"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".

Tuesday, March 29, 2011

Chance of a Shower/Thunder Today - Strong or Severe Storms Wednesday/Thursday

Hail depth in the Orlando, Florida area on March 25, 1992! (image from an Orlando paper). It was written that this storm was considerably more costly to this area than Hurricane Donna of 1960 by many millions of dollars.
I've included the attached image as a gentle reminder that March Florida weather can be quite severe. In 1992 Central Florida experienced 2 significant hailstorms three weeks apart, the second and the most costly ones in Central Florida history.  More costly than Hurricane Donna's impact was to the Orlando area. Severe weather (but of what nature?) is becoming more likely for portions of the state beginning Wednesday afternoon/evening and again on Thursday.

RECAP: Boundary that was over North Florida yesterday, accompanied by moderate strength mid-level and upper level winds with weak energy aloft and a lot of moisture throughout the atmosphere yesterday provided the lift for continued rainfall across all of Central Florida.  The strongest weather related reports were those of winds in the 45-50mph over parts of Central and South Florida by the time all was said and done, but no severe category weather was reported.  Rainfall totals were 1-3" inches, with higher amounts determined per radar estimates. 

The strongest storms were associated with what is labelled as an MCS, a Mesoscale Convective System. This was pictured in yesterday's post per a satellite image.  By mid-late evening the boundary pushed toward South Florida as the upper level winds pulled off to the east, with the remnant energy that built up during the day over SW Florida/Keys (where it was rain free all day) generating some thunder in that area. Further north, the rains ended as the stronger winds pulled out, ending the lifting mechanism,  and as of this hour skies are anywhere from cloudy (South and north Florida) to nearly clear in some locations Central. Per surface observations and satellite imagery, it appears the boundary now lies across Broward County and westward north of the Keys. Fog is also being found in variety of locations, but all is quiet (the sun is shining at my location while typing).

TODAY: The atmospheric conditions today look a bit like a modified version of the standard summer day fare, so this unofficial blogcast will follow suit. Modified in the sense that it won't be as a warm as a summer day, but there is that ever looming possibility of a rain shower or thunderstorm.  

Winds today will be light, but mainly from the east this afternoon.  Although low level instability is weak this will be a bit overcome by remaining unusually cold air aloft. There remains plenty of low and mid-level moisture in place, as there really wasn't  a thorough "atmospheric colon cleansing" of the atmosphere behind the front.  Those reasons are about the only signal to support a rain / thunder chance today. What is missing for vigorous storms today is the lack of any moderate to strong upper levels winds/sea breeze/lake breeze convergences or mechanical forcing (although a 'see text' type storm is possible over South Florida (for SPC readers). There is not really any  upper level energy outlooked to pass over head (at least not of this writing), and the only location it appears there will be a sea-breeze collision will be over SW Florida, possibly as far north as Tampa Bay. Steering of showers/storms will remain generally from west to east by early afternoon but start to shift toward a more south to north direction by early evening as the boundary lifts north toward Central Florida , where supposedly it will be located by 8-10pm per 8pm (last night's) model guidance. Main threats from activity over South Florida are those inherent with any thunderstorm, namely lightning....although a strong downburst wind is also possible with the moist atmosphere and cold air aloft in place.

With this said, chance of showers and thunder mainly over SW Florida initially south of the boundary, but gradually spreading east and working north with time during the afternoon. Other showers/thunder could initiate further north near Tampa and work east with time.  It appears this activity will have a hard time reaching east of I-95 north of Martin County (near Ft. Pierce) due to the stabilizing marine influence of the easterly component wind up toward South Central to Central Florida, at least initially.  Best rain chance today looks to be on the west side of the state and all of South Florida/Keys. Secondary area (less likely is late) toward South Central and Central Florida proper, especially near the coast.

 Regarding Central. will be watching the motion of that boundary today to see just exactly how it behaves. What is happening is that it is waiting for the next approaching mid-upper level trough to approach from the west (which will impact much of Louisiana/East Texas for starters today).  As the troughs approach steering flow will be directed to more of a direction from the SE -S-SW with time overnight which will 'buckle' the boundary back north as an ill-defined pseudo-warm front. By tomorrow the same boundary will north of all of Florida.

Best chance of rain further north earlier today will be on the west side of the state west of Orlando (but moving east), then contingent upon the timing of the boundary's return northward, East Central Florida could get in on the much needed rain (although, not as needed prior to yesterday) by early -mid evening. Contingent upon how nice and sunny this afternoon remains over Central Florida, some of this activity (assuming it generates as anticipated) could easily contain thunder and some strong wind gusts. Local WRF model indicates a strong storm of 'see text' nature riding along the coast of Brevard early tonight, but I'm not buying it.

WEDNESDAY:  I've been expecting this day to be highlighted by 'official outlets' for a few days now, and finally (as of this morning) the Storm Prediction Center has upgraded their 'see text' for a portion of Florida to a "slight risk" of severe weather. Namely all of Florida along and north of the Beach Line (SR528)...a.k.a - "The Magic Dividing Line" so often referred to the past several months when it comes to delineating where various weather parameters begin to differ or converge over Florida. Must be the geography of the peninsula or something.  

In any case, the first of two (or more) more significant upper level disturbances to cross North Central/North Florida passes overhead. Actually, the signs of its forthcoming first begin to appear before midnight tonight in the form of stronger upper level winds spreading east from the Central Gulf, overspreading the north half of the state going into Wednesday morning. By morning  the warm front over South Florida this morning  will be well north of the state line. North/North Central Florida will be directly under the left exit region of a departing jet (upper level wind) max at 300mb as well as in a region of divergence aloft within the height region of the 250mb level jet (even higher in the atmosphere) by late afternoon as the troughs at various levels approach.  Very moist atmosphere otherwise and good start to daytime heating (although thermal instability will be somewhat limited), stronger instabilitiy in the mid-levels due to continued cold air aloft accompanied by these strong winds higher aloft will produce the lifting mechanism (per horizontally stretched helicity (coiled like winds) of modest value) to generate very strong to severe thunderstorms. Expect to see a tornado watch issued tomorrow if not already in place over the Panhandle at sunrise, with another watch to be issued further east and south...maybe as far south as the Beach line or Route 60/Sebastian Inlet. But at this point, no further south than a Cocoa Beach - South Tampa Bay line.

Further south, the wind fields decrease in strength significantly rather rapidly, however South Florida will have stronger instability. With that said, the most likely area to get a storm tomorrow further south of the more outstanding region noted above will be on the east side of the state as far south as Southern Palm Beach County later in the afternoon.

The events of Wednesday will NOT be in the form of a squall line, but rather rapidly moving discrete thunderstorm cells and small bowing line segments, particularly across far North Florida. Southern most extent storms will be more isolated...but any storm to erupt could contain hail and severe category winds. A tornado is possible, especially far North Florida/Panhandle, but not as likely working further south into North Central Florida (but you never know).  

Might end up seeing all the activity from near the Beachline passing just to the north over far north Brevard County (east coast residents)...hitting the Daytona area/Oak Hill/Mims.

WEDNESDAY NIGHT / THURSDAY: Looks as if activity will end rather quickly across Central/North Central Florida by early evening while the atmosphere 'locks and loads' for Thursday.  Much of what occurs across Florida on Thursday will be contingent upon how much remnant cloud cover or development of flat out clouds upfront limits instability from the get go.

However, wind fields that approach Central and North Florida on Thursday will be even stronger than those on Wednesday. Forecasts are showing jet stream level winds by late Thursday to be in the 100-120kt range, with even lower portions of the mid-levels in the 40+ kt range. These winds will be accompanied by very cold upper level temperatures once again by Florida Standards. The Storm Prediction Center (SPC) already has most of Florida in a 'Slight Risk" for severe weather on Thursday, but if skies clear up more than it is anticipated they will over night Wednesday night would not be surprised to see Central Florida upgraded to a 'moderate risk'. A rarity! Time will tell. 

Activity will be on the start at sunrise, over the Gulf, spreading east with time and reaching much if not all of Central Florida by late morning to near noon. Again, not anticipating a 'squall line', but rather a mish-mash on radar returns on TV of discrete storm cells and bowing line segments. Some quite vigorous, possibly intense. Radar could be quite the plethora of colors, like a painters pallet. Look out for the "dark red everlasting gobstoppers" and "purple meanies" and those 'spiraling thingy icons' the TV weatherman will point out. Those mean business.

The most likely area to receive this high chance of rain will be north of a Ft. Pierce  to just south of Sarasota line. Expect, if things develop as has been portrayed by the models now for over a week, that local TV channels will be broadcasting continuously "Live" in animated fashion by some point in time. That possibility also stands true to a lesser degree on Wednesday.

Guidance is not painting very  high precipitation totals over North Central Florida, although localized areas could receive over an 1'. This would be because, if my interpretation is correct, storms will more right along and not linger over any one area for long. Higher totals will be due to repeated passage of showers or storms in any one location. The highest totals are over far north Florida.

Further South toward South Florida, it gets sketchy. Models have been on again/off again with even a rain chance at all south of Palm Beach County on the east side. Curious. Believe strong subsidence aloft due to the 'so close yet so far' jet stream max is the reasoning models are tapering off the chance of even a rain drop to fall over South Florida, because that is where all the sun will shine early to heat things up.  Problem is, this area will likely be the most thermodynamically most a strong thunder storm  at a minimum cannot be totally ruled out, at least not at this point. SPC already has most of South Florida in a Slight Risk as well regardless of what the models are showing, namely because I'd think that it's simply too soon in time to determine (if ever possible) where to 'draw the line' of decreased active weather in this particular atmospheric set up.

FRIDAY/APRIL FOOLS: For two runs now, the models are showing a last and final surge of moisture and a weaker disturbance to cross far South Central and South Florida from early morning through noon time before the 500mb trough finally pushes further east. Thus, there may still be the chance of some rain/storms from Martin County and South through the Keys for the first half of Friday, while the north half of the state clears out.

WEEKEND: Pleasant with near normal temperatures, perhaps a bit below normal but still comfortable. No rain and light wind.

Next frontal boundary to approach on Monday. Chance of rain/storm increase on Tuesday. Do not expect that activity with the next system early next week (around April 5th) will be as strong (not nearly so), as the atmosphere will be barely recovered from the drying out we will experience over the weekend. The wind energy 'willing', but strong storms not "able". But that could change. Long time from now. All of the state could get rain as well early next week in a 'one shot deal'. Nothing lingering. 

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