061 
fxus62 ktae 210732 
afdtae 


Area forecast discussion 
National Weather Service Tallahassee Florida 
332 am EDT sun Mar 21 2010 


Synopsis... 
the 03 UTC regional surface analysis showed a rather complex frontal 
system...with a cold front extending south from Arkansas into the 
Gulf...and a warm front near the la and MS coasts. An mesoscale convective system has 
developed in that area...and the Storm Prediction Center and our local WRF indicate 
there may be a sub-synoptic low pressure center (not yet evident in 
the pressure/wind analyses). The analysis may be complicated by the 
fact that the broader system is beginning the occlusion phase. Vapor 
imagery and upper data showed a strong closed low centered over the 
eastern Red River. This is a vigorous system...with strong winds 
evident from the surface up to at least the 500 mb level. The 
airmass behind this front was unusually cold for this time of 
year...with freezing/frozen precipitation reported in the Southern Plains 
and strong gusty winds. Rain was already spreading into South Alabama and 
the Florida Panhandle...though the very dry airmass ahead of this system 
will need to be moistened for a while before the rain can reach the 
ground father east. 


&& 


Short term... 
(today through tuesday) the rapid development and movement of the 
approaching frontal system is what will prevent a widespread severe 
weather outbreak here. The 00 UTC ktae sounding was very dry (a 
third of an inch of precipitation water)...and it is hard to believe that 
it will rain here just 12 hours later but all indications are that 
it will. However...the track of the approaching system (and 
accompanying rain shield) will not allow the warm sector to move 
inland. Even over the northern Gulf (where there was a little more 
sbcape) there have been few lightning strikes...despite the strong 
synoptic scale forcing. So...despite such a vigorous system with an 
unusually strong wind field...our severe weather threat is less than 
5 percent (within 25 miles of any point). But the threat is not 
quite zero because the winds aloft are so strong...and we can not 
completely rule out some storm scale processes producing a 
marginally severe wind gust at some point today. 


All the guidance forecast a dry slot to develop aloft over our area 
this afternoon...so we may even see partly cloudy skies later this 
afternoon (especially in the Florida panhandle). This will be short-lived 
as we expect clouds to fill back in tonight and even another chance 
for light rain. High temperatures will be a bit below average today 
(mainly because of the clouds and rain)...but temperatures will cool 
dramatically tonight in the wake of the cold front. Fortunately 
clouds and wind will prevent freezing temperatures. It will be cool 
during the day on Monday from the combination of cloud cover and 
cold air advection. We used a blend of the warmer MOS and cooler raw 
model output as a hedge. If there are more breaks in the clouds 
temperatures will make it into the middle 60s. If it is more on the 
cloudy side with patchy light rain/drizzle...temperatures will not 
get out of the 50s. Frequent wind gusts of 25 to 30 miles per hour will make it 
feel even cooler. Skies will clear Monday night...and as the winds 
go calm. Temperatures will be below average again (around 40 degrees 
inland). A slow warming trend will begin Tuesday afternoon...as deep 
layer ridging develops over the southeast. 


Long term... 
(tuesday night through sunday)...the early week upper low 
will be exiting the middle-Atlantic by Tuesday into Wednesday with 
upper ridging building into the southeastern states. This will allow 
temperatures to rise to near normal levels by mid-week. Another shortwave 
will approach the region by late in the week. Models differ on the 
strength of the system as it moves into region of confluent upper 
flow over the eastern Seaboard. European model (ecmwf) is stronger with the upper 
system and has a more defined band of showers and thunderstorms 
along the front late Thursday into Friday. The GFS is weaker with 
the upper system damping out as it approaches the East Coast. Gem 
currently supports the GFS solution. With the event still several 
days out...will bump probability of precipitation up slightly from previous forecast and add 
isolated thunder...a rough compromise between the two solutions. 


Air mass behind the late week system is not expected to be very 
cold...so seasonal temperatures will continue into the weekend. Another 
front may bring a chance of rain back in by next Sunday. 


&& 


Aviation... 
ceilings will continue to lower overnight and into the morning as a 
large area of rain overspreads the region. Ceilings will remain VFR 
for a few hours at the onset of precipitation but drop below bkn020 by 
12z at kdhn and kpfn...and by middle morning at the remaining 
terminals. The front will push through by early afternoon with 
winds shifting to the southwest and increasing to around 15 knots 
with gusts above 20 knots. May see ceilings lift to VFR briefly in the 
afternoon before wraparound moisture moves in and drops them back 
to MVFR. 


&& 


Marine... 
winds and seas had not yet reached advisory levels as of 
06 UTC...but they soon will...and advisory conditions will likely 
persist into Tuesday (mainly because of the high seas). We blended 
all of the numerical guidance for the wind forecast to smooth out 
each run's noisy patterns and to knock down the GFS wind speeds a 
bit. The resulting winds are still expected to cause a high 
surf/high rip current event for our Florida Panhandle coast today and 
Monday...and possibly even into Tuesday. Above-normal tide levels 
are expected across portions of the Florida Panhandle and Apalachee Bay 
coasts today...with tide levels up to a foot above normal. This is 
typically not high enough to cause significant problems. 


&& 


Fire weather... 
low level moisture will increase quickly today ahead of the 
approaching cold front. Drier air will filter in behind the front 
for Monday. However...lower temperatures will keep relative humidity values above 
critical levels. Next chance for red flag conditions not until the 
middle of the week as temperatures warm into the middle and upper 
70s. 


&& 


Preliminary point temps/pops... 
Tallahassee 65 44 63 40 69 / 90 30 20 0 0 
Panama City 61 47 59 45 65 / 80 30 20 0 0 
Dothan 65 39 60 40 69 / 80 20 20 0 0 
Albany 66 41 60 39 69 / 90 30 30 10 0 
Valdosta 65 44 62 41 68 / 90 20 30 10 0 
Cross City 69 47 65 41 68 / 90 20 30 10 0 
Apalachicola 63 49 61 45 64 / 90 40 30 0 0 


&& 


Tae watches/warnings/advisories... 
Alabama...none. 
Georgia...none. 
Florida...high surf advisory from noon today to 7 am CDT Tuesday for the 
following zones: Bay...coastal Walton...Gulf. 


GM...Small Craft Advisory until 2 PM EDT Tuesday for the following 
zones: Apalachee Bay or coastal waters from Keaton Beach to 
Ochlockonee River Florida out to 20 nm...coastal waters from 
Ochlockonee River to Apalachicola Florida out to 20 nm...coastal 
waters from Suwannee River to Keaton Beach out 20 nm... 
coastal waters from Apalachicola to Destin Florida out 20 nm... 
waters from Suwannee River to Apalachicola Florida from 20 to 60 
nm...waters from Apalachicola to Destin Florida from 20 to 60 
nm. 


&& 


$$ 


Long term/aviation/fire weather...Camp 
rest of discussion...Fournier 

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