AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
648 AM EST Mon Nov 12 2012

.NEAR TERM [Today]…
LOW level MOISTURE has increased across the region overnight.
However increasing clouds with the approaching system has killed
chances of FOG so will update to drop fog from GRIDS.

The large scale longwave pattern remains highly amplified yet
progressive with ridging over WRN most states, troughing EWD to
ERN seaboard and ridging over extreme Wrn Atlc. TROUGH axis from
524dm low over N Dakota/Canadian border with axis down Ern Great
Plains. At surface, HIGH gradually retreating Ewd along Atlc
seaboard but still ridging strongly SWWD from offshore New England
to the Ern Gulf of MEX maintaining moderate ELY winds below
SUBSIDENCE INVERSION across local area. A cold FRONT is crossing
the MS River accompanied by showers and ISOLATED thunderstorms.
However, much of the activity is post-frontal and the CONVECTION
has been weakening considerably overnight.

During the next 24hrs, the upper trough will gradually lose
AMPLITUDE with the SRN end flattening AS primary SHORTWAVE helps
lift trough and most of assocd DYNAMICS/lift E/NE towards the MS
Valley today and OH Valley/Great Lakes region THRU tonight. Still,
this will essentially end any lingering influence of Ern RIDGE. All
this will serve to drive cold front SEWD albeit in a weakened and
slower form. Front moves across WRN TN/MS around SUNRISE then across
local region W-E during the EVE exiting SE Big Bend before
sunrise Tues. The tight GRADIENT of recent days will slacken with
the VEERING winds assocd with the approach of the front.

The onset of RAIN will be slow in coming with much of it along and
just behind the front as STRATIFORM rain with a rather sharp NW-SE
POP gradient. Models agree in a gradual weakening of rain band as
main HEIGHT falls lift more NEWD yielding increasingly thinning
moisture axis. In fact, in spite of forecasted nearly unidirectional
WIND profiles near the front, thermodynamic environment is
unimpressive and the shallow post-frontal nature of the
PRECIPITATION and lack of UPSTREAM LIGHTNING translate to limited
TSTM potential. Latest 21Z RAP13 shows surface CAPE restricted to
wrn waters and adjacent coastlines, and even here, BRN only 5,
BRN SHEAR only 25 m/s, 0-6 km shear only 30 and 0-3km SRH only about
100 m/s. This reflected in local confidence tool/CAM guidance which
show essentially zero CHANCE of THUNDER over land. The best rain
chances and any tstms over land still appear to be across SE AL, the
area closest to upper support and late this AFTN before DIURNAL
heating dies off, and in the eve. Overall QPF will remain low with
rain totals less than one half inch. Temperatures will remain above
NORMAL today, with highs in the MID to upper 70s.

&&

.SHORT TERM [Tonight Through Wednesday]…
Upper trough will deamplify further as it pivots into QUE early
Tues. The front will erode over our area tonight and wash out
across CNTRL FL on Tues. A 40-10% NW-SE POP gradient tonight
mainly before midnight.Cooler AIR will move in behind the front
tonight however cold air ADVECTION is limited so only expect lows
dropping into the upper 40s for portions of SE AL to the mid 50s
elsewhere.

In WAKE of front, a dry zonal FLOW aloft with continental polar
airmass over Ern CONUS expected for Tues and Wed. High PRESSURE
will extend from from the OH and TN valleys SWD to TX on Tues
building Ewd on Wed with cool NLY flow over local region. In
response, local gradients will again tighten. A weak shortwave
passes thru the region on wed thru wed NIGHT helping define a weak
trough that will drop across the area with some isentropic lift on
Wed but little in the way of rain will accompany it. On Tues and
Wed, highs will be much closer to normal, ranging from the mid 60s
in SE Alabama to the upper 70s in the far southeastern Big Bend.

&&

.LONG TERM [Wednesday Night through next Monday]…
The extended forecast will begin with predominately zonal flow
across the CONUS; a shortwave trough is expected to be centered
roughly over our forecast area – a feature that is currently evident
on water vapor satellite loops just approaching the Pacific coasts
of Oregon and northern California. The 12.00z ECMWF shows a more
amplified wave, while the 12.00z GFS indicates a very low amplitude
wave. Already the shortwave trough appears to be fairly vigorous
just off the west coast, and the 12.00z runs CMC and UKMET are in
fairly good agreement with the ECMWF. As such, we opted to include
rain chances Wednesday Night rather than follow the drier Gridded
MOS and MEX solutions.

After that, greater uncertainties arise regarding the evolution of
the synoptic flow pattern. The 12.00z operational runs of the ECMWF
and GFS both indicate the potential for a CUTOFF low to form near or
over the Southeastern US with wave breaking at the southern end of a
digging/amplifying trough by next weekend. Only about half the GFS
ENSEMBLE members indicate a similar pattern, so there are still
several possibilities beyond mid-week. For now we have adopted a
consensus approach with slightly below normal temperatures and
fairly dry weather until the models begin to converge on a solution.

&&

.AVIATION [through 12z Tuesday]…
The low STRATUS that models had been advertising has failed to
materialize thus far. Therefore, the 12z SET of TAFs is calling for
predominately VFR until the approach of a cold front in the west
with some MVFR possible later in the period at ECP, DHN, ABY with
some SCATTERED SHRA. Front and associated SHRA should weaken with
time, so things were kept dry and VFR at VLD and TLH for now.

&&

.MARINE…
With high pressure still camped out over the mid-Atlantic, another
SURGE in the easterly flow thru rest of overnight will justify
exercise caution headlines. Winds and SEAS will diminish during the
day today and remain below exercise caution levels, before becoming
offshore and increasing late tonight in the wake of a front. A
period of ADVISORY conditions are possible on Tuesday. Thereafter,
conditions will slowly improve. However, moderate northeast winds
are forecast to continue through the end of the work week.