
strength of the jet stream over the eastern North Pacific, with the mean jet
position entering North America in the northwestern United States/
southwestern Canada.

Accompanying these conditions, large portions of central North America
experience increased storminess, increased precipitation, and an increased
frequency of significant cold-air outbreaks, while the southern states
experiences less storminess and precipitation. Also, there tends to be
considerable month-to-month variations in temperature, rainfall and
storminess across central North America during the winter and spring
seasons, in response to the more variable atmospheric circulation throughout
the period

No comments: