AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE TALLAHASSEE FL
842 PM EST Wed Dec 28 2011


Updated most recently for SYNOPSIS and Near Term sections.

.SYNOPSIS...A fairly potent MID-upper level SHORTWAVE TROUGH was
moving quickly east-southeast this evening through east Texas.
Ahead of the approaching wave, higher clouds were streaming into
the eastern Gulf Coast region. The lower levels of the ATMOSPHERE
across the region were very dry, though, AS sampled by the 00z
soundings. A weak surface HIGH PRESSURE was centered almost
directly on the forecast area with very light winds. Some west-
southwesterly return FLOW was beginning across parts of southern
Louisiana and Mississippi on the back side of the high, but deeper
LOW-level MOISTURE had not made any progress inland in those
areas. Therefore, despite relatively strong forcing for vertical
motion ahead of the approaching wave, limited moisture and weak
WIND fields underneath the low-level high pressure are expected to
keep RAIN chances generally under wraps in the short term.

&&

.NEAR TERM (Tonight)...Most of the near-term grid edits this
evening were focused around TEMPERATURE trends tonight, and then
POPS over the Gulf waters over the next 24 hours. As mentioned in
the "Synopsis" section, there is a potent PV ANOMALY moving into
southwest Louisiana at the moment. Objectively analyzed dynamic
TROPOPAUSE maps suggest that the 1.5 PVU surface could be as low
as 550-600mb with that wave. Therefore, it`s not surprising that
there is a decent amount of forcing for ascent (especially in the
middle and upper TROPOSPHERE) ahead of the wave. This is resulting
in some CIRROSTRATUS pushing in from the west, and IR satellite
suggests this could be fairly thick in spots. Therefore, the
radiational cooling process could be limited by the increased
CLOUD cover overnight. Low temperatures were kept fairly close to
the previous forecast, but FROST wording was toned down, and the
mention of freezing temperatures was removed from the HWO.

Changes to PoPs were made into Thursday, as high resolution model
guidance is insistent on SCATTERED showers developing late tonight
and then pivoting into the western sections of our coastal waters
tomorrow. These showers develop near a subtle surface trough from
near Mobile Bay south into the Gulf, and in an area of increasing
low-level moisture. Indeed, there appears to be some low clouds
(4000 FT ceilings) offshore of Mobile Bay stretching south into
the NC Gulf of Mexico. Some of the PoPs derived from high-res
guidance was as high as the upper "CHANCE" RANGE (40-50%), but we
opted to trend things up from a dry forecast to "Slight Chance"
PoPs (20%) for now. With models keeping most of the SHOWER
activity offshore, we kept rain chances over the water as well.

&&

.SHORT TERM (Thursday through Friday NIGHT)...Moving ahead to
Friday, several models hint at some moisture returning and even
some very light showers moving into the western Florida zones from
the Gulf. The 00z NAM was quite bullish and showed 30 to 50 PoPs
over portions of the panhandle. The 12z NAM backed off somewhat
and shows 20 to 30 PoPs. This seems overdone and have instead just
gone with a silent 10 POP for now and will wait for some more
model consistency before adding mentionable PoPs into the forecast
in that area on Friday. The pattern just does not look too
favorable for precip, and there is no real well defined upper
level shortwave forecast for Friday in that area.

Temperatures are expected to commence a slow warming trend through
the short term after tonight with highs near 70 LIKELY by Friday.


.LONG TERM (Saturday through next Wednesday)...The period will
start our dry and mild through the weekend with surface high
pressure to our east and near zonal flow aloft. MIN TEMPS will be
in the mid to upper 40s with highs in the lower 70s across most of
the forecast area. Prior runs of the GFS and ECMWF (Euro) showed
big differences in their handling of the next trough to amplify
into the east. While the GFS remains a bit more progressive, the
Euro has moved sharply toward the GFS and away from its prior
solutions of cutting off a huge upper low in the vicinity of the
southern Appalachians. This leads to similar timing for the cold
frontal passage, which is PROGGED for Sunday night into early
Monday. The GFS still shows a dry frontal passage, while the Euro
shows a band of frontal PRECIPITATION, which incidentally departs
well before it gets cold enough for anything but rain. Since the
Euro is trending toward the GFS, we will maintain our CURRENT
forecast of a dry frontal passage. However, we do plan on going
below the operational guidance for temps by a FEW degrees to
account for the fact that MOS tends toward CLIMATOLOGY that far
out and the Euro is much deeper with the trough. This all
translates into temps taking a tumble behind the cold FRONT. Highs
Monday will be near to a couple of degrees below NORMAL. Monday
night should see temps well down into the 30s with some areas
dipping below freezing. On Tuesday and Wednesday, we are calling
for MAX temps in the lower to mid 50s north and mid to upper 50s
south. Wednesday morning should see temps a couple of degrees
below freezing. Note that if the current Euro solution verifies
(with 850-MB temps some 8 to 12 degrees below zero), temps will be
significantly colder than currently advertised from Monday night
into Wednesday, certainly low enough for the area to see the first
WIDESPREAD hard FREEZE of the season. Stay tuned.


&&

.AVIATION (through 00z Friday)...VFR is expected to prevail through
the period with some high CIRRUS and light winds. Current
satellite analysis and offshore observations are showing a 3500 ft
cloud deck over the northwestern Gulf of Mexico. This cloud deck
is expected to affect KECP and KDHN during the early morning
hours. No significant ceilings are expected however.


&&

.MARINE...As high pressure builds eastward across the Gulf, winds and
SEAS are expected to remain light through the weekend. Winds and
seas may elevate to ADVISORY levels early next week after the
passage of the next cold front.


&&

.FIRE WEATHER...Much cooler and drier AIR is building into the region
behind the cold front that passed through the area Tuesday
morning. The afternoon relative HUMIDITY is forecast to drop near
35 percent across parts of the Florida big bend and panhandle
today, Thursday, and Friday. However, red flag conditions are not
expected to occur as durations of low relative humidity are
expected to be short.