FXUS62 KTAE 180810

Area Forecast Discussion
National Weather Service Tallahassee FL
310 AM EST Mon Dec 18 2017

.NEAR TERM [Through Today]...

As an upper level cut-off low meanders near the Arizona-Mexico
border, a broad flat ridge will cover Florida and the eastern Gulf
of Mexico. A surface front just north of the region will move little
today. The forecast are will therefore be in a warm and humid air
mass for this time of year. Low clouds will be the rule for much
of the day and with the low sun angle, I am a bit concerned about
getting as warm as some of the guidance is suggesting. I went a
couple of degrees below a guidance consensus for max temps, closer
to the ECAM, but this still gives us 70s in most areas. After the
current patch of rain moves east and dissipates, PoPs during the
daylight hours will be highest across our northern zones, closer
to the front, and diminish toward the coast. Rainfall amounts will
be light. Some advection fog may begin to develop during the day
over the marine area. More on that below.

.SHORT TERM [Tonight Through Wednesday]...

A relatively strong 500 mb ridge over the Southeast will weaken
Tuesday night and Wednesday as a short wave trough (currently over
the Baja Peninsula) moves eastward across the Southeast. Until
then rain chances for our forecast area will be slight and
confined mainly to the northern parts of our area, on the fringes
of weak Q-G forcing and increasing deep-layer moisture. Rain
chances will increase Wednesday, especially across the FL
Panhandle, southeast AL, and southwest GA, where the greatest
concentration of large scale ascent and moisture will be. (PoPs
will range from 60% at Dothan to 30% at Tallahassee, and less than
20% at Cross City).

Although most of the upper-level height falls will be to our
north, 0-6km bulk shear values of at least 50 knots over our
forecast area would suggest at least some possibility of storm
organization. However, MLCAPE values will struggle to reach 500
J/kg. Thus with limited buoyancy and large-scale ascent, the
threat of isolated severe storms on Wednesday is low, and would
consist primarily of damaging wind gusts (40-60 MPH) or perhaps
a brief tornado, mainly north and west of Tallahassee.

Temperatures are likely to be well above climatology, despite
significant cloud cover during the daytime. Lows will be in the
lower 60s (climatology is lower 40s). Highs will be in the mid
70s (climatology is lower 60s).

.LONG TERM [Wednesday Night Through Monday]...

Rain chances will end quickly Wednesday night once the
aforementioned upper trough and associated surface baroclinic trough
move by, with only a slight drop in temperatures to close out the
work week. Considerable differences arise between the global models
by the weekend. The GFS brings a cold front slowly through our
forecast area and stalls it just to our south, with gradually
cooling temperatures and persistent rain chances through Christmas
Day. The ECMWF keeps the front well to our northwest, with
continued warm temperatures and fair weather. As usual this far
out, we have blended the solutions and get PoPs in the 20-30%
range, highs in the upper 60s (north) to mid 70s (south), and lows
in the 50s. Hopefully the models will trend toward the same
solution in subsequent forecast cycles.


.AVIATION [Through 06Z Tuesday]...

A few rumbles of thunder will occur in the vicinity of ECP at the
start of the TAF period. After a patch of rain moves through the
region, IFR ceilings will develop with drops in visibility to
follow. The IFR ceilings should persist through the daylight hours
along with some drizzle or sprinkles at times. It continues to look
like an advection fog will envelop all terminals tonight and we show
conditions deteriorating around 02Z. VLIFR conditions are certainly
possible everywhere tonight.



Relatively light south to southwest winds and lowering seas will be
the rule through Tuesday under the influence of a weak high pressure
system. Southwest winds will briefly increase on Wednesday as a
low pressure trough moves through the region, with light winds and
low seas returning Wednesday night and Thursday.



Relatively humid conditions will preclude most fire weather concerns
over the next several days. Dispersion values will be on the low
side today and tomorrow, but not quite low enough to warrant a
headline. Patchy fog is possible this morning, but a widespread,
possibly dense fog, is expected tonight.



The latest NOAA ESRL analog QPF (through Saturday), based on
Sunday's GEFS, shows QPF ranging from half an inch over portions of
southeast AL and south GA to a quarter of an inch or less elsewhere.
This is very close to WPC's latest 7-day QPF totals. This is an area
average, and isolated higher amounts are possible in deep
convection. These values would have little impact on the local river
system, and are unlikely to cause flooding.



Spotter activation is not requested. However, spotters are always
encouraged to safely report significant weather conditions when they
occur by calling the office or tweeting us @NWSTallahassee.



Tallahassee 75 61 76 60 76 / 30 10 10 10 30
Panama City 73 63 75 63 73 / 30 10 10 10 30
Dothan 71 59 74 62 74 / 60 10 10 20 60
Albany 70 59 72 61 74 / 50 20 10 10 60
Valdosta 74 62 75 60 75 / 30 20 10 10 30
Cross City 77 59 77 57 77 / 10 10 10 10 10
Apalachicola 73 62 74 62 74 / 20 10 10 10 20




SHORT TERM...Fournier
LONG TERM...Fournier
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