Area Forecast Discussion
Issued by NWS
FXUS62 KTAE 251517
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
1017 AM EST Tue Nov 25 2014
.Near Term [Through Today]...
The 12 UTC surface analysis shows the surface cold front had
passed a TLH/VLD line but was stalling out across the Central Gulf
where surface cyclogenesis was beginning to take place. There`s a
tight dewpoint gradient analyzed, ranging from the upper 30s across
Southeastern Alabama into the mid 60s just ahead of the frontal
boundary. Initially, the low level drier airmass moving into
Southern Alabama will make measurable precipitation there
difficult, however the 06z data and the first bit of data from
the 12z model suite show moderate to strong isentropic ascent
developing from late this morning through the afternoon hours
initially across the Gulf and then spreading rapidly northward.
In fact, this already seems to be taking place across the Nrn
Gulf south of Pensacola and Mobile. As a result, expect this
forcing to help overcome the modest drier low level airmass, thus
most if not all areas of the forecast area will receive measurable
rainfall today, so have increased PoPs into the 90-100 percent
range across the board.
In terms of flood potential, though we`ve seen between 2 and 4
inches of rain (with isolated spots near 5 inches) across
portions of the region over the last three days, the rain has
occurred over a sufficient length of time that we should be able
to handle an additional 2 to 3 inches of rain in the next 24 hours
without any significant problems.
.Prev Discussion [355 AM EST]...
.Short Term [Tonight Through Thursday]...
Isentropic ascent of the 300K surface will be strongest during the
hours centered around 00Z Wednesday as the front remains stalled
over the area under parallel southwesterly flow aloft. DPVA will
also be in play. Therefore, we start out with categorical PoPs
across the board, as high as 100% across roughly the eastern half of
the forecast area. After that, forcing for ascent will drop off
precipitously after midnight with all PoPs ending before 18Z
Wednesday. For additional rainfall totals and any flooding concerns,
see the hydrology section below.
As cyclogenesis jumps to the coastal Carolinas, the colder air will
finally be drawn completely across the forecast area tonight. In
fact, temperatures will be chilly throughout this period. Look for
low temps by dawn Wednesday to range from the upper 30s over
Southeast AL and adjacent portions of the FL Panhandle to the upper
40s across the Southeast FL Big Bend. Highs both Wednesday and
Thursday will generally be closer to what we see in January with
lowers 60s common. A few spots across our northern zones will not
even quite make it to 60. Overnight lows Wednesday night will
generally be in the mid to upper 30s inland with 40s near the coast.
.Long Term [Thursday Night Through Tuesday]...
This period will be dry with surface high pressure in control.
Heights will also rise with zonal flow in place from the weekend
into Monday. However, the chilly air mass will remain in place
through Friday night with temps near or below even normal midwinter
levels. A few spots across the northern fringe of the forecast area
could touch freezing Thursday night and there could be some frost
Friday night. A moderating trend is expected from the weekend into
Monday. Some areas will see lower 70s degrees by Sunday with most
areas getting there on Monday.
[Through 06Z Wednesday] In general, there was a gradient in
observed conditions as of TAF issuance time from VFR to the
northwest, to IFR to the southeast, across the area. We expect
that trend to continue through the day, although it is likely
model guidance is being too optimistic with CIGS. A steady, cool
rain is forecast at most of the terminals, and that should help
lower cloud bases. In general, we are forecasting CIGS to trend
down into IFR or low-end MVFR at TLH and VLD, and trend down to
MVFR at ECP and ABY. DHN is most likely to stay at VFR for much of
the period. Visibility may be briefly reduced into the IFR range
at times in heavier rain or thunderstorms.
Small craft advisory conditions will first be achieved with offshore
winds speeds this morning. The nearshore legs will not see this
until later in the day. Winds will be strongest overnight and an
occasional gust to gale force will be possible. Conditions will drop
below advisory criteria, even offshore, Wednesday morning. After a
brief lull Wednesday afternoon, a return to cautionary conditions is
expected from Wednesday night into Friday. Winds will then drop
below headline criteria for Friday night and Saturday as they
finally veer to onshore.
Wetting rains are expected today with high RH. Drier air will arrive
on Wednesday and Thursday, but RH values are not currently forecast
to reach critical levels. Additionally, fuel moisture will be quite
high given recent rainfall.
Radar estimates that 2.5-3.5 inch rainfall totals have been common
since Saturday across most of our GA zones as well as northern and
western portions of the FL Big Bend and adjacent Panhandle. This is
causing rises on most area rivers. These slow rises will continue
for the next several days. Additional rainfall totals through
tonight will be around 2-2.5 inches for the southeastern 1/2 of
the forecast area. These rains are not expected to cause
significant areal or riverine flooding. However, the Ochlockonee
River could approach minor flood stage in 4-5 days.
.Preliminary Point Temps/PoPs...
Tallahassee 61 43 62 37 64 / 100 100 10 10 0
Panama City 57 44 63 45 63 / 100 90 10 10 0
Dothan 54 40 60 39 60 / 90 90 10 10 0
Albany 56 42 61 37 61 / 100 100 20 10 0
Valdosta 62 46 61 37 62 / 100 100 20 10 0
Cross City 68 49 64 37 65 / 100 100 20 10 0
Apalachicola 62 46 62 44 64 / 100 100 10 10 0
GM...Small Craft Advisory from 4 PM this afternoon to 7 AM EST
Wednesday 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.
Small Craft Advisory until 10 AM EST Wednesday for Waters from
Suwannee River to Apalachicola FL from 20 to 60 NM-Waters
from Apalachicola to Destin FL from 20 to 60 NM.