Area Forecast Discussion
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523 FXUS62 KTAE 210958 AFDTAE AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TALLAHASSEE FL 458 AM EST Sun Dec 21 2014 .Near Term [Through Today]...
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A stalled frontal zone across the Northern Gulf of Mexico will serve as the focus for the development of additional areas of rain across the area. Coverage and intensity of the rain will increase as a mid level impulse moves toward the Central Gulf States later this afternoon. While rainfall amounts will not be particularly heavy, coverage should be fairly high, especially across the eastern portion of the forecast area. With cloudy skies and cool northeasterly flow in place across much of the area on the north side of this boundary, have undercut guidance for max temperatures in Alabama and Georgia, where highs may not rise out of the mid 50s. .Short Term [Tonight Through Wednesday]... The +PV anomaly currently positioned along the Texas/Mexico border will elongate in the fast upper-level southwesterly flow and spread through the Southeast tonight through tomorrow. This will strengthen the high pressure wedge sprawling down the Appalachian mountain chain, and subsequently reinforce the cool airmass in place across the northern half of the Tri-State region. At the same time, low to mid level southwesterly flow will surge an unseasonably warm and moist airmass out of the southern Gulf into the northeast Gulf. Although the two features will not directly link up, a broad area of low pressure is expected to develop in the northeast Gulf overnight. What will start as light to moderate rain over the Big Bend and south-central Georgia (generated along sloping low-level isentropic surfaces in the 295-305K layer) will eventually become heavy rain as the low level convergence strengthens a warm front along the northeast Gulf coast between the aforementioned cool land based airmass and the warming Gulf airmass. The surface and mid-level features will likely link up best across the southeast Big Bend of Florida. In the unseasonably tropical airmass (1.5"-2"PWAT), 1 to 2 inches of rain may fall in this area tonight through Monday. Although there will likely be a brief respite late Monday afternoon through Monday evening, light to moderate rain will likely increase in coverage overnight as low-level isentropic ascent continues over the strengthening and nearing warm front. On Tuesday, a low-level jet will gradually strengthen under the stratiform rain shield. At the same time, a subtle southern stream anomaly will slide through the central Gulf and approach the northeast Gulf coast. In addition a very strong northern stream low pressure system will be digging into the Southern Plains. Diverging upper flow and the approaching southern stream wave will increase deep synoptic lift, while the subtropical wave will strengthening deep layer shear. These features will all combine some-time on Tuesday afternoon to support discrete thunderstorm development along the aforementioned warm front. Model consensus would suggest somewhere on the order of 50-60kts of deep layer shear, coupling with near 30kts of low- level shear to warrant a threat for supercell thunderstorms. The primary threat with these storms will be tornadoes and possibly damaging wind gusts. Tuesday night into early Wednesday morning a potent squall line associated with the northern stream trough will pass through the same favorable environment for severe thunderstorms. The primary threats along the squall will be QLCS tornado development as well as damaging straight line winds. The severe threat will probably continue into Wednesday morning/early afternoon across the southeast Big Bend as the cold front makes its way through the region. Between the storms on Tuesday and Wednesday, another 2-4 inches of rain will be possible. .Long Term [Wednesday Night Through Sunday]... In the wake of the aforementioned front, temperatures will fall to slightly below seasonal averages Wednesday night and Thursday, before warming to near normal to end the week. Next weekend will bring another frontal system, though this one appears much weaker with much less rain expected.
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&& .Aviation...
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[Through 06Z Monday] With a frontal zone in place just south of the Florida, an extensive period of IFR ceilings are expected across the area through at least 18z. These ceilings may lift to low MVFR in the afternoon in between periods of moderate rain. After 02z, ceilings should return to IFR regionwide through the end of the TAF cycle.
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&& .Marine...
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Cautionary level northeasterly winds will weaken through the day today and remain rather light through Monday. Then winds will turn southerly as a warm front moves into the northern Gulf. Expect advisory levels winds by Tuesday ahead of a cold front, persisting through Wednesday night in the wake of the front. Gust to gale force may be possible Tuesday night through Wednesday. Winds and seas will then subside once again to finish the week.
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&& .Fire Weather...
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Low level moisture will be abundant over the next few days with drier air moving in on Wednesday. Red flag conditions are not expected over the next week.
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&& .Hydrology...
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While there is still some uncertainty with respect to the exact placement of heaviest rainfall with the storm system on Tuesday and Wednesday, confidence is increasing in a period of significant rainfall occurring across the region. Storm total accumulations of 3 to 5 inches with isolated heavier amounts are possible with this system. Rainfall totals of this magnitude will increase the potential for localized flooding across the region, particularly during times of heaviest rainfall on Tuesday Night into Wednesday Morning. With area rivers and associated tributaries at or below normal flows for December, the currently predicted rainfall amounts are generally expected to produce only rises to action stage on most of the river forecast points. The notable exceptions to this may be within the Ochlockonee and Withlacoochee River Basins where there`s increased potential to reach minor flood stage later this week.
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&& .Preliminary Point Temps/PoPs...
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Tallahassee 60 56 67 62 67 / 70 80 50 70 100 Panama City 63 57 66 64 68 / 60 70 40 70 100 Dothan 56 51 61 57 66 / 50 50 40 60 100 Albany 55 49 59 56 66 / 60 70 50 60 100 Valdosta 57 53 65 61 69 / 70 100 70 60 90 Cross City 69 62 69 64 71 / 70 100 70 70 90 Apalachicola 63 61 68 65 69 / 70 80 50 70 100
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&& .TAE Watches/Warnings/Advisories... FL...None. GA...None. AL...None. GM...None. && $$ NEAR TERM...GODSEY SHORT TERM...HARRIGAN LONG TERM...HARRIGAN AVIATION...GODSEY MARINE...HARRIGAN FIRE WEATHER...GODSEY HYDROLOGY...GODSEY

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