Area Forecast Discussion
Issued by NWS
FXUS62 KTAE 251532
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
1032 AM EST Wed Feb 25 2015
.Near Term [Through Today]...
Active weather is expected through tonight as a potent upper trough
swings through with a moderately strong area of low pressure
developing along the northern Gulf coast. Divergence aloft ahead of
the upper system coupled with strong lift ahead of the surface low
will lead to a large area of rain spreading over the forecast area
during the afternoon. With the stationary frontal boundary nearly
bisecting the forecast area, high temperatures will vary widely
today, with highs ranging from the upper 40s northwest to the lower
60s in the southeastern Big Bend.
As far as the threat of severe weather goes, there remains a non-
zero risk, particularly near the coast. Shear will be very strong
(even for our local cool season standards) thanks to very strong
wind fields just above the surface with 850 mb winds in the 60-70
knot range this evening. Expected 0-1 km shear values are up to 50
knots across the area with some of the convection allowing models
forecasting 50 knot environmental winds down as low as 1500 feet.
The track of the low pressure will be particularly important to
the severe risk as that will largely determine how much instability
makes it inland from the coast. Currently, we expect the best
chance of severe weather in a corridor stretching across Gulf,
Liberty, Franklin, and Wakulla counties starting late this
afternoon and lasting into the evening hours. It is in this area
where there is the best model agreement on a narrow wedge of
instability making it inland and overlapping with the very strong
shear values. Damaging winds and a tornado or two are the main
risks. Farther to the north, the degree of destabilization is
highly uncertain, although a marginal risk may exist into
southwest Georgia if the low tracks farther to the north.
Regardless, there is some elevated instability present according
to the BUFKIT forecast soundings, so isolated thunderstorms were
included up into Georgia.
.Prev Discussion [250 AM EST]...
.Short Term [Thursday through Friday]...
Although rain will mostly end by the beginning of the period
(12Z Thursday), clearing may not be absolute as model forecast
soundings are in good agreement in showing a moist layer trapped
just below the frontal inversion through much of Thursday. This
may lead to more cloud cover and a cooler day than models are
currently indicating. For now we trended things slightly in that
direction, although more significant changes may be needed if
models continue to show that boundary layer evolution.
More substantial clearing is expected Thursday Night and Friday,
although it should not continue to get colder. A 900-700mb
anticyclone will begin to re-establish off the Southeast Atlantic
coast, which should cause the air mass to begin to modify across
the region. Temperatures will still be slightly below normal.
.Long Term [Friday Night through Wednesday]...
Most of the extended will feature slowly rising heights and return
flow across the region. The increased moisture may bring some
periods of low cloud cover and a slight chance of some rain
showers, but the primary forcing mechanisms for rain chances will
remain off to the north and west. The main trend in this time
frame will be steadily rising temperatures. A few locations may
crack the 80 degree mark by early next week, although the current
forecast only reflects mid-upper 70s.
[Through 12z Thursday] Unsettled conditions will prevail through
the period as an area of low pressure moves along the Gulf
coast, bringing widespread rain to the area and the possibility of
thunderstorms and gusty winds to ECP and TLH by this afternoon
into this evening. Ceilings will lower into the MVFR to IFR range.
There was some consideration given to possibly issuing a Gale
Warning for most or all legs of the coastal waters. Model guidance
is consistently indicating a narrow band of gale force gusts just
in advance of the line of storms along the cold front. This is
likely due to a very strong jet of low-level winds just above the
surface. While we feel reasonably confident that gale force gusts
will occur, we currently think the spatial and temporal extent
will be limited to a scale of about 1-2hr or 30-50NM in advance of
the convective line. That is also supported by model guidance.
This falls somewhat short of the "frequent gust" requirement of
the GL.W criteria. Therefore, a strongly worded Small Craft
Advisory was issued instead with a supplementary bullet point in
the product regarding the gust potential. This will be monitored
today in case the area of gale force gusts becomes more expansive.
There are no fire weather concerns expected for the next several
days as afternoon relative humidities are expected to remain well
above critical levels after the wetting rains today and tonight.
Widespread rainfall totals of 1-2 inches are expected today
through tonight across the area with localized amounts in excess
of 3 inches possible. These totals will cause rises along our area
rivers and bring several sites along the Kinchafoonee Creek and
the Choctawhatchee, Ochlockonee, Aucilla, and Upper Withlacoochee
Rivers into action stage. The Withlacoochee River at Valdosta is
likely to crest near minor flood stage by the end of the week and
could reach a higher and earlier peak if rainfall totals end up
being higher than currently forecast.
.Preliminary Point Temps/PoPs...
Tallahassee 60 43 57 39 60 / 90 100 10 10 10
Panama City 59 44 54 40 57 / 100 90 10 10 10
Dothan 48 39 52 35 54 / 100 100 10 10 10
Albany 51 41 53 36 56 / 100 100 10 10 10
Valdosta 56 43 56 40 59 / 90 100 10 10 10
Cross City 66 53 61 43 63 / 40 90 40 10 10
Apalachicola 63 46 57 42 59 / 80 100 10 10 10
GM...Small Craft Advisory until 3 AM EST Thursday 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-Waters from Apalachicola
to Destin FL from 20 to 60 NM.