Special Weather Statement, NWS Tallahassee, FL

Area Forecast Discussion
National Weather Service Tallahassee FL
333 AM EST Tue Nov 29 2016

.NEAR TERM [Through Today]...

A series of shortwave troughs will continue to swing through the
deep positively tilted trough over the northern Plains as it moves
toward the upper Mississippi valley today. As these shortwave
impulses lift quickly off to the northeast, much of the energy
driving this system will become stretched and pull northward.

A well defined line of storms along a surface trough, just ahead of
the surface front, can be seen on regional radar imagery. The band
stretches across northern GA, central AL, southern MS, and
southeastern LA. Local hi-res guidance shows these storms will
approach our northeastern zones this morning, but dissipate in the
afternoon hours as the upper level forcing shifts northward and the
surface front stalls north of our area over the mid-Mississippi
valley. PoPs are in the 40-60% range northwest of a line from Panama
City, FL to Albany, GA for the morning, falling to about 30-40% in
the afternoon. Southwest of this line, chances for storms remain 30%
or less all day.

.SHORT TERM [Tonight Through Thursday]...

By this evening, the essentially full CONUS trough will have a
continuous channel of +PV stretching along the Rockies, through
the Southern Plains, and northeast through the Midwest. Advection
will consolidate this channel into a more focused anomaly over
the Lower Mississippi Valley on Wednesday afternoon, lifting
through the Ohio Valley Wednesday night. On Thursday, a southern
stream wave will move through the Southeast and flatten the base
of the trough as it lifts into the northern stream.

At the surface, the cold front currently draped across the
Southeast will have moved back northwest into the Lower
Mississippi Valley in the strong southerly flow regime. As the
upper-level anomaly consolidates and moves eastward it will re-
energize the front and start moving it to the southeast again. The
front and associated convection will pass through the Tri-State
region Wednesday and Wednesday evening, eventually being cleared
out by the passing southern stream wave. Surface ridging will be
firmly in place across the local area on Thursday.

The SPC has outlooked just about our entire region in a Marginal
Risk for severe weather. This threat area stretches from the
Suwannee Valley through southeast Alabama and the Florida
panhandle. The greatest threat for severe weather will be early to
mid afternoon Wednesday, and along and west of a line from Albany
through Panama City. The main threat will be damaging straight
line winds, though the potential also exists for an isolated
tornado. As the line moves east through the day, it will enter an
environment with a more stable atmospheric profile. However, with
a considerable amount of shear still present, uncertainty exists
as to whether or not the severe potential continues east of the
aforementioned line. Due to that uncertainty, the Marginal Risk
area is as described.

For information on expected rainfall amounts, see the hydrology
discussion below.

.LONG TERM [Thursday Night Through Tuesday]...

Zonal flow aloft and surface ridging will prevail through
Saturday before the upper-levels amplify once again. This is also
where models begin to diverge in their evolution of the next low
pressure system. The ECMWF is a little more amplified and
progressive as opposed to the GFS. At this time it can be said
with some confidence that rain chances will return late in the
weekend and could last through Tuesday. Depending on the model, a
potential for severe weather could accompany this system as well.
Regarding temperatures, expect more seasonal temperatures on
Thursday and Friday, gradually taking a warmer turn with the
approach of the next system.

&&

.AVIATION [Through 06Z Wednesday]...

Strong and gusty winds from the south will continue through the
period as the pressure gradient tightens with an approaching frontal
system. Cigs will remain mostly MVFR, though may drop to IFR late in
the period. Guidance shows this most likely near TLH. Rain today
appears to be most likely near our northern terminals, i.e. DHN and
ABY.

&&

.MARINE...

Advisory level conditions (at least in seas) will continue through
today before subsiding to Cautionary levels through much of
Thursday. A return to Cautionary or Advisory level winds and seas
is possible with the approach of another low pressure system late
this weekend. Showers and thunderstorms should be expected through
Wednesday evening, with some strong storms possible along a front
Wednesday afternoon through evening.

&&

.FIRE WEATHER...

Marginally high dispersions (around 70 to 75) will be present across
the area today and tomorrow as will strong transport winds (20-25
MPH). Relative humidity values however will remain well above
critical thresholds. No red flag conditions are expected for the
next several days.

&&

.HYDROLOGY...

Through Thursday, widespread average rainfall amounts will range
from 0.5"-1" along and northwest of a line from Albany through
Panama City, and between 0.25-0.5" southeast of the line. With
the ongoing drought and low river levels, these amounts will bring
some limited relief but not threaten us with any flooding
concerns.

&&

.PRELIMINARY POINT TEMPS/POPS...

Tallahassee   79  69  79  58  68 /  30  10  50  50  10
Panama City   78  71  75  57  66 /  30  30  70  40  10
Dothan        79  69  76  48  64 /  50  30  80  30   0
Albany        80  67  77  51  65 /  40  10  70  50   0
Valdosta      81  65  80  59  68 /  20  10  30  50  20
Cross City    81  65  80  64  73 /  10   0  20  50  30
Apalachicola  77  71  76  61  68 /  20  10  50  50  10

&&

.TAE WATCHES/WARNINGS/ADVISORIES...

FL...High Rip Current Risk through late tonight for Coastal Bay-
     Coastal Franklin-Coastal Gulf-South Walton.

GA...None.
AL...None.
GM...Small Craft Advisory until 7 PM EST this evening for Coastal
     Waters From Ochlockonee River to Apalachicola Fl out to 20
     Nm-Coastal waters from Apalachicola to Destin FL out 20 NM-
     Waters from Suwannee River to Apalachicola FL from 20 to 60
     NM-Waters from Apalachicola to Destin FL from 20 to 60 NM.

&&

NEAR TERM...Moore
SHORT TERM...Harrigan
LONG TERM...Harrigan
AVIATION...Moore
MARINE...Harrigan
FIRE WEATHER...Moore
HYDROLOGY...Harrigan

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