AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
320 AM EST Wed Feb 8 2012


.SYNOPSIS...
07Z water vapor and H4 RUC analysis continues to show a rather
complex upper level pattern across the CONUS this morning. REX block
configuration from 24 hours ago over the western portion of the
continent has broken down, with the closed upper LOW over Colorado
now having opened up and become progressive. This TROUGH and any
significant associated forcing will pass north of our region today.
We continue to see an ACTIVE southern stream FLOW with abundant
MID/upper level energy in the form of HIGH level CIRRUS streaming
northward over the Gulf of Mexico.

At the surface, forecast area resides in a region of weak GRADIENT
between 1035mb high PRESSURE over the central Plains, and a surface
trough in place across the southern FL Peninsula/FL Straits.
Weak/subtle cold FRONT is analyzed slowly approaching our area
across AL. This front is better defined above the surface, but
should at least result in a somewhat drier low level airmass in its
WAKE over the next couple of days. Regional radars do show a FEW
showers up into central AL/Northern GA in closer proximity to the
passing synoptic forcing. However AS mentioned above, this
sufficient forcing will remain to our north and keep SHOWER chances
out of our forecast.

&&

.SHORT TERM (TODAY THROUGH FRIDAY)...
Today,
Mid/Upper level SHORTWAVE passes from the TN valley this morning to
the mid-Atlantic coast this evening. Atmospheric momentum associated
with this energy will be enough to pass a weak cold frontal boundary
through the forecast area by mid/late afternoon. This will be an
uneventful frontal passage with only some clouds and a slight WIND
shift to mark its arrival. Overall, will be a pleasant February day
with filtered sunshine and high temperatures ranging from the upper
60s north to the lower 70s south.

Tonight,
Dry and somewhat cooler NIGHT upcoming to what has been experienced
lately. The drier airmass will allow temperatures to FALL into the
upper 30s to lower 40s for much of the area. The high CENTER will
still be well to our NW keeping the gradient fairly tight. With this
in mind, don`t anticipate much CHANCE of any normally sheltered
areas de-coupling and getting much colder than is currently
forecast. Therefore, temperatures and dewpoint depressions should
stay above the level of a FROST threat.

Thursday/Thursday night,
Little change in the forecast with any significant northern stream
energy remaining well to our north. High level clouds will LIKELY be
on the increase once again by the end of the day as southern stream
JET energy re-develops along the northern Gulf Coast. Plenty of dry
AIR in the lower levels will keep RAIN out of our forecast with high
TEMPS reaching up into the 60s. Surface ridging will SET up just to
our north Thursday night which will bring the potential for some mid
30s temps inland, and a resulting frost potential. However, some
uncertainly remains regarding the amount of mid/high level clouds
that will be overspreading the area. Impressive southern stream jet
energy suggest we will see the cirrus. Even high level cloudiness
can sometimes disrupt the radiative process and help keep temps
warmer than expected. This portion of the forecast will need to be
monitored closely for those with sensitive outdoor vegetation.

Friday,
Uncertainly is beginning to increase by the end of Friday with
regards to energy propagating across the southern Plains and
northern Gulf coast. GFS is showing a scenario in which much of this
energy is absorbed by a large cut-off low near the California Baja
region. ECMWF/Canadian are much more aggressive, and allow the
majority of this shortwave energy to bypass the upper low into the
southern Plains. These models offer solutions that are potentially
wetter for our western zones by Friday evening, and for all of our
zones Friday night. Tough call on this one, but out of respect for
the ECMWF will add slight chance POPS to the GRIDS beginning Friday
afternoon in the far west, and for all zones Friday night. Should
the ECMWF/Canadian solution be the correct trend, then these rain
chances would need to be adjusted upward in future forecast
packages.

&&

.LONG TERM (SATURDAY THROUGH NEXT WEDNESDAY)...
The complex and generally messy large scale pattern is expected to
remain so during the forecast period, while undergoing some
RETROGRESSION, with axis of the MEAN RIDGE over the western U.S.
shifting westward into the eastern Pacific, and the large polar
VORTEX over eastern Canada also evolving westward. The main effect
will be to broaden the mean trough westward across the CONUS,
resulting in a positive tilted trough axis across the Intermountain
West, and a nearly zonal flow eastward across the eastern half of
the country. The southern portion of the stream will remain quite
strong. A series of short waves will drop southward into the mean
trough axis over the Intermountain West, then weaken as they HEAD
rapidly east or northeast across the eastern U.S. As always, the
devil is in the details when it comes to the forecast for he
Tri-State Area. The GFS and Euro continue to diverge predictably
towards the end of the period, in how they handle the short waves
dropping into the mean trough position. The Canadian and EURO are in
better agreement, showing more short wave energy in the southern
stream, which gives me some confidence, and a blend of the two
solutions seems the way to go. Friday night and Saturday short wave
energy will be moving eastward across the eastern U.S. pushing a
cold front well to the south across the southern Florida peninsula,
bringing at least a slight chance of rain, and a SURGE of colder
drier air behind it across the southeast U.S. Temperatures may drop
to near or a little below freezing in some areas on Monday morning.
Then expect a fairly rapid rebound in temperatures by mid week,
along with an increasing chance of rain, as the next short wave
rounds the bottom of the trough and heads northeast. Temperatures
will start out near NORMAL on Saturday, then drop below normal
Sunday and Monday, then trend back to above normal by Wednesday.

&&

.MARINE
A weak cold front will cross the forecast area today. The gradient
behind this front will increase and result in near ADVISORY level
northerly winds tonight through Thursday morning. A surface ridge
will slowly build down from the north later Thursday into Friday
which will act to drop winds and SEAS back down below headline
criteria. Another period of cautionary to advisory level northerly
flow looks to develop during the upcoming weekend.

&&

.AVIATION (THROUGH 06Z THURSDAY)...
VFR conditionsĀ  will continue across the Tri-State Area through the
forecast period and beyond, with patches of cirrus occasionally
streaming across the area. Although a drier airmass has spread into
the region, good nighttime cooling will result in temperatures
dropping to near the DEW point temperatures in some areas, allowing
for the formation of someĀ  MIST before daybreak. The mist, in
combination with some lingering SMOKE, will produce patches of MVFR
visibilities primarily across south central Georgia before SUNRISE.

&&

.FIRE WEATHER...
Drier air is spreading across the Tri-State Area, and relative
humidities across inland portions of Florida will drop to at or
below 35 percent for several hours this afternoon, along with
relatively high dispersions. However, dispersions are not expected
to be quite high enough to warrant a Red Flag WATCH or WARNING, and
ERC values will continue relatively low. Thursday will remain dry,
with longer periods of critical relative HUMIDITY values, while
dispersions are expected to be a little lower. However, ERC values
are currently expected to remain below critical levels, so while
conditions for Thursday afternoon should be closely monitored, there
are no fire weather concerns at this time.