Area Forecast Discussion
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688 FXUS62 KTAE 210135 AFDTAE AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TALLAHASSEE FL 835 PM EST Thu Nov 20 2014 ...Heavy rainfall and strong storms possible late Saturday night into Sunday... .Near Term [Through Tonight]... High pressure centered across the Southern US will remain in place through the night allowing for one last night of good radiational cooling conditions. Satellite imagery does show the increase of mainly upper level cloudiness, and this may limit some of the cooling. Moreover, surface data from 21 UTC show that near surface moisture levels have increased markedly in the last 24 hours, with surface dewpoints back into even the lower 40s for portions of the Florida Panhandle. The driest airmass though still remains over the Florida Big Bend, thus with the very favorable radiational cooling conditions, will indicate one last night of freezing temperatures - though only 30 to 32 degrees in the Florida Big Bend. Elsewhere, we should manage to stay above freezing. .Short Term [Friday Through Saturday Night]... Friday will be a transitional day as high pressure moves eastward into the Atlantic and a developing storm system moves eastward across Texas toward the Western Gulf of Mexico. By Saturday this storm system will be approaching the Western Gulf with a large area of isentropic ascent ahead of it leading to the development of widespread cloud cover and rain across the Gulf. The best area of lift will shift quickly northward as the upper level system moves into the Mississippi River Valley on Saturday night. Expect rain to increase quickly across the region after sunset with moderate to heavy rain moving in late Saturday night. On the order of 1.5 to 3 inches of rain, particularly across western areas looks possible on Saturday night with lower amounts off to the east. The severe thunderstorm threat doesn`t appear as significant as it did yesterday. The Euro and GFS both show the warm front reaching the coast around 12z Sunday - slower than in earlier runs. Thus, the severe threat Saturday night may be confined to the coastal waters or perhaps right along the immediate coast. In the short term period, heavy rainfall is the primary threat. .Long Term [Sunday Through Thursday]... At the beginning of the long term period, extensive cloudiness with widespread rain will be ongoing across the forecast area. The best synoptic forcing for precipitation will be shifting north of the area after about 18z on Sunday. There is some concern that a squall line may move through the region once the warm front retreats far enough northward, though the 12z runs this afternoon have difficulty keeping enough forcing back in the warm sector to generate these storms. Thus, the severe threat and associated rainfall after 18z seem a little more questionable. And while there should be limited instability and plenty of shear at this time range, the necessary forcing may be lacking to support any organized convective activity. With the system being fairly progressive, expect conditions to improve steadily by Sunday night as the main upper level impulse moves into the Great Lakes. This will leave behind a weak boundary across the eastern half of the forecast area separating an increasingly dry airmass across the Mid South and a more tropical airmass across North Central Florida. As a secondary impulse rounds the base of a large scale eastern CONUS trough on Monday night into Tuesday, some of the guidance indicates the potential for scattered showers and storms. As a result, will maintain chance pops into Tuesday evening before finally clearing things out by Wednesday morning. Thereafter, most of the models are in good agreement that the Wed- Thurs timeframe will be dry as high pressure builds across the southeast. The only notable difference at this point is whether the airmass will be near normal or much cooler than normal as suggested by the 12z GFS. For now, have settled on a compromise solution between the two with slightly below normal temperatures across the region on Thanksgiving Day. && .Aviation...
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[Through 00Z Saturday] VFR conditions will prevail through the next 24 hours.
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&& .Marine... Light to moderate offshore flow will remain in place through this evening. Thereafter, the gradient will sharply tighten between a high pressure to the east and a strengthening low pressure system to the west. This will result in a prolonged period of advisory conditions starting on Friday night and continuing through Sunday. Strong to severe storms are possible across the marine area late Saturday night and continuing into Sunday. && .Fire Weather...Low level moisture will gradually increase beginning Friday with widespread rain overspreading the region Saturday through Sunday. && .Hydrology...A moderate to heavy rainfall event looks to be in the offering this weekend starting late Saturday night continuing into Sunday afternoon. Because the system will be progressive enough, widespread flooding is not anticipated at this time. However, synpotic forcing with this system is rather impressive, particularly from 03z Sunday through 15z Sunday, thus there is the potential in this timeframe for 2 to 4 inches of rain with isolated heavier totals, primarily across our western areas. Flows on area rivers are rather low and should be able to handle a couple of inches of rain without reaching flood stage - though widespread totals in excess of 3 or 4 inches may result in minor flooding at a couple of river points in the first half of next week, especially should this rainfall occur in the upper portions of the Choctawhatchee and Chipola River basins. In urbanized areas, minor flooding problems are possible, particularly on Sunday morning across the Florida Panhandle and into Southeast Alabama. Future forecasts may be able to better define impacts as our hi-res output starts to depict this system Friday afternoon. && .Preliminary Point Temps/PoPs... Tallahassee 33 68 46 70 64 / 0 0 10 10 90 Panama City 42 67 51 69 64 / 0 0 10 30 90 Dothan 38 67 44 66 59 / 0 0 0 10 90 Albany 35 67 43 66 59 / 0 0 0 10 90 Valdosta 34 66 46 69 61 / 0 0 10 10 90 Cross City 31 69 48 75 66 / 0 0 10 10 80 Apalachicola 40 66 52 68 66 / 0 0 10 30 90 && .TAE Watches/Warnings/Advisories...
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FL...None. GA...None. AL...None. GM...None.
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