Area Forecast Discussion
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743 FXUS62 KTAE 131430 AFDTAE AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TALLAHASSEE FL 1030 AM EDT Sat Sep 13 2014 .Near Term [Rest of Today]...
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The previous forecast remains largely on track, so only minor tweaks were made. The leading edge of an expansive stratus deck, roughly marking the location of a quasi-stationary front, extended from near Mobile to near Atlanta this morning. When combined with 14Z objective MSAS analysis of MSLP and observed winds, this places the front very close to the northwest corner of our forecast area. The environment along and immediately southeast of the front is characterized by mid-70s surface dewpoints and PWATs around 2" (per GOES sounder). Meanwhile, some drier air was encroaching on the southeast part of the forecast area based on the latest water vapor loops and objective RAP analysis. Tallahassee appeared to be on the cusp of the drier air, with a PWAT of 1.9" on the 12Z sounding. Therefore, the higher rain chances that were already included in the northwest half of the forecast area seem on track at this time. Convection-allowing models (CAM) almost unanimously show fairly widespread thunderstorm activity just ahead of the front in our SE Alabama and western Florida Panhandle zones after about 19-20Z. They also agree that the storms are likely to linger until a few hours after sunset again, particularly in the Florida Panhandle. PoPs were bumped up in the Florida Panhandle for the evening hours. With less convective coverage in the Florida Big Bend and south-central Georgia, those areas could see highs in the mid-90s again. To the north and west, highs should be from around 90 to the lower 90s. The 12Z Tallahassee sounding did indicate stronger E-NE flow than yesterday, likely due to the influence of the passing tropical wave to the south of the area. However, radar VWPs and RAP analysis place the axis of the deep mid-upper level ridge near the northwest corner of our forecast area with a notable weakness in the flow. This will likely lead to slow storm motions in the region with the highest PoPs. Slow storm motions, storm-scale interactions, and the moist environment will provide adequate ingredients for localized heavy rainfall. The heavy rain wording was maintained in the forecast. Some CAMs indicate rainfall rates as high as 4-5" in just under 2 hours, so isolated flash flooding will be possible. However, the threat is expected to be isolated enough to preclude the issuance of a Flash Flood Watch.
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&& .Prev Discussion [642 AM EDT]...
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.Short Term [Tonight Through Monday]... Although weak upper level ridging will continue to dominate the northern Gulf Coast and SE U.S during the remainder of the weekend and into early next week (before it is eventually replaced by a trof towards mid week), plenty of deep layer tropical moisture will continue to flow into the region from the Gulf of Mexico and western Atlantic. This will keep PoPs above climo through the short term period with daytime rain chances generally in the 40-50% range, with decent PoPs continuing well into the evening hours, especially tonight over NW portions of the CWA. Temps are expected to remain above normal as well, with highs mainly in the lower to a few mid 90s away from the coast, with overnight lows in the lower to middle 70s. .Long Term [Monday Night Through Friday]... The main uncertainty for the extended forecast is to what extent the weak system moving westward into the Gulf will impact our area. The collaborated NHC/WPC forecast takes the system westward to a position south of Houston by mid-week and keeps it weak. Deep moisture will continue to increase across the area with a stalled frontal boundary also in the vicinity. These ingredients point to an unsettled period coming up with an above average chance of rain by mid-week. Some locally heavy rain is possible given the weak boundary and deep tropical moisture expected to be in place. This could be further enhanced by the Gulf system depending on its evolution, but that evolution is much more uncertain. Daytime highs are expected to be held down in the mid 80s from Tuesday through most of the week given the expected cloud cover and increased rain coverage. .Aviation... [through 12z Sunday] Other than brief patchy fog early, generally VFR conditions are expected. Scattered to numerous SHRA/TSRA will develop this afternoon & evening across southeast AL, the FL Panhandle, & southwest GA, affecting KDHN, KABY, & KECP with occasional gusty winds, low cigs, and poor vis. Elsewhere VFR conditions will continue. SHRA/TSRA should slowly diminish around midnight or shortly after. .Marine... Winds and seas will be slightly elevated this weekend as a weak tropical disturbance passes well to the south of the coastal waters. Thereafter, a very weak surface pressure pattern will return to the marine area, with typically low summertime winds and seas expected once again. .Fire Weather... Red Flag conditions are not expected through at least this weekend. .Hydrology... As mentioned above, some locally heavy rainfall (with up to 2" to 4" amounts) will be possible today in some of the slow moving storms to the north and west of Tallahassee, but any heavy amounts should be isolated in nature and not have much of a hydrological impact through early next week. By the middle of the week, however, an upper level trof will replace the current ridge which will be retreating westward, and before the cooler and drier air is allowed to seep into the region by late in the week or next weekend, more widespread heavy rainfall could fall over the CWA. Should this occur, some more significant rises along area rivers and streams could take place, so this situation will be worth monitoring.
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&& .Preliminary Point Temps/PoPs...
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Tallahassee 96 73 93 72 92 / 20 30 40 20 50 Panama City 90 76 89 76 89 / 40 60 40 20 50 Dothan 91 72 92 72 92 / 70 60 50 30 50 Albany 92 72 92 73 92 / 50 50 50 30 50 Valdosta 95 71 94 71 93 / 20 30 40 30 50 Cross City 93 72 92 71 92 / 30 40 40 20 50 Apalachicola 90 77 89 76 88 / 20 20 40 20 40
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&& .TAE Watches/Warnings/Advisories... FL...None. GA...None. AL...None. GM...None. && $$ NEAR TERM...LAMERS SHORT TERM...GOULD LONG TERM...DVD AVIATION...FOURNIER MARINE...GOULD FIRE WEATHER...FOURNIER HYDROLOGY...GOULD

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