AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
622 AM EST Thu Dec 13 2012
.UPDATE…Aviation section for the 12Z TAF issuance.
.NEAR TERM [Through Tonight]…
The shortwave and surface low pressure system will continue to exit
to our east while deep layer ridging builds into the local region in
its wake. The forecast challenges for today will be sky cover and
max temps. Surface high pressure will ridge NE to SW from New
England to east Texas with the wedge setting up for us locally.
Under these conditions wrap around moisture on northerly winds get
trapped under the frontal inversion and low level clouds are slow to
erode or move out of our region. Thus, will go with a pessimistic
sky cover today. The exception may be areas west of a Dothan to
Panama City line where skies are currently clear. Clouds probably
won`t begin to erode or move east until mid to late afternoon so
will lean close to the cooler MAV temps. For tonight, skies should
clear along with diminishing winds to allow temps to drop into the
mid to upper 30s most inland areas with lower 40s along the coast
and Dixie county.
.SHORT TERM [Friday Through Saturday]…
Deep layer ridging firmly in place Friday with seasonal afternoon
temps and dry conditions. Temps won`t be as cold Friday night as
winds swing around to the east and mid to upper level clouds spread
in from the west ahead of the next low pressure system. Saturday
will be a day of transition as the upper ridge flattens and the
surface ridge weakens allowing a cold front to edge closer to our
CWA. Clouds will further increase throughout the CWA but only a
slight chance for rain across SE Alabama in the afternoon.
Temperatures will elevate above seasonal levels as winds shifting to
the southeast and south.
.LONG TERM [Saturday Night through next Thursday]…
We continue to see model to model and run to run inconsistencies
with respect to the evolution of the upper level flow pattern and
associated frontal systems through the mid/long range periods.
Confidence in this part of the forecast remains below average. We
generally used a blend of HPC guidance and gridded MOS for most
fields. Details will need to be resolved later, but the general
trend shows a retreating ridge at the start of the period which
brings another day of warm temps on Sunday. A frontal system will
approach from the west. Chance PoPs (30-50%) were used with
highest northwest. As short wave energy moves from the Southern
Plains out into the Mid South, a wave develops on the front and
highest PoPs (40-60%) are realized on Monday as the front moves
through. We generally followed the GFS solution after that with
high pressure building eastward along the Gulf Coast in the wake
of the front. Since this air mass is of Pacific origin, temps will
generally be close to average behind the cold front. The next
frontal system is progged to approach on Thursday.
It should be noted that the 12/12Z Euro was much less progressive
and showed a deepening trough with a massive coastal low bombing
along the Southeast U.S. coast on Tuesday. The latest 00Z Euro is
closer to our preferred solution, at least in terms of sensible
[Through 12Z Friday]…
Little has changed in our thinking since the 06Z TAF issuance. DHN
and ECP are right on the edge of the low cloud deck and will be in
and out of it. We will begin the cycle with IFR ceilings at all
terminals. DHN and ECP will scatter out first during the morning,
followed by ABY in the afternoon. TLH and VLD will be last to
scatter and it could be as late as this evening. After that, VFR
is forecast for tonight.
Cautionary conditions over the coastal waters should drop below
these levels this afternoon as the pressure gradient weakens. Then,
we expect winds and seas to remain below headline criteria through
the weekend as winds gradually veer from northeast to southwest. A
cold front is forecast to pass through the local waters on Monday
with winds becoming offshore once again.
Relative humidity is expected to remain above critical levels
through much of the next week.