Area Forecast Discussion
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671 FXUS62 KTAE 230814 AFDTAE AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TALLAHASSEE FL 314 AM EST Fri Jan 23 2015 ...HEAVY RAIN AND A MARGINAL CHANCE FOR SEVERE WEATHER EXPECTED TODAY... .Near Term [Through Today]...
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The overnight analysis reveals that low pressure has developed as expected along the central Gulf coast. A well defined warm front is also located offshore of coastal Louisiana and Alabama stretching across our coastal waters north of the offshore buoys. The dewpoint gradient was quite impressive at 03z with New Orleans sitting in the mid 40s and the platforms just off the coast around 70. A large area of convection will affect the region today. In general, the convection allowing models (CAMs) have increased their QPF some compared to yesterday. This is due to a subtle difference in the orientation of the convection in the models that results in more training convection compared to previous runs. Looking at how tonight`s convection is oriented offshore on satellite imagery compared to the steering flow, these newer runs may have the right idea in signaling an increased potential for training convection today. The forecast soundings viewed in BUFKIT also show favorable heavy rain ingredients with MBE velocity vectors signaling a greater potential for training convection compared to yesterday. The large scale environment will also be very moist for this time of year with most models forecasting precipitable water values near or in the top 10 for the month of January (1.7-1.8"). Flash flood guidance values are around 4-5" in 6 hours across rural areas and around 3" or slightly less in some cases in the urban areas. These values are attainable in our area in training convection. The 1 hour flash flood guidance values for the cities are generally about 2", which could also be attainable if convection trains over a city. With these factors in mind, we have issued a flash flood watch for a swath of the area where we think the greatest threat of heavy rain exists today. In addition to the heavy rain threat, there is also a non-zero threat for severe storms today. As mentioned in previous discussions, this threat is conditional upon the location of the warm front. In general, have noted a slight northward trend in the models for the location of the warm front compared to yesterday. The SBCAPE values from the ensemble mean of the CAM guidance are in the 300-500 j/kg range across the Florida panhandle with around 100 j/kg in southwest Georgia. Although this does not seem like it a lot, it is enough given the expected high shear environment to support the potential for an isolated tornado or two as well as damaging wind gusts. Also noted the 00z NAM has mid 60s dewpoints reaching Albany now with SBCAPE values reaching 500 j/kg in southwest Georgia and over 700 j/kg in the panhandle. While this may be a little high given the expected widespread rainfall, the overall trend in the guidance is up, including the 00z GFS. .Short Term [Tonight Through Sunday]... By early this evening, surface low will be situated over SW Georgia, with the trailing cold front extending southward through Apalachicola into the Gulf of Mexico. Showers and isolated thunderstorms will remain widespread ahead of the front through the evening hours. However, the severe threat should diminish with the loss of daytime heating and veering of the low-level wind fields. The rain should be out of all but the eastern most counties by sunrise on Saturday with all areas being dry by mid- morning. A seasonably cool airmass will move into the region for Saturday, with highs holding in the mid to upper 50s. Sunday morning lows will drop into the mid 30s for most areas, before warming back into the lower 60s by afternoon. .Long Term [Sunday Night Through Friday]... Trough over the eastern states will be reinforced Sunday night as a strong shortwave drops towards the Mid-Atlantic states. This will push a dry front through the forecast area early Monday morning. The eastern trough is forecast to remain in place through most of next week with generally northwest flow aloft. This will keep the weather dry with temperatures near seasonal norms.
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&& .Aviation...
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[Through 12Z Saturday] Stormy conditions are expected today with moderate to heavy rainfall reducing visibilities along with convection. Gusty winds are also expected with IFR ceilings. Heavy rain and convection will diminish overnight, but ceilings are expected to remain in the IFR range.
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&& .Marine...
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Rough weather over the coastal waters is on tap for the next two days as a potent storm system moves through the southeastern states. Strong southerly flow is expected today ahead of the cold front with gale force gusts possible over the offshore legs, especially early in the day. Have trimmed back the Gale Warning a bit for today, with the strongest winds expected over the western offshore waters. Strong west to northwest flow will develop tonight behind the front, with more gale force gusts possible. Conditions will improve late Saturday into Sunday. However, strong winds will be possible once again by Monday.
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&& .Fire Weather...
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Heavy rainfall today will limit fire weather concerns.
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&& .Hydrology...
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The upcoming system for tonight and Friday is likely to produce a large area of 2-3" of rainfall with locally higher amounts. This will cause rivers across the area to rise, but most will likely remain below flood stage. Currently, the most vulnerable areas to minor flooding appear to be the Kinchafoonee near Dawson and the upper Withlacoochee near Valdosta. Ensemble forecasts show the potential for these sites to rise to minor flood stage. The highest rainfall is currently forecast along the Ochlockonee, so sites there may also be more vulnerable to minor flooding.
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&& .Preliminary Point Temps/PoPs...
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Tallahassee 68 50 58 35 62 / 100 80 10 0 0 Panama City 69 48 57 42 61 / 100 70 10 0 0 Dothan 64 43 54 36 60 / 100 80 10 0 0 Albany 64 46 56 35 60 / 100 90 20 0 0 Valdosta 68 52 58 36 61 / 100 90 30 0 0 Cross City 71 55 61 35 63 / 90 90 30 0 0 Apalachicola 69 51 58 41 60 / 100 80 10 0 0
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&& .TAE Watches/Warnings/Advisories...
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FL...Flash Flood Watch through this evening for Calhoun-Central Walton-Coastal Bay-Coastal Franklin-Coastal Gulf-Coastal Jefferson-Coastal Wakulla-Gadsden-Holmes-Inland Bay-Inland Franklin-Inland Gulf-Inland Jefferson-Inland Wakulla-Inland Walton-Jackson-Leon-Liberty-Madison-South Walton-Washington. GA...Flash Flood Watch through this evening for Baker-Berrien-Brooks- Colquitt-Cook-Decatur-Grady-Lanier-Lowndes-Miller-Mitchell- Seminole-Thomas-Tift-Worth. AL...None. GM...Small Craft Advisory until 7 PM EST Saturday 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. Small Craft Advisory from 7 PM this evening to 7 PM EST Saturday for Waters from Apalachicola to Destin FL from 20 to 60 NM. Gale Warning until 7 PM EST this evening for Waters from Apalachicola to Destin FL from 20 to 60 NM.
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&& $$ NEAR TERM...DVD SHORT TERM...CAMP LONG TERM...CAMP AVIATION...DVD MARINE...CAMP FIRE WEATHER...DVD HYDROLOGY...MOORE/CAMP

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