"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".

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.  

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