Area Forecast Discussion
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597 FXUS62 KTAE 250855 AFDTAE AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TALLAHASSEE FL 355 AM EST Tue Nov 25 2014 ...Another Day and Night of Rain on Tap for Most Areas Along with Cooler Temperatures... .Near Term [Through Today]...
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A band of moderate to heavy rain and embedded thunderstorms has developed across our forecast area early this morning, just along a surface cold front. The surface cold front will push southeast of our area today, but rain will be maintained along the sloped frontal surface to the northwest as a strong shortwave ejects east across Texas. The response to the ejecting wave will be a strengthening frontogenetic circulation - especially in the 18-00Z time frame. Model consensus places the strongest 925-700mb UVV roughly right where the rain band is already positioned as of 08Z - from Mexico Beach, to Quincy, to Tifton, and 25-30 miles either side of that. Rain should initially be quite focused in this narrow band, but will eventually expand in coverage as 00Z approaches with cyclogenesis commencing in the eastern Gulf of Mexico. During the daytime hours, though, we expect a sharp gradient in rain chances due to some dry low-level air working in behind the cold front. Model forecast cross sections cut through the front across our area from NW-SE show a wedge of drier air from roughly ECP-BIJ and to the northwest. This should limit northwestward progress of measurable rain today, although even our northwest zones should see some light rain by tonight. Given the strength of the frontogenetic circulation and precipitable water values about 1.5 to 2 standard deviations above normal, it is likely we will see some heavy rain at times today, particularly in the f-gen band. Heavy rain wording was added to the forecast with 12-hr QPF of 1.0-1.5" on average in those areas. To the southeast, scattered showers and thunderstorms should gradually increase in coverage through the day as low-level ascent becomes stronger with the developing surface low in the eastern Gulf. We went with a non-diurnal temperature trend for today. Cooler air will be working its way southeast across the area in the morning behind the surface cold front. However, abundant cloud cover and rain will likely maintain temperatures in the 50s for all but the eastern Florida Big Bend. By 18-20Z, the coolest temperatures in our area should be in the low 50s, roughly along the same rain band axis described earlier (Mexico Beach - Quincy - Tifton). Therefore, highs for a significant part of our area may occur early in the morning. The hourly temperatures were a blend of the RAP and 4km NSSL-WRF. .Short Term [Tonight Through Thursday]... Isentropic ascent of the 300K surface will be strongest during the hours centered around 00Z Wednesday as the front remains stalled over the area under parallel southwesterly flow aloft. DPVA will also be in play. Therefore, we start out with categorical PoPs across the board, as high as 100% across roughly the eastern half of the forecast area. After that, forcing for ascent will drop off precipitously after midnight with all PoPs ending before 18Z Wednesday. For additional rainfall totals and any flooding concerns, see the hydrology section below. As cyclogenesis jumps to the coastal Carolinas, the colder air will finally be drawn completely across the forecast area tonight. In fact, temperatures will be chilly throughout this period. Look for low temps by dawn Wednesday to range from the upper 30s over Southeast AL and adjacent portions of the FL Panhandle to the upper 40s across the Southeast FL Big Bend. Highs both Wednesday and Thursday will generally be closer to what we see in January with lowers 60s common. A few spots across our northern zones will not even quite make it to 60. Overnight lows Wednesday night will generally be in the mid to upper 30s inland with 40s near the coast. .Long Term [Thursday Night Through Tuesday]... This period will be dry with surface high pressure in control. Heights will also rise with zonal flow in place from the weekend into Monday. However, the chilly air mass will remain in place through Friday night with temps near or below even normal midwinter levels. A few spots across the northern fringe of the forecast area could touch freezing Thursday night and there could be some frost Friday night. A moderating trend is expected from the weekend into Monday. Some areas will see lower 70s degrees by Sunday with most areas getting there on Monday.
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&& .Aviation...
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[Through 06Z Wednesday] In general, there was a gradient in observed conditions as of TAF issuance time from VFR to the northwest, to IFR to the southeast, across the area. We expect that trend to continue through the day, although it is likely model guidance is being too optimistic with CIGS. A steady, cool rain is forecast at most of the terminals, and that should help lower cloud bases. In general, we are forecasting CIGS to trend down into IFR or low-end MVFR at TLH and VLD, and trend down to MVFR at ECP and ABY. DHN is most likely to stay at VFR for much of the period. Visibility may be briefly reduced into the IFR range at times in heavier rain or thunderstorms.
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&& .Marine...
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Small craft advisory conditions will first be achieved with offshore winds speeds this morning. The nearshore legs will not see this until later in the day. Winds will be strongest overnight and an occasional gust to gale force will be possible. Conditions will drop below advisory criteria, even offshore, Wednesday morning. After a brief lull Wednesday afternoon, a return to cautionary conditions is expected from Wednesday night into Friday. Winds will then drop below headline criteria for Friday night and Saturday as they finally veer to onshore.
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&& .Fire Weather...
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Wetting rains are expected today with high RH. Drier air will arrive on Wednesday and Thursday, but RH values are not currently forecast to reach critical levels. Additionally, fuel moisture will be quite high given recent rainfall.
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&& .Hydrology...
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Radar estimates that 2.5-3.5 inch rainfall totals have been common since Saturday across most of our GA zones as well as northern and western portions of the FL Big Bend and adjacent Panhandle. This is causing rises on most area rivers. These slow rises will continue for the next several days. Additional rainfall totals through tonight will be around 2-2.5 inches for the southeastern 1/2 of the forecast area. These rains are not expected to cause significant areal or riverine flooding. However, the Ochlockonee River could approach minor flood stage in 4-5 days.
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&& .Preliminary Point Temps/PoPs...
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Tallahassee 61 43 62 37 64 / 100 100 10 10 0 Panama City 57 44 63 45 63 / 100 90 10 10 0 Dothan 54 40 60 39 60 / 50 90 10 10 0 Albany 56 42 61 37 61 / 80 100 20 10 0 Valdosta 62 46 61 37 62 / 100 100 20 10 0 Cross City 68 49 64 37 65 / 90 100 20 10 0 Apalachicola 62 46 62 44 64 / 100 100 10 10 0
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&& .TAE Watches/Warnings/Advisories...
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FL...None. GA...None. AL...None. GM...Small Craft Advisory from 4 PM this afternoon to 7 AM EST Wednesday for Apalachee Bay-Coastal waters From Ochlockonee River to Apalachicola FL out to 20 NM-Coastal waters from Suwannee River to Keaton Beach FL out 20 NM-Coastal waters from Apalachicola to Destin FL out 20 NM. Small Craft Advisory until 10 AM EST Wednesday for Waters from Suwannee River to Apalachicola FL from 20 to 60 NM-Waters from Apalachicola to Destin FL from 20 to 60 NM.
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&& $$ NEAR TERM...LAMERS SHORT TERM...WOOL LONG TERM...WOOL AVIATION...LAMERS MARINE...WOOL FIRE WEATHER...LAMERS HYDROLOGY...WOOL

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