Area Forecast Discussion
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248 FXUS62 KTAE 142111 AFDTAE AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TALLAHASSEE FL 511 PM EDT Mon Apr 14 2014 .Near Term [Through Tonight]...
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Subjective analysis at 18Z placed an outflow boundary from Gulfport MS, to Mobile AL, to Troy AL, to Columbus GA - or very near the northwest corner of our forecast area (Coffee Co AL). The cold pool behind the outflow boundary was characterized by temperatures in the 60s with cloudy skies and light to moderate rain. Meanwhile, a subtle coastal front extended from near Dauphin Island, Alabama to Apalachicola. These two boundaries could play a role in focusing convection later tonight. Models are in good agreement in showing fairly widespread thunderstorm development in the next 6 hours (by 03Z) ahead of a strong, advancing cold front to our west. This activity then would move across the area from west to east, mainly between 06Z and 16Z. The environment should support heavy rainfall in thunderstorms, with PWATs expected to be around 1.8-1.9 inches (approximately 2-3 standard deviations above normal, or in the 99th percentile for TLH April climatology). PoPs were increased to 90-100% and heavy rainfall wording was inserted. Convection-allowing models (CAM) are consistently showing a band of heavy rainfall along the Gulf coast tonight and Tuesday morning from southeast Louisiana into our local area (especially the Florida Panhandle). Although they vary slightly in the placement of this relatively narrow band, the rainfall totals are fairly consistent: an inch or so outside of the heavier band, 2-4" within the band and isolated totals possibly double that in very localized areas. Additionally, an ingredients-based assessment supports some brief (2-3hr time scales) training of convective elements. The SEwd drifting outflow boundary may combine with the Nwd lifting coastal front to create a WSW-ENE oriented thetaE gradient that could aid in focusing thunderstorms. A strengthening southwesterly LLJ should increase low-level moisture flux and forcing along the boundary as well as in the broader WAA regime. These factors, combined with the high precipitable water values, all suggest a heavy rainfall and possibly flash flooding threat. For that reason, we have issued a Flash Flood Watch for most of the area except the Apalachee Bay and eastern Florida Big Bend counties where models are consistently showing less QPF. Regarding the severe weather threat, isolated severe storms can`t be ruled out. The main threat would be damaging winds. We expect the highest chances of severe storms would be along and south of I-10 where greater instability should exist along and south of the coastal front.
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&& .Short Term [Tuesday Through Wednesday night]...
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The main band of convection (with some strong to severe storms and locally heavy rainfall) with the approaching cold front will be ongoing across much of the CWA on Tuesday morning, before a stronger Sfc low develops and ejects to our NE and begins to rapidly sweep the cold front through the CWA during the afternoon. Given the expected fast movement of the pre-frontal squall line, the overall threat for flash flooding will be decreasing from west to east across the CWA, with the SE FL Big Bend anticipated to receive storm total rainfall on the order of 1 to 1.5" when all is said and done. While this is not expected to cause any areal or flash flooding in this region, riverine flooding along the Aucilla and Suwannee Rivers will remain a distinct possibility. After the cold front moves through, much colder and drier air will rush in from the northwest on Tuesday night. Despite plenty of numerical guidance which is indicating low temps possibly reaching the freezing mark or below across portions of the western interior, believe this is a very unlikely scenario given the saturated ground and elevated winds overnight. Nevertheless, even the raw model data is quite cold for this time of year, so used a blend of the raw GFS and SREF, which still results in enough cold air advection to produce a fairly large area of low temps in the mid to upper 30s, which is about 15 to 20 degrees below climatology! A sunny but cool and dry day is expected for Wednesday, with highs only reaching the mid to upper 60s in most areas, with a few lower 70s well to the SE. Wednesday night will still feature below normal temps with lows in the lower to mid 40s to the north and upper 40s to around 50 to the south. .Long Term [Thursday Through Monday]... With the first low pressure system long gone by the beginning of the extended period, we should at least experience a 2 day break in the unsettled weather on Wed. and Thu. with an initial shot of unseasonably cold air moderating back towards climo levels. By the end of the week and through next weekend, however, the fcst will once again become quite difficult as the conditions are leaning heavily towards yet another very unsettled period. While the details on timing, potential rainfall totals, and the possibility of any severe weather have been very inconsistent from run to run in both the GFS and ECMWF, the chances of another significant rainfall event during this time frame are clearly increasing. This is definitely not welcomed news for our area rivers and streams, many of which remain elevated from previous rainfall events, and will be primed yet again by the initial rainfall event early in this week. Furthermore, until a more significant change in the synoptic pattern becomes evident across the CONUS, these anomalous digging shortwaves and potential heavy rainfall producers will continue to threaten the SE U.S.
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&& .Aviation...
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[through 18z Tuesday] Generally VFR conditions this afternoon should gradually give way to IFR CIGS overnight, with stratus likely spreading inland from the coast. Therefore, ECP and TLH should be affected first, followed by the inland terminals. Thunderstorms will advance across the area from west to east, and should affect all of the terminals at some point between 05Z in the west and 17Z in the east. Some of the storms could produce gusty winds and heavy rainfall with brief VIS reductions to LIFR.
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&& .Marine...
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Onshore winds and seas will gradually increase to cautionary levels tonight as series of developing waves of low pressure to our west will move northeastward from central LA to a position well to the north of the marine area by Tuesday morning. The final and strongest surface low in this series will then push a strong cold front from west to east across the waters on Tuesday, resulting in quickly developing Small Craft Advisory conditions as winds shift from southwest to northwest. Then, strong northerly winds will linger through Wednesday morning before the Advisory level conditions slacken as the winds become northeasterly in the afternoon. However, this break in the adverse marine conditions is expected to be short lived, as moderate to strong easterly winds are expected to quickly return and then last throughout the remainder of the week.
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&& .Fire Weather...
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Widespread wetting rain is expected later tonight and into Tuesday morning. This should limit fire weather concerns over the next 24 hours and increase fuel moisture. A drier air mass is expected on Wednesday, but fuel moisture levels should continue to be high.
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&& .Hydrology...
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Rainfall forecasts for tonight and early Tuesday continue to point toward increased confidence in a localized convective band of heavy rain setting up from the FL panhandle up toward southwest GA. In the area where any band sets up, rainfall amounts could easily range from 2 to 4 inches with higher amounts likely. Convectively induced heavy rainfall in any given area could result in flash flooding, especially over urban locations, with the general area of concern north and west of a line from Apalachicola to Tallahassee to Valdosta. River basins more likely to be affected include parts of the lower Choctawhatchee, Chipola, Apalachicola, and Ochlockonee. Additional rainfall tonight and Tuesday will slow the falling trend on area rivers and lead to rises on some, particularly in smaller basins. This will result in longer lived flooding this week along some area rivers, but given the uncertainty on where localized heavy bands of rain set up, it`s difficult to say which rivers may see the most notable rises. For real-time detailed river stage monitoring refer to this page: http:/water.weather.gov/ahps2/index.php?wfo=tae
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&& .Preliminary Point Temps/PoPs...
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Tallahassee 65 71 39 70 47 / 90 90 10 0 10 Panama City 64 68 43 67 52 / 100 70 0 0 10 Dothan 59 64 36 66 43 / 100 80 0 0 10 Albany 64 65 36 66 43 / 100 90 0 0 10 Valdosta 65 68 40 69 45 / 40 90 10 0 10 Cross City 66 73 43 72 48 / 10 90 10 0 10 Apalachicola 66 69 45 66 55 / 60 80 10 0 10
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&& .TAE Watches/Warnings/Advisories...
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FL...Flash Flood Watch from 10 PM EDT /9 PM CDT/ this evening through Tuesday morning for Calhoun-Central Walton-Coastal Bay- Coastal Gulf-Gadsden-Holmes-Inland Bay-Inland Gulf-Inland Walton-Jackson-Leon-Liberty-South Walton-Washington. High Rip Current Risk until 6 PM CDT this evening for Coastal Bay-South Walton. GA...Flash Flood Watch from 10 PM EDT this evening through Tuesday morning for Baker-Ben Hill-Berrien-Brooks-Calhoun-Clay- Colquitt-Cook-Decatur-Dougherty-Early-Grady-Irwin-Lanier- Lee-Lowndes-Miller-Mitchell-Quitman-Randolph-Seminole- Terrell-Thomas-Tift-Turner-Worth. AL...Flash Flood Watch from 9 PM CDT this evening through Tuesday morning for Coffee-Dale-Geneva-Henry-Houston. GM...Small Craft Advisory from 8 AM Tuesday to 2 PM EDT 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-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...GOULD LONG TERM...GOULD AVIATION...LAMERS MARINE...GOULD FIRE WEATHER...LAMERS HYDROLOGY...LAMERS/HOLLINGSWORTH

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