Area Forecast Discussion
Issued by NWS
FXUS62 KTAE 130904
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
404 AM EST Fri Dec 13 2013
...A Brief Light Freeze is Expected Across Many Inland Areas Around
...Heavy rainfall likely Saturday and Saturday Night...
.Near Term [Through Today]...
Seasonable temperatures, scattered upper-level clouds, and no rain
are the highlights for today`s weather. All of this is made possible
by what can generally be characterized by zonal upper flow (locally)
and high pressure at the surface.
.SHORT TERM [Tonight Through Sunday]...
The large scale pattern commence tonight with a trough/storm system
moving rapidly Ewd across Cntrl/Srn plains with base in E TX. A
series of shortwaves/impulses will be ejecting Ewd from this system
towards TN V alley. Under WSW steering flow, mid and high clouds
will continue to thicken over local area helping to moderate
temps. At surface, low over TX/OK Panhandle moves across Lwr MS
Valley by sunrise with cold front extending Swwd into Wrn Gulf. High
pressure off VA coast with axis WSW across Gulf region. Patchy fog
is likely especially across S/Cntrl GA.
During the rest of the period, model guidance in relatively good
agreement. This upper system moves quickly EWD into the Ms River
Valley/Mid South and begin to dampen by Sat morning as initial
shortwave gradually deamplifies and moves up Appalachians Sat
afternoon with next shortwave ejecting Ewd from Srn Plains
and it will be this impulse that pushes surface front/lows our
way on Sat. The upper system shifts to the Atlc by Sun morning
with upstream ridging overspreading the region. At surface,
advancing trough/shortwaves will generate broad surface wave
vcnty LA late tonight into early Sat. Cold front extends SWWD
across Wrn Gulf and warm front extends Swd into Cntrl Gulf. This
wave along with weaker secondary waves lift slowly Newd near or
along front and across Cntrl GA Sat aftn then Newd up Atlc coast
Sat eve into the overnight hours. Assocd warm front lifts Nwd
across CWA during the day with cold front crossing ESE during late
eve. This movement places much of area in warm sector ahead of
cold front. Showers and isold embedded Tstms will increase in
both coverage and intensity ahead of low, Sat into Sat night.
With good moisture surging off the Gulf of Mex, and approaching
trough providing added forcing and more favorable jet dynamics,
the primary concern from Sat morning through late Sat eve is
persistent and locally heavy rainfall. Area PWATS increase to
around 1.8 inches by Sat eve. Second wave not progged to exit area
until late Sat, overrunning rain to continue into early Sun. QPF
guidance show rainfall amounts in excess of 2 inches. The Euro and
NAM are both indicating rainfall amounts in the 2 to 3 inch range
as well with this system across N FL and Srn GA which further
increases confidence in the upcoming heavy rainfall event. While
these are widespread totals, isolated maximum totals of 4 to 5
inches are possible, especially with the stronger storms.
The severe weather threat is much less certain. While deep layer
shear will likely be sufficient for organized severe storms, surface
based instability is anticipated to be relatively weak and most
storms should be elevated. Any severe threat should be confined to
areas mainly in N FL near the coast along and south of low, and
even then should only be isolated with winds the main concerns.
By Sat evening, the secondary impulse will start moving away
from the region, the available forcing for heavy rainfall will
continue to decrease as the area of showers and storms moves into
the southeast FL Big Bend. On Sunday, models in good agreement
that rapid cyclogenesis across NE Conus will favor progressive
nature of srn tail of front which should limit post-frontal rain.
High builds to our NW. Cooler and drier air with breezier NW flow
will begin to overspread the local area from NW- SE.
Ahead of low, expect highs Sat 70 to 75 dropping Sun to from mid 50s
SE AL to upper 60s SE Big Bend. Inland lows tonight around 50,
increasing Sat night to from low 50s SE AL to mid 60s SE Big Bend.
POPs tonight 30-0% W-E gradient, 90-50% on Sat (with heavy rain in
grids), 50-80% Sat night and 20-50% mainly morning POP on Sun.
.LONG TERM [Sunday Night through Thursday]...
At the start of the long term period, the frontal boundary will be
exiting the region slowly to the south with drier air slowly
moving in. High pressure eventually takes control of the pattern
across the region Monday through Wednesday. Afternoon temperatures
should be around normal values Tuesday and Wednesday, though
overnight lows look to be a few degrees below normal as the rather
dry airmass and nearby high pressure allow for a couple of good
radiational cooling nights. The high pressure will move east of
the region on Thursday with onshore flow developing ahead of the
next storm system.
VFR conditions and relatively light winds will likely prevail
through the TAF at all terminals. The only exception may be some
high-end MVFR at KECP after sunset.
Winds will decrease below advisory levels rest of overnight and will
veer to offshore and continue to decrease with the approach of the
frontal system through tonight. Winds will shift to offshore and
increase behind the front on Sunday. Expect periods of cautionary
level winds well offshore through Monday night. Light winds and low
seas are expected by Tuesday.
Relative humidity levels should remain above critical thresholds for
the next several days, with an abundance of rain expected Saturday
through Sunday. Thus, hazardous fire weather conditions are not
Widespread rainfall is expected over the weekend. Total QPF amounts
differ between the models. The GFS has QPF values in the 1-2 inch
range, while the ECMWF has several areas over four inches. Average
rainfall totals of 2 to 3 inches with localized amounts of up to
five inches are expected, which will result in rises on area rivers.
The best chance of localized flooding would be across the FL Big
Bend and adjacent GA counties...and especially if the gulf low and
assocd warm and cold fronts slow down. A Hydrologic Outlook (ESFTAE)
was issued overnight and a flood watch may be necessary for a
portion of the region later today.
.PRELIMINARY POINT TEMPS/POPS...
Tallahassee 65 52 72 60 63 / 0 10 90 80 40
Panama City 65 56 72 59 62 / 0 20 90 70 30
Dothan 60 49 70 54 56 / 0 20 80 60 20
Albany 63 50 70 55 60 / 0 20 90 70 30
Valdosta 65 49 73 60 65 / 0 10 80 80 60
Cross City 69 52 75 64 68 / 0 10 50 70 50
Apalachicola 64 57 71 63 66 / 0 10 90 80 40
FL...FREEZE WARNING until 8 AM EST /7 AM CST/ this morning for
Gadsden-Holmes-Inland Jefferson-Inland Walton-Leon.
GA...FREEZE WARNING until 8 AM EST this morning for Baker-Brooks-
AL...FREEZE WARNING until 7 AM CST this morning for Coffee-Dale-
Near Term/Aviation/Fire Wx...Harrigan