Area Forecast Discussion
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742 FXUS62 KTAE 170830 AFDTAE AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TALLAHASSEE FL 430 AM EDT Thu Apr 17 2014 ...Heavy Rain Likely on Friday with Widespread Flooding Possible... .Near Term [Through Today]...
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Water vapor imagery and model analysis indicate a broad upper level trough over much of the CONUS this morning with a short wave moving from the Southern Rockies out into the Southern Plains. Surface analysis shows high pressure centered over New England ridging southwestward to the northern Gulf of Mexico with a front stalled over the southeastern Gulf and Yucatan Peninsula. Satellite imagery indicates low clouds encroaching on the forecast area from the east and south. This trend is forecast to continue through the day as isentropic ascent on the 295-300K surfaces steadily increases and pressure falls commence in the central Gulf as the upstream short wave approaches form the northwest. PoPs will be confined to our FL zones this afternoon and will mainly be in the slight chance category. Any precipitation that falls will be in the form of light stratiform rain. Despite the increase in cloud cover, temps will be a few degrees warmer than yesterday with highs ranging from the upper 60s north to mid 70s southeast. .Short Term [Tonight Through Saturday Night]... The entire short range forecast will revolve around a Gulf low forecast to bring heavy rain and flooding throughout the Tri-State region. The good news from a forecast standpoint is that models are coming into a better consensus regarding the track and intensity of the low; the bad news is that our confidence is increasing that widespread heavy rains will overspread our local area, further aggravating ongoing river flooding with potentially significant impacts. By tonight, an elongated southern stream +PV anomaly will have merged with a northern stream anomaly, consolidated and strengthened across the Southern Plains and Lower Mississippi Valley. As this feature moves over an enhanced low-level baroclinic zone across the northeast Gulf, surface cyclogenesis will begin. By early Friday morning, a closed circulation will have formed just south of New Orleans, with a large stratiform rain shield spreading across the northern Gulf. As the surface low intensifies under the large area of stratiform rain, so too will the upper level anomaly, though it will begin to cutoff from the northern stream flow as -PV advection occurs aloft atop the large rain shield. As the upper anomaly strengthens and cuts-off through the first part of the day Friday, the forward propagation of the surface low will slow, with the system becoming more vertically stacked by Friday night. Luckily, another southern stream anomaly will be propagating eastward into the western Gulf overnight Friday, keeping a rather steady west wind aloft and allowing the system across the Southeast to gradually drift away from land into the western Atlantic by mid-morning Saturday. A very moist maritime tropical airmass will be in place across the Tri-State region on Friday with PWAT values nearing 2 inches across north Florida. That is approaching +3 standard deviations above the norm. Further, synoptic ascent will be maximized locally with the proximity of the surface low and the deep layer ascent provided by the split flow regime. This will result in widespread heavy rainfall nearly all day on Friday. At this time it appears as though 3 inches of rain will be common across southeast Alabama, south Georgia, and north Florida. With average amounts that high, confidence is increasing that isolated locations could pick up anywhere between 3-6 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, have opted for a more general Flood Watch 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. Severe weather is not anticipated with this system, though a few thunderstorms may be possible across the extreme southeast Big Bend of Florida on Friday afternoon. One last thing to mention is that afternoon "highs" will be quite low across most areas on Friday with prolonged rain and cloudiness. Portions of south Georgia and southeast Alabama will struggle to reach 60 degrees while most other locations will top out in the middle 60s. By Friday night, the heavy rain threat will have diminished, though light showers will continue on the back side of the departing low pressure until it has moved far enough east. Most areas should be rain free by Saturday afternoon, possibly Saturday evening closer to the Suwannee River Valley. .Long Term [Sunday Through Thursday]... By Sunday, slight ridging will begin to settle in the area allowing for a break from precipitation. The next chance of rain occurs Tuesday when the flow will become more zonal and a shortwave to the north of our area will bring a slight chance of rain and isolated thunderstorms to the northern counties. Throughout the entire period, temperatures will be near climatology with highs in the lower 80s, and lows in the upper 50s.
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&& .Aviation...
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[Through 06Z Friday] MVFR ceilings will overspread the aerodrome from southeast to northwest during the 08-12z time frame and then remain in place for the remainder of the period. Exceptions include VFR ceilings AOB 4 kft at DHN and ABY during the afternoon and early evening hours and IFR possibly setting in toward the end of the period at ECP with the commencement of a steady rain.
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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. 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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Heavy rains across the FL Panhandle on Tuesday resulted in sharp rises on the Chipola River where the Altha gage crested about 2 ft above moderate flood stage. Only minor rises occurred on the Choctawhatchee, Apalachicola and Ochlockonee Rivers. Most of the area rivers have crested and are falling slowly, but steadily. More heavy rain is expected Friday. Rain totals of 1 to 3 inches are possible with 2 to 4 inches possible in the Florida Big Bend region. Isolated higher totals are possible. This will reverse the aforementioned recessions and likely return some rivers to flood that had dropped below in the interim. Also, stages continue to steadily rise on the Suwannee River and flooding is expected early next work week. As rain rates should be more gradual with this system than the last, and with the above rainfall totals expected to fall over 12-24 hours, the flooding threat with this next round of rain should be of the areal/river variety. The flash flooding threat should be lower. In other words, areas of existing high water or flooding may worsen... and areas of high water could also develop in places like fields or low-lying areas. River flooding will also be possible, particularly in rivers around the Florida Big Bend and Apalachee Bay region. 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 73 56 65 52 70 / 20 90 100 60 30 Panama City 72 57 65 55 73 / 20 90 100 40 10 Dothan 71 52 60 51 73 / 10 90 100 50 30 Albany 70 52 59 50 68 / 10 80 100 60 30 Valdosta 72 56 66 52 65 / 10 70 100 60 30 Cross City 75 62 73 59 69 / 20 70 90 50 20 Apalachicola 70 61 67 55 71 / 30 90 100 40 10
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&& .TAE Watches/Warnings/Advisories...
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FL...Flood Watch from late tonight 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. GA...Flood Watch from late tonight 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 late tonight 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 Watch from late tonight through Friday evening 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...WOOL SHORT TERM...HARRIGAN LONG TERM...LAMERS/HELLER AVIATION...WOOL MARINE...HARRIGAN FIRE WEATHER...WOOL HYDROLOGY...WOOL

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