National Weather Service Raw Text Product

133 
FXUS62 KTAE 300108
AFDTAE

Area Forecast Discussion
National Weather Service Tallahassee FL
808 PM EST Wed Dec 29 2021

.UPDATE...

The only changes to the previous forecast were to expand the
patchy fog wording to a larger portion of the area overnight and 
nudge low temperatures upward slightly. The best chance of fog is 
still across the southeast big bend. Otherwise, it will be a warm 
and muggy night for late December standards with lows in the mid 
to upper 60s, which is close to 25 degrees above average for this 
time of year.

&&

.PREV DISCUSSION [634 PM EST]...

.NEAR TERM [Through Thursday]...

Scattered showers are ongoing across the Tri-state area this 
afternoon, with the most robust activity focused mainly on the 
Panhandle thus far. Isolated thunder and some loosely organized, sub-
severe cell clusters have materialized. The moderately sheared and 
very moist environment remain marginally favorable for strong to 
severe convection over the next few hours. Gusty winds are the 
primary concern given the continued strong southwest flow and fast 
storm motions, though a brief, isolated tornado cannot be ruled out.

Convection shifts east and decreases tonight as instability wanes, 
though scattered showers appear to redevelop back west over the 
Panhandle and/or southeast AL overnight. Elevated southerly flow 
will keep muggy conditions in place, with low stratus and mild 
temperatures (low to mid 60s) expected through sunrise. Widespread 
and dense fog is not anticipated given that forecast winds are not 
sufficiently light enough. However, patchy fog/mist is possible in 
the southeast Big Bend and portions of the Suwannee Valley/I-75 
corridor.

A Marginal Risk (level 1/5) for severe weather is in place for much 
of the service area tomorrow. Convection looks to initially focus 
over the Wiregrass Region, then steadily shift east through the 
afternoon hours. The storm environment is expected to be similar to 
today - moderate shear, moist airmass, and strong low-level flow. 
However, without much of a forcing mechanism, storms are likely to 
only show loose signs of organization and be diurnally driven. Thus, 
the best severe potential may be during peak (albeit late-December) 
heating hours. Despite the cloud cover and rain chances, high 
temperatures are still forecast to be very warm (upper 70s to around 
80 degrees).


.SHORT TERM [Thursday night Through Friday night]...

The air mass will still be unseasonably warm and muggy. The air
mass will be weakly to moderately unstable. However, we will be
under a flat upper ridge, and larger scale lift will be lacking
after Thursday evening. This will period will feature a relative
lull, but not a dearth, of convective activity.


.LONG TERM [Saturday Through Wednesday]...

The highlight will be a sharp, strong cold frontal passage on
Sunday. Impacts preceding the front will include severe weather, 
possible coastal flooding, and rip currents. Marine hazards will
exist both preceding and proceeding the front, but they will peak
in the day following frontal passage.

The western U.S. trough will quickly kick east this weekend, 
racing across the Eastern U.S. on Sunday. This will represent a
major pattern change. Phasing of the northern and southern 
streams will take place, with a potent height fall/rise couplet 
passing across the Tennessee Valley and the southern Appalachians 
on Sunday. The southern extent of the strong upper dynamics may 
brush at least the northern portion of the forecast area, if not 
more. 

The air mass preceding the front is already unseasonably warm, 
muggy and moderately unstable. As the upper trough approaches,
500 mb winds aloft will increase to 60-70 kts, amounting to
1000-500 mb bulk shear of 50 knots or greater in the warm sector.
The sharpness of the front and the interaction with larger-scale
dynamics suggests a fast-moving line of thunderstorms or squall
line is the most plausible outcome. A line of storms in such a 
kinematic environment would likely come with some damaging wind 
gusts and an embedded tornado or two. Best guess on timing is that
the line would enter our western counties early on Sunday 
morning, then exit our eastern counties during the afternoon. With
4-5 days to go, such details are subject to adjustment.

Coastal flooding will also be possible around Apalachee Bay, as 
south and southwest winds increase. Already today, tide 
observations from Apalachicola and Cedar Key are running 1 to 1.5 
feet above tide table predictions, likely due to the days long 
duration and fetch of southerly breezes across the Gulf. 
ESTOFS guidance shows tides peaking around 2 feet MHHW, while 
probability- based PETSS guidance shows a reasonable worst case 
scenario (10 percent chance of exceedance) of 2 to 3 feet of 
inundation along the Dixie/Taylor shoreline. Of course, timing of 
peak surge values in relation to the normal cycle of high/low 
tides will matter. Bottom line is that a period of minor to 
moderate coastal flooding is shaping up. The period of greatest 
coastal flood concern will be around Saturday and Saturday night.

Once the front blows through on Sunday, a sharply colder air mass
will quickly arrive. Daytime temperatures will fall off quite a
bit on Sunday as colder air arrives. A light freeze is possible
over much of the area on Monday and Tuesday mornings, with a
harder freeze possible over southeast Alabama and near the 
Chattahoochee Valley. 

Low-level flow will become easterly on Tuesday, ushering in some
modified air with warming Atlantic influence.


.AVIATION...
[Through 00Z Friday]

A weakening band of showers from near ABY to BGE continues sliding
NE. Through the night, cigs will fall to IFR for all TAF sites, 
but vsbys should remain at or above MVFR. VLD has the best chance 
for MVFR vsbys. Isolated showers may develop overnight near ECP 
and DHN, but should wait until sunrise near TLH and ABY. Scattered
thunderstorms, some possibly strong, will develop late morning 
into the afternoon, generally moving E/NE. Outside of storms, 
gusty S/SW winds are expected (up to 20 kt.) and cigs improve to
MVFR by the afternoon.


.MARINE...

High pressure over and east of the Bahamas will continue moderate
to fresh southerly breezes through Saturday morning. Southerly
breezes will freshen and clock around southwesterly later Saturday
and Saturday night, in advance of a sharp and strong cold front
that will blast across the waters on Sunday. Behind the front,
strong to near-gale northwest breezes are forecast through Sunday
night, gradually easing and clocking around on Monday.


.FIRE WEATHER...

A warm, humid and breezy pattern will persist through Saturday.
Showers and a few thunderstorms with gusty winds are possible each
day. A strong and sharp cold front is forecast on Sunday. It
should be preceded by a line of strong to severe thunderstorms,
then followed by a sharp wind shift and the sudden arrival of a
continental polar air mass.


.HYDROLOGY...

Freshwater flooding is not expected for the next 7 days.
Thunderstorms will contain intense rainfall rates, but dry weather
since early November means flash flood guidance values are high.
No river flooding is forecast. 

Minor to moderate coastal flooding is possible around the shore of
Apalachee Bay around Saturday and Saturday night. See the Long
Term discussion above for more.


.SPOTTER INFORMATION STATEMENT...

Spotter activation is not requested. However, spotters are always
encouraged to safely report significant weather conditions when they
occur (while following all local, state, and CDC guidelines) by
calling the office or tweeting us @NWSTallahassee.

&&

.PRELIMINARY POINT TEMPS/POPS...

Tallahassee   67  79  66  79  66 /  20  60  20  20  10 
Panama City   67  76  66  76  67 /  30  70  30  30  30 
Dothan        67  79  66  79  67 /  50  80  20  30  30 
Albany        68  81  67  80  67 /  40  70  20  30  20 
Valdosta      66  80  66  80  64 /  20  40  20  20  10 
Cross City    64  80  65  77  63 /  10  30  20  10  10 
Apalachicola  66  75  65  75  65 /  20  50  20  20  20 

&&

.TAE WATCHES/WARNINGS/ADVISORIES...
FL...High Rip Current Risk until 7 AM EST /6 AM CST/ Thursday for 
     Coastal Bay-Coastal Franklin-Coastal Gulf-South Walton.

GA...None.
AL...None.
GM...None.
&&

$$

UPDATE...DVD
NEAR TERM...IG3
SHORT TERM...Haner
LONG TERM...Haner
AVIATION...Young
MARINE...Haner
FIRE WEATHER...Haner
HYDROLOGY...Haner