Area Forecast Discussion
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744 FXUS62 KTAE 141444 AFDTAE AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TALLAHASSEE FL 1044 AM EDT Mon Apr 14 2014 ...Strong to Severe Storms and Heavy Rainfall Possible from Late Tonight through Midday Tuesday... .Near Term [Through Today]...
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An overnight squall line over Mississippi and western Alabama is in the process of weakening as it encounters stable air over central and eastern Alabama. The weakening storms and trailing stratiform rain has set up a large arcing outflow boundary from NE LA - S MS - WC/N AL. There is also a well established cold pool and mesoscale high pressure behind this, centered roughly on Tuscaloosa at 14z. Nevertheless, there is still a thin band of convection on the downshear side of the cold pool that has been advancing steadily toward southeast Alabama. Extrapolation of recent trends would take it into our forecast area around 1630Z. Therefore, we maintained PoPs in the western part of our area during the daytime hours, although only "isolated thunderstorms" were mentioned due to the meager instability. Isolated showers continue to be advertised in the far eastern part of our area mainly between 16-21Z by a variety of convection-allowing models. It should be noted that existing CAM runs (and even global models) have not handled well the eastward progression of the convective line in Alabama. This may introduce a previously unforeseen mesoscale boundary into the area this evening that could provide an additional focusing mechanism for convective development. The next several hours should give us a better idea of whether or not this outflow boundary will play a role in shaping tonight`s weather. Looking ahead to tonight, recent model runs - particularly CAM - have increased QPF across our area. Therefore, look for an increase in the rainfall forecast later today. Depending on 12z guidance, a Flash Flood Watch may be considered for parts of the area as well, especially the Florida Panhandle west of the Apalachicola River. .Long Term [Wednesday Night 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 Southeast U.S.
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&& .Hydrology...
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Rainfall forecasts for tonight and early Tuesday are expected to be increased from previous expectations, especially in parts of the lower Choctawhatchee, Chipola, Apalachicola, and Ochlockonee River basins. In general, the additional rainfall tonight and Tuesday should slow the falling trend on area rivers and possibly lead to increases on some - particularly smaller basins. Therefore, we can say that at the very least flooding may be more protracted this week along some area rivers. However, given uncertainty on where localized heavy bands of rain set up, it`s difficult to say which rivers may see more 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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&& .Prev Discussion [337 AM EDT]...
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.Short Term [Tonight Through Wednesday]... The long wave trough over the center of North America will shift eastward during this period with a potent short wave rotating through its base as it crosses the forecast area on Tuesday. The associated cold front will sweep across the area from northwest to southeast from 09-21z Tuesday. Showers and thunderstorms will precede the front. At this time, it appears a squall line will enter the area around 02-04z and bring a threat for damaging wind gusts. The hail threat will be primarily north of the region, but our northwestern zones could get some hail. There is also a non-zero tornado threat of tornadoes, particularly in any discrete cells out ahead of the main line and closer to the greater instability near the Gulf Coast. By sunrise, the main band of convection is expected to be over the FL Big Bend and South Central GA. There still appears to be sufficient shear and instability in place at that time for a marginal severe threat in these areas before 18z. Most convection will exit east of the area by sunset. An unseasonably cold airmass will arrive behind the cold front with highs on Tuesday struggling to reach 60 degrees over Coffee County AL Tuesday afternoon. South Central GA and the FL Big Bend will peak in the lower 70s. Strong cold advection Tuesday night will drive temperatures down into the 30s for all but our southeastern FL Big Bend counties and coastal areas. This is about 15 degrees below normal. It does not appear that any records are in jeopardy, but wind chill reading will drop to around 30 degrees give or take a few. That winter coat may have to come out of the closet one more time. Highs on Wednesday will rebound to the upper 60s north to mid 70s southeast. .Aviation... [Through 06Z Tuesday] A patchy MVFR to IFR fog/ceiling mixture will be possible at ECP later this morning, though confidence is low due to the substantial coverage of high cloudiness. The only other restrictions through this afternoon could affect VLD late in the afternoon as showers and possibly isolated thunderstorms accompanied by low ceilings pass from south to north across the Suwannee Valley. Overnight a line of storms will move from west to east across the Tri-State region, likely bringing IFR (or lower) restrictions to terminals along and west of a line from ABY to TLH. .Marine... Onshore winds will pick up to cautionary levels tonight ahead of a cold front. After frontal passage, offshore winds will quickly increase to small craft advisory levels for Tuesday and Tuesday night before veering to the east and dropping to cautionary levels from Wednesday into Friday morning. .Fire Weather... Relative humidity levels will remain well above critical thresholds for the next couple of days as flow veers southerly ahead of an approaching frontal system that is expected to bring a decent amount of rainfall across the Tri-State region tonight through Tuesday. In it`s wake, the lowest relative humidities will be on Wednesday, but it is unclear whether durations or fuel moisture criteria will be met to warrant Red Flag conditions.
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&& .Preliminary Point Temps/PoPs...
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Tallahassee 83 64 72 37 72 / 10 70 80 10 0 Panama City 76 61 66 42 70 / 20 80 70 10 0 Dothan 82 57 63 36 69 / 30 90 60 10 0 Albany 82 62 68 36 70 / 10 80 80 10 0 Valdosta 86 63 74 38 73 / 20 60 80 20 0 Cross City 83 65 75 42 75 / 20 40 70 20 10 Apalachicola 77 64 69 42 69 / 10 70 80 10 0
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&& .TAE Watches/Warnings/Advisories...
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FL...High Rip Current Risk until 6 PM CDT this evening for Coastal Bay-South Walton. GA...None. AL...None. GM...None.
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&& $$ NEAR TERM...LAMERS SHORT TERM...WOOL LONG TERM...GOULD AVIATION...HARRIGAN MARINE...WOOL FIRE WEATHER...HARRIGAN HYDROLOGY...LAMERS

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