Area Forecast Discussion
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532 FXUS62 KTAE 270753 AFDTAE AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TALLAHASSEE FL 353 AM EDT Sat Sep 27 2014 ...HEAVY RAIN POSSIBLE SUNDAY INTO MONDAY... .Near Term [Through Today]...
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Today will be quite similar to yesterday, with essentially no deep layer synoptic forcing for ascent. Expect the day to start once again with low clouds just about everywhere across the Tri-State region. Scattering of clouds will be most likely later this afternoon, and west of a line from Albany through Apalachicola. Convection will develop offshore through the day today along a weak surface trough moving through the northern Gulf. With the Peninsula expected to be a few degrees warmer today, the thermally driven trough that develops over Florida will likely be a bit stronger than yesterday (especially further north through north- central Florida). This will result in more favorable convergence along the western part of the peninsula, and eventually into our southeastern Big Bend counties later today. Further supporting higher rain chances in the Suwannee Valley today will be the plume of anomalously high PWATs, taking us from slightly below normal moisture levels, to well above normal across north Florida and into our southern tier of Georgia and Alabama counties. High temperatures are forecast to reach the mid 80s region-wide today. .Short Term [Tonight Through Monday]... The main concern is the potential for heavy rainfall across the area and the potential for flash flooding. The GOES blended TPW shows a large area of precipitable water values over 2 inches across the Florida peninsula and stretching into the Gulf. This has also been sampled by the 00z Tampa sounding which had an impressive PWAT of 2.38 inches. As an upper trough approaches from the west on Sunday into Monday, this deep moisture will be pulled northward. In addition, a weak area of low pressure may develop along the Gulf coast on Sunday and lift northeastward on Monday, further enhancing low level convergence across our western counties, especially near the coast. Some of our local WRF runs are quite bullish on rainfall amounts along the panhandle coast. The very high totals seen on some of those runs may be a bit suspect due to overdeveloping the area of low pressure, but the large scale ingredients for some heavy rainfall look fairly favorable. In fact, the GFS ensemble mean precipitable water forecast for Sunday through Monday is up around the 99th percentile in terms of the model climatology (M-climate) for this time of year, which is impressive and by definition doesn`t happen very often. With this tropical airmass in place and some synoptic forcing in the area, heavy rain wording was used for the western half of the forecast area. A flash flood watch was considered, but with the main event not expected to be until Sunday into Sunday night, confidence was not quite high enough in the heaviest rainfall amounts to issue a watch this early. With the dry summer, flash flood guidance values are not particularly low either at the moment. Therefore, it seemed prudent to wait for the event to get a little closer and more into the range of the hi-res guidance ensemble to make a decision on any watches. .Long Term [Monday Night Through Saturday]... As the surface low and upper trough shift to our east Monday night into Tuesday we will see a gradual decrease in deep layer moisture along with significantly lower rain chances through the remainder of the week. Expect temperatures to run near or just above normal.
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&& .Aviation...
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[Through 06Z Sunday] IFR/MVFR ceilings will slowly lift, then scatter through the first part of the day. VFR ceilings are expected from mid-afternoon through the early evening when restrictive ceilings will likely overspread the region again. Scattered showers and thunderstorms may encroach on ECP, TLH, and VLD late in the day. The storms should dissipate over TLH and VLD within a couple hours, though should be expected at ECP through the night.
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&& .Marine...
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Northeasterly flow will shift to easterly today and become southerly by Monday ahead of a weak area of low pressure. Exercise caution conditions will likely continue across most of the area today. Somewhat elevated winds of 10 to 15 knots are expected for Sunday and Monday, but rather stormy conditions are also likely during that time with locally higher winds and seas near thunderstorms. A decrease in winds and seas is expected for next week.
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&& .Fire Weather...
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As we transition to a very wet pattern, there will be no fire weather concerns through at least early next week.
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&& .Hydrology...
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General rainfall amounts of 1 to 3 inches are likely across the forecast area through Monday, except 3 to 4 inches with locally higher amounts around 6 inches possible in a short period of time along the panhandle coast. These amounts are not expected to result in any river flooding due to low flows from the recent dry summer, although rises are certainly expected. However, isolated instances of flash flooding cannot yet be ruled out for Sunday into Monday, mainly along the panhandle coast and in the typically vulnerable urban and low-lying areas. If confidence continues to increase in this scenario, then a flash flood watch could be issued as early as this afternoon for Sunday.
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&& .Preliminary Point Temps/PoPs...
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Tallahassee 86 72 84 71 86 / 40 50 80 70 70 Panama City 84 73 81 74 85 / 30 70 90 70 70 Dothan 84 69 81 69 84 / 20 60 90 70 60 Albany 85 69 84 69 85 / 20 40 80 70 70 Valdosta 85 71 86 70 85 / 20 30 60 60 70 Cross City 86 71 86 70 86 / 70 40 60 60 70 Apalachicola 83 75 83 75 84 / 30 70 90 70 70
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&& .TAE Watches/Warnings/Advisories... FL...None. GA...None. AL...None. GM...None. && $$ NEAR TERM...HARRIGAN SHORT TERM...DVD LONG TERM...BARRY AVIATION...HARRIGAN MARINE...DVD FIRE WEATHER...HARRIGAN HYDROLOGY...DVD

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