Area Forecast Discussion
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386 FXUS62 KTAE 301946 AFDTAE AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TALLAHASSEE FL 346 PM EDT Thu Oct 30 2014 .Near Term [Through Tonight]...
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The cold front has pushed through the area with cooler and drier air advecting in. The remaining cloud cover over the southeast half of the area will rapidly clear out. Overnight lows tonight will be cooler than recent nights with low to mid 40s across portions of southeast Alabama and mid 40s to near 50 elsewhere. .Short Term [Friday Through Saturday Night]... An initial cold front has ushered in a drier air mass already across the area; GOES blended precipitable water (PWAT) is estimating around 0.50" in Tallahassee. The dry air mass that will be in place on Friday should be sufficient to make the next cold front passage late Friday afternoon to Friday evening a dry one. This secondary cold front will be associated with a potent, digging +PV anomaly on the back side of a broad eastern US trough. As of 19Z today (Thursday), water vapor satellite indicated the +PV anomaly over southeast Manitoba. The GFS analysis indicated that the 1.5 PVU surface (dynamic tropopause) was down around 600mb, an indication that the digging wave is quite strong. By 12Z Saturday, the model consensus places a closed mid-level low over South Carolina with height anomalies around 5-6 standard deviations below normal. In meteorological parlance, this is quite unusual. With a deep and potent developing autumn cyclone for the Southeast region, one would expect strong cold air advection and windy conditions to the west of the low, behind the surface cold front. The standardized anomalies bear this out as well: over our forecast area models project the 850mb temperature anomalies peak at 4-5 standard deviations below normal, and the 850mb wind speeds peak nearly 3 standard deviations above normal. These signals suggest that the outer tails of the guidance distribution may actually be plausible scenarios in this case. With respect to temperatures, we expect this could produce high temperatures on Saturday that are very close to record cool values. The record for coolest high temperature on November 1st in Tallahassee is 57. The current forecast calls for 59 at TLH, with mid-upper 50s elsewhere, so it should be close. The model blend that we utilized for Friday Night and Saturday was weighted more toward raw model guidance (instead of MOS) as that tends to perform better in strong cold air advection regimes. For Saturday Night, winds should begin to decrease but the surface ridge axis will remain west of our forecast area with the high centered near the Ohio River. This should maintain some light winds and mixing through the night, so the low temperature forecast calls for values close to the consensus (mid 30s). If the winds can diminish sufficiently late Saturday Night, areas of frost would be more likely and a Frost Advisory may become necessary. Wind chills on Friday Night and Saturday Night should be in the low-mid 30s. Regarding winds on Saturday, we could approach Wind Advisory criteria. The anomalously strong winds near the top of the boundary layer should lead to higher wind gusts than we see behind most cool-season cold fronts. For now we have indicated wind gusts of 30-40 mph in the forecast, but some BUFKIT soundings (especially with the GFS) indicate the potential for gusts in excess of 40 mph depending on how deep the mixed layer is. .Long Term [Sunday Through Thursday]... The extended forecast will be marked by gradually moderating temperatures and mostly dry weather as a mid-upper level ridge builds across the eastern US and we transition into more of a +NAO/+AO regime. Highs should be closer to 80 degrees by the middle of next week. The next chance of rain is expected to hold off until Wednesday at the earliest.
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&& .Aviation...
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[Through 18z Friday] VFR conditions are expected to prevail through the period with light winds.
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&& .Marine...
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In the wake of the secondary cold front on Friday evening, we expect at least widespread advisory conditions with winds increasing to around 25 knots in most of the coastal waters. Given the strength of the wind field just above the surface and the warm early autumn water temperatures, frequent gale force gusts will be a distinct possibility. The much colder-than-normal air mass will combine with sea-surface temperatures that are above-normal to produce unusually steep lapse rates in the marine boundary layer. This should provide for efficient transfer of stronger winds to the water surface, and model consensus indicates these could be as high as 40-45 knots near the top of the boundary layer. Given the anomalous situation, we have issued a Gale Watch for all of the coastal waters from Friday Night into much of Saturday. Winds should subside later in the weekend, but periodic easterly winds at SCEC levels should persist into early next week.
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&& .Fire Weather...
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A much colder and drier air mass will push into the region over the weekend and bring high transport winds along with it. Red flag conditions are possible, particularly Saturday and Sunday, although the lower temperatures may keep our relative humidity values just shy of criteria.
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&& .Hydrology...
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Dry conditions are expected over the next several days, with no impacts expected along area rivers and streams.
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&& .Preliminary Point Temps/PoPs...
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Tallahassee 45 75 41 59 37 / 0 0 0 0 0 Panama City 52 72 45 59 42 / 0 0 0 0 0 Dothan 44 72 38 57 35 / 0 0 0 0 0 Albany 45 72 39 57 36 / 0 0 0 0 0 Valdosta 47 73 40 58 37 / 0 0 0 0 0 Cross City 50 75 45 59 37 / 10 0 0 0 0 Apalachicola 52 74 46 59 43 / 0 0 0 0 0
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&& .TAE Watches/Warnings/Advisories...
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FL...None. GA...None. AL...None. GM...Gale Watch from Friday evening through Saturday afternoon for Destin FL to Suwannee River out to 60 NM.
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&& $$ NEAR TERM...DVD SHORT TERM...LAMERS LONG TERM...LAMERS AVIATION...DVD MARINE...LAMERS FIRE WEATHER...MOORE HYDROLOGY...HARRIGAN

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