AREA FORECAST DISCUSSION…UPDATED FOR AVIATION SECTION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
546 AM EST Thu Nov 15 2012

.NEAR TERM [Today and Tonight]…
The main forecast challenge for the next 12 hours will be how
resilient the STRATUS deck that currently envelopes the entire area
will be. Based on water vapor loops from 05-07z, we appear to be
entering the region of NVA and SUBSIDENCE in the WAKE of a potent
MID-upper level PV ANOMALY / SHORTWAVE TROUGH. The changes AS a
result of this were demonstrated on the 00z JAN (Jackson, MS) and
OHX (Nashville, TN) soundings relative to the 12z soundings from
both locations. The 00z soundings showed lowering of the subsidence
INVERSION with considerable mid-level drying. Meanwhile, the 00z TAE
SOUNDING showed a deep saturated layer up to about 8000 FT (750mb)
with a subsidence inversion up around 650mb. As mid-level drying and
subsidence increase this morning across the area, the stratus layer
should gradually get thinned and eroded through mixing of drier
mid-level AIR. How quickly that process occurs will have notable
impacts on the TEMPERATURE forecast.

The consensus of model guidance appears to be that by mid-late
afternoon, enough mixing will occur to erode the clouds south and
west of a EUF-VLD line. MET MOS and ECMWF MOS seem to capture this
best, so they were used for the HIGH temperature forecast. This
should lead to highs in the 60s SW of the EUF-VLD line, and mid-50s
to the NE of that. RAIN showers and some patchy DRIZZLE should end
from west to east pretty quickly this morning as the aforementioned
shortwave departs the area.

&&

.SHORT TERM [Friday through Saturday]…
Friday looks to be a dry day with a bit more sunshine than we will
have seen the previous two days. Continued northeasterly FLOW below
800mb will anchor a cooler air mass in place across the area. In
fact, some of the models show 850mb temperatures cooling from
Thursday into Friday. This should result in another day with below
NORMAL temperatures. For Saturday, a digging shortwave trough should
become CUTOFF over the Southeastern US from the main branch of the
JET stream. The approaching mid-upper level wave may lead to the
slow development of a frontal wave from the coastal Carolinas into
the northeast Gulf of Mexico. This scenario would probably lead to
some SCATTERED showers, mainly over the far eastern parts of our
area, as well as some of our coastal waters.

&&

.LONG TERM [Saturday NIGHT through next Thursday]…
The large scale longwave pattern that commences the period is
highlighted by trough with axis just off West Coast, ridging over
the SRN Plains EWD THRU E/CNTRL gulf, then split flow over ERN most
CONUS with ridging over NRN states, and shortwaves DEEPENING trough
over SRN states and NE Gulf with cutoff LOW invcnty of local area
and dry NW/W flow overspreading local area. At surface, strong high
over Que with RIDGE axis SWWD across entire Gulf region.

During the rest of the period, as initial upper srn stream shortwave
exits EWD shunting trough offshore Sun into Sun night, weak upper
ridging or quasi-zonal flow takes hold as a drier airmass will
continue to overspread the region from NW-SE. At surface, ridge
holds while a low develops under upper trough off SE Coast by Sun.
This combination providing N/NE low level local flow with tightening
GRADIENT (so FOG unlikely but low stratus possible) and further
dries our local area. EURO and GFS continue to diverge by Sun night.
Both show drying trend TIL at least Tues but former more aggressive,
farther south and stronger with cutoff low and thus slower in moving
trough off ERN seaboard and in pulling surface low NEWD. Conversely,
GFS which reabsorbs low into open wave, begins and ends local
MOISTURE earlier. So, overall confidence in forecast not high and
will blend.

Models show next trough exiting Rockies on Mon, MS Valley on Tues
and into SE region on Wed.  Assocd weak upper level shortwave moving
EWD ahead of trough shifts zonal flow to weak cyclonic late Tues
into Wed,and helps erode local surface ridge with an increase in
clouds. This time GFS more bullish with another trough and surface
REFLECTION invcnty local region yielding next CHANCE of rain over NE
Gulf while EURO rather dry. Again until I see some consistency will
favor blend and show modest uptick in PRECIPITATION.

Forecast continues to be mostly dry one and will go with NIL POPS
thru Tues, then WDLY SCT Tues night and sct on Wed. MIN TEMPS will
hover around CLIMO SAT thru Mon nights before rising to slightly
above climo Tues and Wed nights. MAX temps to run several degrees
below normal to commence the period, then around climo for rest of
period. AVG inland min/max is 45/70 degrees.

&&

.AVIATION [through 12 UTC Friday]…
Updated at 545 AM EST-
Although the disturbance responsible for the rain will pass the
area by this morning, moist NELY flow will make low clouds slow to
mix out thru the day. So OCNL drizzle will linger Ern areas and
persistent low ceilings will continue thru the day and for Ern
terminals past SUNSET. In general, skies will very slowly scatter
out to VFR from west to east so MVFR conds much of the day with LCL
IFR KVLD into this morning with rain clearing from west to east.
AFTR 06z, expect MVFR cigs to again redevelop except at KECP with
possible IFR towards SUNRISE at KVLD.

&&

.MARINE…
With surface high PRESSURE expected to dominate the weather pattern
over the eastern US through early next week, offshore flow is
expected to continue for the foreseeable future. From Friday night
through early Monday morning, there will be chances for SCEC winds
(or perhaps even borderline SC.Y winds well offshore). The strongest
winds will be with typical NOCTURNAL increases from about 03-12z.

&&

.FIRE WEATHER…
HUMIDITY values are forecast to remain well above critical levels
through Friday, with no red flag conditions expected into the middle
of the upcoming work week.

&&

.HYDROLOGY…
Gauge-adjusted QPE suggests that RAINFALL amounts across the area
were generally less than 0.10″ over the past 24 hours, with little
additional rainfall expected in the upcoming 24 hours. Therefore, no
significant river rises are expected.