AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE TALLAHASSEE FL
850 AM EST SAT Jan 21 2012


.NEAR TERM (REST OF TODAY THROUGH TONIGHT)...
MID/upper level SHORTWAVE IMPULSE continues to quickly translate
eastward from the lower MS valley toward the southern
Appalachians/Carolinas this morning. TROUGH axis now extends from
western TN to northern MS, noted by significant drying/SUBSIDENCE in
its WAKE over AR/northern LA. At the surface, the cold FRONT is
aligned ahead of the upper trough axis from eastern TN, southwest
through northern AL/central MS.

Large scale forcing/synoptic ascent ahead of the upper trough
combined with surface focus, and a general WAA regime ahead of the
cold front is forcing a solid line of CONVECTION over north-central
AL, and more SCATTERED variety convection further south and east
across AL/GA.

A large TORNADO WATCH box remains in effect just to our north across
central AL/GA related to this convection. SPC continues to OUTLOOK a
slight risk of severe weather co-located with this watch and also
extending a bit further south into portions of our SE AL/SW GA
zones.

The location of this slight risk zone still appears appropriate
after analyzing the latest output from our ENSEMBLE suite of CAM
(convective allowing models). Good agreement among these models
showing the potential for organized and rotating updrafts in the
vicinity of our far northern zones (mainly along the north of a line
from Dothan to Albany) later this morning through early this
evening. Will continue to monitor, but it does appear that the
window for the best severe potential will close off fairly early
this evening AS the shortwave impulse and resulting synoptic
forcing/SHEAR profiles shift past our area. With this quick exit of
the most favorable conditions, the potential to support severe
thunderstorms further south, especially along and south of the I-10
corridor appears LOW. However, will continue to monitor trends in
case the threat area needs to be briefly adjusted south. Either way,
the low level JET will be east of our area by 00-02Z with upper
HEIGHT rises/anti-cyclonic FLOW building in from the west. Therefore
some POPS will remain in the forecast overnight, but the threat for
severe weather looks to be over shortly after dark.

The forecast emphasis by later this evening will have shifted from
severe weather potential to dense FOG potential. Appears that a very
favorable setup for a dense fog event is in the making across a vast
majority of the forecast area. The cold front will be stalling over
or just north of our AL/GA zones tonight, allowing a continued
moist/southerly flow off the Gulf of Mexico. CURRENT forecast
dewpoints crossing the nearshore waters tonight are 2-5 degrees
higher than the surface water TEMPS. This is a good setup for
ADVECTION fog to move ashore/spread inland. Combine this with
an already favorable setup due to the general NVA/subsidence
overhead in the wake of the shortwave, and dense fog is a good bet.
All available HI-res guidance are picking up on this potential, and
the SREF probabilities for fog are very HIGH. The potential for
dense fog should SET in fairly early...by 03-05Z south of the I-10
corridor and expand quickly inland after midnight. Will continue to
highlight this potential in the GRIDS for the morning update.

&&

.MARINE...
Southerly winds will prevail through Monday along the western edge
of surface high PRESSURE. A weak front will pass over our coastal
and offshore waters late on Monday allowing winds to shift to the
north, and eventually to the east as high pressure builds in north
of our area. Winds and SEAS are not expected to increase
significantly with the passage of the front. At this time, no
headlines are expected through mid-week.

&&

.AVIATION (THROUGH 12Z SUNDAY)...
Areas of IFR VIS/CIG should slowly lift through 15Z. Scattered
showers and thunderstorms are expected to develop into our NW areas
by early afternoon. South to southwest winds will increase during
the day with frequent gusts over 20 knots. There remains a threat
for ISOLATED severe storms around DHN and ABY. THUNDERSTORM activity
should diminish during the early evening, but will quickly be
replaced by a potential WIDESPREAD fog event, which is expected to
develop earlier in the NIGHT and be more widespread than what we are
see this morning. The potential appears quite high at this point for
a widespread IFR or lower event at all terminals. The setup is
favorable for early fog development for KECP and KTLH, possibly
before 03-04Z, with fog rapidly spreading inland after midnight.