Area Forecast Discussion
Issued by NWS
FXUS62 KTAE 122039
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
339 PM EST Thu Dec 12 2013
...Heavy rainfall likely Saturday and Saturday Night...
.NEAR TERM [Through Tonight]...
High pressure, currently centered over Arkansas, will slide east and
be centered over the Carolinas by Friday morning. With clear skies
expected, should see reasonable radiational cooling conditions.
Whether or not the boundary layer decouples will have a large impact
on where low temperatures end up by morning. With the position of
the high, SE Alabama and SW Georgia will have the best chance to
decouple. Thus, these areas will have the best chance for a light
freeze. With durations right around 2 hours possible for these
areas, will issue a Freeze Warning. Across Florida, do not expect
winds to widely decouple, thus any freezing temperatures should be
very short in duration. Overall, given the recent performance of the
statistical guidance (cold bias), have chosen to go above those
values by several degrees for morning lows.
.SHORT TERM [Friday Through Saturday Night]...
After a cold and tranquil start on Friday, things will quickly
change as a storm system spreads rapidly eastward out of the
Rockies. Model guidance is in relatively good agreement with the
progression of this system developing across Eastern Texas on
Friday evening and moving quickly eastward into the Mid South by
Saturday morning. The initial shortwave with this system will
gradually deamplify and move into the Ohio Valley Saturday
afternoon. A trailing higher amplitude impulse will move into the
Southeast late Saturday afternoon and likely lead to the
development of a wave of low pressure along the surface frontal
boundary just west of our region. As this development occurs, a
considerable increase in the coverage and intensity of the showers
and storms should occur. The primary concern from late Saturday
morning through Saturday evening is for heavy rainfall. SREF probs
for rainfall amounts in excess of 2 inches are relatively high for
an event still beyond 48 hours. The Euro and NAM are both
indicating rainfall amounts in the 2 to 3 inch range as well with
this system across North Florida and Southern Georgia - which
further increases confidence in the upcoming heavy rainfall event.
While these are widespread totals, isolated maximum totals of 4 to
6 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.
The 12z NAM did bring a corridor of +65F dewpoints well into
South Georgia, but this seems overdone given that this system is
not especially strong. As a result, think the severe threat should
be confined to areas mainly in North Florida near the coast, and
even then should only be isolated.
By Saturday evening, the seconary 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 Florida Big Bend.
.LONG TERM [Sunday 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.
.AVIATION [Through 18Z Friday] With high pressure in place over
the region, expect gusty winds to diminish by sunset and remain
light through the remainder of the forecast period. Otherwise, VFR
conditions are expected through Friday afternoon.
Borderline advisory winds will continue over the offshore waters
through tonight before decreasing with the approach of the frontal
system on Friday and Friday night. Winds will shift to offshore
behind the front on Sunday and increase to cautionary levels
through Monday morning before decreasing Monday afternoon. Light
winds and low seas are expected by Tuesday.
Low level moisture will begin to increase on Friday ahead of an
approaching cold front. This will keep minimum humidity values in
upper 30s and 40s for Friday afternoon. By Saturday, showers and
thunderstorms will move into the region, with no fire weather
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 four to
six inches are expected, which will result in rises on area
rivers. A flood watch may be necessary for a portion of the
region on Friday.
.PRELIMINARY POINT TEMPS/POPS...
Tallahassee 32 65 54 71 61 / 0 0 10 90 90
Panama City 39 64 57 71 60 / 0 0 20 90 80
Dothan 32 62 51 69 55 / 0 0 30 90 70
Albany 31 62 52 69 56 / 0 0 20 90 80
Valdosta 34 65 51 72 61 / 0 0 10 80 90
Cross City 35 70 52 74 65 / 0 0 10 50 80
Apalachicola 41 64 57 71 64 / 0 0 10 90 80
GA...FREEZE WARNING from 4 AM to 8 AM EST Friday for Baker-Brooks-
AL...FREEZE WARNING from 3 AM to 7 AM CST Friday for Coffee-Dale-
GM...SMALL CRAFT ADVISORY until 8 AM EST Friday for Waters from
Destin to the Suwannee River between 20 and 60 nautical