AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
900 PM EST Wed Feb 22 2012
SYNOPSIS...
AT UPPER LEVELS...
The large scale longwave pattern is highlighted by a LOW-AMPLITUDE
TROUGH/CUTOFF low over Baja CA and and the northeast portionĀ  of the
country, with a similarly low-amplitude RIDGE over PAC NW and
Rockies. This Baja low is expected to MEANDER slowly EWD over
northern Mexico through Friday. Another SHORTWAVE over PAC nw will
amplify AS it continues to dig east-southeast, reaching the Ohio
River Valley by early Friday.

AT LOWER LEVELS...
A broad diffuse HIGH PRESSURE ridge extended north of the Bahamas
through the southern Florida peninsula. Generally lower pressure was
found to the northwest OF CWA. In between, warm FRONT near the
coast. This combination has SET up broad southerly low-level FLOW
over much of the Southeast.

On Thurs, an H5 Trough lingers over N FL with WSW flow and 40kt JET
over area. warm front should lift new during days enhanced by jet.
This should lead to BREEZY to WINDY conditions approaching WIND
ADVISORY criteria, particularly over the northern third of our
forecast area.

As the above upper level shortwave digs and amplifies, surface
CYCLOGENESIS should commence from the Dakotas tonight into the
eastern Great Lakes by Friday. An accompanying cold front trailing
to the southwest will also SURGE southeastward across much of the
central and eastern US, reaching the eastern Gulf Coast on Friday
and will LIKELY be our next STORM system. Until that cold front
passage occurs, there will be periodic chances of RAIN and storms
with breezy south to southwest winds.

There is better model consensus today on the timing of the cold
front, reaching roughly the I-65 corridor just northwest of our area
shortly after SUNRISE, and pushing into the southeast part of our
area (near Dixie County) by 00z Saturday. This places the arrival of
the front squarely in the DIURNAL timeframe, and that`s when the
highest (approx 60%) POPS were concentrated. as the upper level
trough and cold front move SEWD and phase with lingering H5 Trough
over local area. The main concern then is related to potential
severe weather which remains a possibility and will dealt with in
more details on next AFD.

&&

.SHORT TERM [REST OF TONIGHT THRU EARLY THURSDAY]...
Analysis during wed AFTN/early EVE was due to upper shortwave
moving ewd across NB most Apalachee Bay. At surface weak warm front
from SRN la ESE thru the warm gulf CURRENT to our west and then
across and shelf waters of Gulf of MEX. This combination provided
enough lift for ample rain and SCT thunderstorms especially over SE
Big Bend and Apalachee Bay. However, activity waned last FEW hours
as initial shortwave moved ewd reaching E coast by 9PM with some
drying in its WAKE. Also, earlier large scale warm and MOISTURE
ADVECTION shifted NWD. However, AT 9PM another albeit weaker
shortwave was moving ENE across Apalachicola Bay generated showers
across se Big Bend and adjacent waters. Have updated ZFP to lower
pops thru 06z with MAX 60% over water down to less than 20 PCT NRN
tier counties. (ALTHO some light DRIZZLE a good bet over CWA).
satellite PIX implies a few more impulses may move in from waters
later tonight so cant drop pops too much. For 06z-12z, 0-40% NW-SE
GRADIENT with ISOLD tstms across mainly coastal counties and
waters.

Aside from rain chances overnight, tonight will be the first of a
couple of MUGGY nights out ahead of the main system expected to
arrive on Friday. Strengthening surface winds and CLOUD cover and
passing impulses will likely limit dense FOG development across the
region, however, the potential for low STRATUS will be high. Best
CHANCE of fog will be near the coast and e/se of a line from
Tallahassee thru Valdosta and Cross City and adjusted GRIDS
accordingly.

&&

.AVIATION..(thru 00Z Thursday)
Ongoing moist AIR advection from the gulf will keep ceilings in the
IFR/LIFR RANGE for most of the area overnight. Expecting fog to
impact all terminals starting at 3z near the coast and near 5z
further inland, with significantly reduced VIS between 1 to 2SM at
TLH,VLD,and ECP. 40kt winds near 2000ft will keep wind SHEAR wording
in the TAFs from 3z to 14z. Winds will pick up to around 20 KTS
gusting to 30kts region wide tomorrow afternoon and MVFR ceilings
will linger into the afternoon as well.

&&

.MARINE...MID eve buoys showing 10-15kts. winds expected to increase
from w-e overnight with se winds 15-20kt likely with SEAS building
to 4-5 feet offshore. thus will keep SCEC headlines.