Area Forecast Discussion
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393 FXUS62 KTAE 171858 AFDTAE AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TALLAHASSEE FL 258 PM EDT Thu Apr 17 2014 ...Heavy Rain Likely Friday with Widespread Flooding Possible... .Near Term [Through Tonight]...
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The heavy rainfall event is still on track to begin late tonight as an area of low pressure develops in the Gulf along an enhanced low-level baroclinic zone. There is already evidence of this occurring as a large area of thunderstorms has developed today over the western Gulf as a potent southern stream disturbance ejects out of northern Mexico. A large area of stratiform rain is expected to overspread the western portions of the area tonight north of the surface low track, some of which could become heavy late tonight over the western areas. However, the vast majority of the heavy rain will hold off until during the day on Friday. PoPs will be low to start the night and then trend significantly higher as the night progresses. .Short Term [Friday Through Saturday Night]... The first half of this period will be marked by heavy rain and likely flooding. Aloft...Fri morning begins highly amplified with ridging over Wrn states and extreme Wrn Atlc. In between...exists an upper trough the result of srn/Nrn stream merging with a low over Wrn Gulf. During the day...a strong shortwave begins to cutoff from Nrn stream flow and develops a low that closes over Srn AL by sundown. This will induce significant divergent flow over Nrn Gulf of Mex. Low then advances Ewd to Ern seaboard Sat aftn and then offshore at night with upper ridging building into the forecast area overnight. At surface...In response to above upper trough/low...assocd low had already developed in Wrn Gulf with warm front ESE across Cntrl FL. By sunrise Fri...intensifying closed low lifts Newd to around 100 miles south of Pensacola with front lifting further Nwd. Under cutoff upper low...surface reflection slows down and with assocd large stratiform shield of moderate to heavy rain begins to strengthen and inch Newd. By sundown...upper low and surface reflection phase and become vertically stacked and along with lifting warm front quasi-stnry across FL Big Bend. Fortunately... another SRN stream anomaly will be propagating EWD into the Wrn Gulf overnight Friday, keeping a rather steady west wind aloft and allowing the surface low to gradually drift away from land into the Wrn Atlc by mid-morning Saturday. In its wake a ridge will build in. The forecast will focus on the combination of upper/lower features and their impact on heavy rain and flooding. Models have come into better agreement with the quicker GFS still a 6hr outlier. Area soundings during Fri shows totally saturated nearly uni-directional SSW profiles with PWATs around 1.8 inches. They are in agreement that widespread heavy rains will overspread our local area Fri into Fri eve, further aggravating ongoing river flooding with potentially significant impacts. At this time it appears as though 3 to 4 inches of rain will be common across SE AL, south Georgia, and north FL. With average amounts that high, confidence is increasing that isolated locations could pick up anywhere between 4-6 inches. That being said, this rainfall will likely fall over an extended period of time resulting in, for the most part, slow water rises. For that reason, a more general Flood Watch remains in effect as opposed to a Flash Flood Watch. However, the flash flooding potential is non-zero and will be highest near rivers currently running at high levels and in our more urban locations. With regard to strong to severe weather...guidance with better chance that with previous runs. On the one hand...extensive cloud shield should weak lapse rates aloft and we will have saturated soundings. However any diurnal heating should have modest impact on cape. Also approaching low should yield and increase in low and deep layer shear. so although overall risk not high...cant discount strong to an even isold severe storm if all ingredient come together. The focus will be across mainly the extreme SE Big Bend of Florida and adjacent waters in the afternoon. 100% chance of rain. Under cloudy and rainy skies...high temps will struggle to reach 60 across much of SE AL and Srn Ga with areas of SE Big Bend reaching to around 70. High Risk of Rip Currents from Walton to Franklin Counties in effect through Fri Eve. Possible coastal flooding issues will be addressed tonight. By Friday night, the heavy rain threat will have diminished, though wrap around light showers will continue on the back side of the departing low pressure until it has moved far enough east. Will go with 30-80% SW-NE POP gradient. A 20-40% chance of rain remains for Ern counties Sat morning but areas should be rain free by eve. Expect lows Fri night from near 50 Nrn tier GA counties to near 60 SE Big Bend..and in the mid 50s everywhere Sat night. Highs Sat will range from low-mid 70s in relatively cloud free west to mid 60s over cloudy NE Tier GA counties closest to departing low. .Long Term [Sunday Through Thursday]... By Sunday, upper and surface ridge build into the region. By Monday night...next weak trough and shortwave moves into Gulf region with weak zonal flow across local area. A surface low well to our NW brings a weak front to the Nrn Gulf before retreating back Nwd on Wed. This will bring a slight chance of rain and isold thunderstorms to the NRN counties Tues and Tues night followed by drying trend. Throughout the entire period, both high and low temps will shows a gradual warming trend. Inland highs Sun in the mid to upper 70s will rise to the mid 80s Wed and Thurs. Inland Lows Sun night in the low to mid 50s will rise by Thurs night to the low 60s.
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&& .Aviation...
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[Through 18Z Friday] Conditions will gradually deteriorate through the period as an area of low pressure develops in the Gulf. MVFR ceilings are expected to lower to IFR later tonight with rain spreading from south to north from late tonight through the day on Friday. Rain may be heavy at times during the day Friday.
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&& .Marine...
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Advisory level conditions will continue through this evening for the northern Gulf at the base of strong high pressure stretching down the eastern U.S. coastline. Late tonight a strong surface low will near our waters and may bring gale conditions through Friday for waters west of Apalachicola. Latest guidance shows increasing confidence in this so gale watch was upgraded to a warning for Wrn waters. To the east Advisory conditions will likely prevail through the passage of the low pressure. The possible gale conditions will subside by Friday night, with advisory conditions diminishing by Saturday evening.
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&& .Fire Weather...
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Low level moisture will quickly increase across the region with a wetting rain expected across the entire region from late tonight through Friday night. Drier and breezy conditions will then arrive for most of the weekend. However, it does not appear that RH will get low enough to be concerned about red flag criteria, especially with the wet fuels.
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&& .Hydrology...
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We continue to be on track for a moderate to heavy rainfall event across much of the forecast area Friday and into Friday Night. Rainfall totals of 2 to 3 inches are expected to be fairly common, with higher amounts perhaps up to 5 to 6 inches will be possible. In general, the rivers most likely to flood and have higher impacts will be in the Florida Panhandle and Big Bend where flows are already somewhat elevated. Where the heaviest rain falls, there should also be other flooding on smaller streams and creeks, as well as areas of high water in low-lying areas and fields. A more detailed hydrology discussion is available on our ESF (Hydrologic Outlook) product, which can be found here: http://www.srh.noaa.gov/product.php?site=NWS&product=ESF&issuedby=TAE The most up-to-date river forecast information can always be found on our AHPS page (below). http:/water.weather.gov/ahps2/index.php?wfo=tae.
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&& .Preliminary Point Temps/PoPs...
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Tallahassee 59 65 52 70 53 / 90 100 60 30 10 Panama City 60 65 55 73 57 / 100 100 40 10 10 Dothan 55 60 51 72 52 / 100 100 60 30 10 Albany 54 60 50 68 52 / 80 100 70 40 10 Valdosta 57 66 53 65 53 / 60 100 70 40 20 Cross City 62 73 59 69 53 / 60 100 60 30 20 Apalachicola 62 66 55 71 58 / 90 100 40 20 10
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&& .TAE Watches/Warnings/Advisories...
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FL...Flood Watch from 2 AM EDT /1 AM CDT/ Friday through late Friday night for Calhoun-Central Walton-Coastal Bay-Coastal Dixie- Coastal Franklin-Coastal Gulf-Coastal Jefferson-Coastal Taylor-Coastal Wakulla-Gadsden-Holmes-Inland Bay-Inland Dixie-Inland Franklin-Inland Gulf-Inland Jefferson-Inland Taylor-Inland Wakulla-Inland Walton-Jackson-Lafayette-Leon- Liberty-Madison-South Walton-Washington. High Rip Current Risk through Friday evening for Coastal Bay- Coastal Franklin-Coastal Gulf-South Walton. GA...Flood Watch from 2 AM EDT Friday through late Friday night 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...Flood Watch from 1 AM CDT Friday through late Friday night for Coffee-Dale-Geneva-Henry-Houston. GM...Small Craft Advisory until 2 AM EDT Friday for Apalachee Bay- Coastal waters from Suwannee River to Keaton Beach FL out 20 NM-Coastal waters from Apalachicola to Destin FL out 20 NM-Waters from Apalachicola to Destin FL from 20 to 60 NM. Small Craft Advisory until 8 PM EDT Friday for Coastal waters From Ochlockonee River to Apalachicola FL out to 20 NM- Waters from Suwannee River to Apalachicola FL from 20 to 60 NM. Gale Warning from 2 AM to 8 PM EDT Friday for Coastal waters from Apalachicola to Destin FL out 20 NM-Waters from Apalachicola to Destin FL from 20 to 60 NM.
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&& $$ NEAR TERM...DVD SHORT TERM...BLOCK LONG TERM...BLOCK AVIATION...DVD MARINE...BLOCK FIRE WEATHER...DVD HYDROLOGY...LAMERS

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