Area Forecast Discussion
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827 FXUS62 KTAE 221347 AFDTAE AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TALLAHASSEE FL 947 AM EDT Tue Apr 22 2014 .Near Term [Through Today]...
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The local pattern this morning shows a mid/upper low amplitude shortwave trough at the surface...a low on NY/Que border with slow moving cold front across Nrn GA/AL. Satellite water vapor shows a large area of showers and Tstms along and ahead of front moving Ewd. In response..high pressure over the Ern Gulf shifts SWD allowing for increasing lower cloud cover from NW-SE approaching NW CWA as noted on Satellite VIZ. During the rest of today...shortwave trough axis move east of CWFA replaced by upstream ridging. This will push cold front to S/Cntrl AL/GA by sundown with chances of precipitation increasing into the late aftn. West winds ahead of front will increase to 10 to 15 mph. The deepest moisture and best lift with this system will stay to our north. Locally...poor mid level lapse rates and meager lower moisture translates to marginal instability and deep layer shear so chance for strong to severe storms not high. Still...H5 temps will be cool enough i.e. -14C combined with surface temps in the low 80s and dew points approaching 60 degrees...enough ingredients for at least isold Tstms. Since latest run has slowed down the front...onset of POPs have been modestly delayed. PoPs by late afternoon show sharp 50-10% NW-SE pop gradient. Kept mention of isolated to wdly sct TSTMS. QPF amounts will generally be under one-quarter of an inch. Max Temps will be in lower 80s inland areas and mid to upper 70s along the coast.
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&& .Aviation...
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[Through 12Z Wednesday]...As morning fog continues to clear out this morning, VFR cigs and vsbys will become prevailing. Around 18Z, thunderstorms will move in to the northern terminals (DHN, ABY) from west to east, exiting the area by around 00Z. Around 09Z, MVFR visbys and IFR-LIFR cigs possible again at most sites.
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&& .Prev Discussion [235 AM EDT]...
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.Short Term [Tonight Through Thursday]... The 500 mb positive tilted trough (currently beginning to cross the Southeast) will pass southeastward over our forecast area tonight, but the accompanying weak cold front will stall across extreme North FL and become oriented east to west. The forecast Q-vector and omega fields are not that impressive, which may help explain why neither the GFS or NAM MOS "likes" this system, and have PoPs of only around 20%. However, our local Ensemble of Convection Allowing Models (ECAM) forecasts good coverage of rain this evening across South GA & AL, and its PoP is in the 50-80% range (but only 20% around Tallahassee and Panama City). We blended the two sets of differing guidance to come up with a PoP of around 50%. All of the MOS and dynamical guidance forecast a strong weakening/drying trend after midnight. Despite lack-luster synoptic scale forcing and SBCAPE values of only around 1000 J/kg, a few thunderstorms are possible- perhaps aided by fairly steep mid tropospheric lapse rates of 6.5 deg/km. The lack of strong winds aloft, marginal CAPE, and the rapid onset of nocturnal cooling all make severe thunderstorms unlikely. Forecast updraft speeds are in the 10-15 m/s range, which are usually not enough to support severe hail. Despite the presence of a quasi-stationary front in extreme North FL on Wednesday, the PoP will be 10% or less as the mid troposphere warms and dries considerably. There may be a slight increase in deep layer moisture on Thursday afternoon, and with the frontal system still in the region, could lead to a shower or two. However, we`re only carrying a 10% PoP for now. Temperatures will be near climatology through the period, with lows in the 50s and highs in the lower to mid 80s. .Long Term [Thursday Night Through Monday]... The large scale Srn stream pattern commences fairly progressive with near zonal flow over Wrn states...weak trough over Cntrl states and weak ridging over Ern states. On Friday...ridging moves offshore leaving near zonal flow over SE region reflected in uni-directional flow on model soundings. Flow shifts to weak WNW flow into Sat. On Sun into Mon...upstream amplified ridging builds Ewd into Gulf region. At surface...ridge becomes established over Nrn Gulf thru Fri night. Then...a low well to the north of CWFA brings a trailing weak front to our area on Sat where it likely stalls by Sat eve providing a small chance of convection. Sheared out front then lifts back Nwd on Sun. This will place local area in warm sector allowing for a weak seabreeze to develop Sat-Mon. Next cold front moves into SE on Mon yielding a modest increase on precipitation across mainly NW half of CWA on Mon. With local area in warm sector...temperatures are expected to be slightly above climo with inland highs in the low to mid 80s and under the sea breeze influence...somewhat cooler at the coast. .Marine... Despite the front approaching from the north later today, then stalling across extreme North FL through Thursday, winds and seas on the whole will remain quite low. The exception will be a moderate increase in onshore winds and chop near the coast each afternoon because of the daily sea breeze. .Fire Weather... Red Flag conditions are not expected through the remainder of the week. .Hydrology... Most of our area rivers are above normal stage with many in flood stage. The Choctawhatchee at Bruce is forecast to reach major flood stage this morning, with several others in moderate flood stage. Most area rivers will crest soon or have already crested. The exception is the Suwannee River which will rise slowly for the remainder of the week. QPF amounts through tonight are expected to be a third of an inch or less (mainly in Southeast AL and Southwest GA), and should not have a major impact on river levels. The most up-to-date river forecast information can always be found on our AHPS page (below). http:/water.weather.gov/ahps2/index.php?wfo=tae.
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&& .Preliminary Point Temps/PoPs... Tallahassee 82 60 83 58 84 / 20 20 0 0 10 Panama City 78 63 79 63 78 / 20 20 0 0 10 Dothan 81 59 83 58 84 / 40 50 0 0 10 Albany 83 58 83 56 84 / 40 50 0 0 10 Valdosta 82 59 84 59 85 / 20 20 10 10 10 Cross City 80 59 83 59 84 / 10 10 10 10 10 Apalachicola 75 61 76 63 77 / 10 10 0 0 10 && .TAE Watches/Warnings/Advisories... FL...None. GA...None. AL...None. GM...None. && $$ NEAR TERM...BLOCK SHORT TERM...FOURNIER LONG TERM...BLOCK AVIATION...BLOCK/MOORE MARINE...FOURNIER FIRE WEATHER...BARRY HYDROLOGY...WESTON/FOURNIER

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