Area Forecast Discussion
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FXUS62 KTAE 181400
AFDTAE

Area Forecast Discussion
National Weather Service Tallahassee FL
900 AM EST Tue Dec 18 2018

.UPDATE...

Temperatures are rising rapidly at this hour as the strong
inversion noted on the 12Z TAE sounding disspitates. This
will also quickly dissipate any patchy fog by 10 AM as the
diurnal boundary layer gets under way. Bumped up highs a
few degrees per 12Z TAE sounding mixed up to 2.5k FT AGL
with widespread 60s and some 70 degree values across the
region.

&&

.PREV DISCUSSION [617 AM EST]...

.NEAR TERM [Through Today]...
Any patchy fog that develops before sunrise will quickly improve
this morning. High pressure will continue to dominate today as a
surface high centered across the Great Lakes/Ohio Valley region
this morning slides to the eastern U.S. coast by this evening.
Conditions will continue to remain dry across the tri-state region
with near normal highs. Maximum temperatures this afternoon will
climb into the 60s.


.SHORT TERM [Tonight Through Friday Night]...
High pressure over the Mid Atlantic States will move out into the
Western Atlantic as a storm system begins to approach the region
on Wednesday. This system will present a low-end flood risk as
well as potentially significant coastal impacts starting Thursday
as the storm system moves over the region.

Cloud cover streaming over the region ahead of the storm system
tonight will help keep overnight lows from dropping into the 30s.
Instead, temperatures in the low to mid 40s are expected over the
inland areas.

On Wednesday, as the initial southern stream wave moves across
Texas and into the Western Gulf of Mexico, extensive cloudiness
will overspread the region and surface low pressure development
will commence off the coast of Louisiana. While it will take some
time for the local airmass to moisten, model guidance indicates
moist isentropic ascent across the western portions of the region
late in the day. As a result, will begin to increase PoPs at that
time. With all the cloud cover, high temperatures will struggle
to get out of the low to mid 60s.

As the southern stream shortwave moves up into the Tennessee
Valley Wednesday evening, a northern stream wave will rapidly
deepen as the pattern across the eastern CONUS amplifies. As this
larger trough digs deeper down into the Gulf of Mexico, a strong
surface low pressure area will strengthen over Louisiana and begin
to move NE. This configuration Wednesday night and into Thursday
morning will place our region in a very favorable area for strong
forced ascent yielding widespread rain. Given that there`s good
agreement in the track/placement of the surface/upper level
features, will increase PoPs to 90-100 percent from 06z Thursday
through 00z Friday.

After 00z Friday as the surface low rapidly moves up the Southern
Appalachians ahead of the high amplitude trough, the best forcing
for ascent shifts to the Atlantic coast, with any precip
associated with wrap-around moisture on the SW side of the storm
system. Will begin to taper rain chances off at this point,
especially into the daytime hours on Friday. With the system
staying fairly progressive, expect improving conditions across the
region after 18z Friday with skies potentially starting to clear
after 06z Saturday.

As far as impacts go, there still are some subtle differences in
placement of the heavier areas of precipitation and whether any
substantial warm sector can find its way further northward into
our region. Based on the 00z guidance package, it seems unlikely
for the surface warm front to pivot up into the Florida Big Bend.
Thus, any severe threat would be confined to the Central and
Southern Florida Peninsula.

Locally heavy rainfall will be a concern, especially across the
eastern half of the region where better favorable dynamics tend to
suggest a greater rainfall threat. Even so, due to the fast
movement of the system, rainfall amounts should average in the 1-2
inch range with isolated maximum totals up to 3 inches.

Coastal impacts could be substantial, particularly along the
western facing. Model guidance shows a 12-18 hour period of
strong southwesterly flow Thursday shifting to west-northwest into
Friday afternoon. This should be sufficient to rapidly build up
surf heights along the Florida Panhandle beaches west of
Apalachicola into the 7-10 ft range. These waves will be capable
of causing significant coastal erosion.

Minor coastal flooding is also possible in the Southeast Florida
Big Bend starting Thursday night and into Friday. Water levels
could rise to 1-2 feet above mean higher high water. Values in
this range typically result in flooding of boat ramps, and beach
access roads.


.LONG TERM [Saturday Through Tuesday]...
The long term period will be more tranquil with the large storm
system departing the Southeast by Saturday morning. With no storm
systems impacting the area through the long term period, expect
conditions to be fairly typical for late December with overnight
lows in the lower 40s and afternoon highs in the mid 60s on
Sunday. A warming trend beginning on Monday will result in
afternoon highs approaching the 70 degree mark for Christmas Day.


.AVIATION...
[Through 12Z Wednesday]

Fog has remained outside of the TAF sites this morning. Have
pulled the mention of fog this morning from the TAFs but it`s not
out of the question a site or two could see an hour or two lower
vsbys this morning. Otherwise, VFR conditions are expected with no
precipitation.


.MARINE...
Favorable marine conditions are expected into early Wednesday. By
Wednesday afternoon, winds and seas will be on the increase ahead
of an approaching storm system. Advisory level winds are expected
to begin Wednesday night. Winds and seas will build significantly
on Thursday afternoon and into Friday with a period of gale
conditions likely Thursday night through Friday afternoon. Winds
and seas will diminish quickly on Saturday.


.FIRE WEATHER...
Red flag conditions will not be met over the next few days as RH
values are above critical thresholds.


.HYDROLOGY...

There are numerous river locations across the eastern half of the
region still in minor flood. The Chipola River at Altha and the
Ochlockonee River near Thomasville are expected to drop below
flood stage later today. Further down the Ochlockonee River, water
levels will continue to rise with Concord cresting just below
moderate flood stage later this evening.

Within the Suwannee system, minor flood conditions are now
expected on the Withlacoochee River near Quitman (US-84) due to
another event above minor flood above Valdosta and increased
flows moving down the Little River. This in turn will result in
further rises down river into Florida, though Pinetta will stay
just below flood stage.

A extended period of river flooding is expected for our Suwannee
River forecast points from Ellaville through Wilcox over the next
seven days, even before taking into account any additional
rainfall. For now, it appears that all flooding within our portion
of the Suwannee Basin will be in the minor category.

For the incoming system on Thursday into Friday, widespread
rainfall amounts of 1-2 inches is possible with isolated maximum
amounts up to 3 inches, mainly in the eastern half of the region.
These amounts should present a limited flash flood threat, but the
heavier amounts will result in our faster responding rivers
(Chipola @ Altha, Ochlockonee, Upper Withlacoochee) rising into
the weekend, with minor flooding expected.


.SPOTTER INFORMATION STATEMENT...

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.

&&

.PRELIMINARY POINT TEMPS/POPS...

Tallahassee   69  42  66  54  66 /   0   0   0  90 100
Panama City   65  49  66  57  65 /   0   0  20 100  90
Dothan        66  44  62  51  63 /   0   0  20  90  80
Albany        66  42  63  51  64 /   0   0   0  90 100
Valdosta      67  43  66  54  65 /   0   0   0  80 100
Cross City    70  42  70  58  68 /   0   0   0  90 100
Apalachicola  67  49  65  59  67 /   0   0  20 100  90

&&

.TAE WATCHES/WARNINGS/ADVISORIES...
FL...None.
GA...None.
AL...None.
GM...None.
&&

$$

UPDATE...LF
NEAR TERM...Fieux
SHORT TERM...Godsey
LONG TERM...Godsey
AVIATION...Fieux
MARINE...Godsey
FIRE WEATHER...Fieux
HYDROLOGY...Godsey



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