Severe Thunderstorm Warning 468, NWS Tallahassee, FL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
741 PM EST MON DEC 21 2015

.Update...
No significant changes were made to near term forecast. Previous
discussion is below.

.Aviation...
[Through 00Z Wednesday]...

Expect IFR ceilings and heavy rain tonight for ECP and DHN. Expect
IFR ceilings and heavy rain by morning for TLH and ABY. Heavy rain
will move into the region overnight and will persist on Tuesday.
MVFR ceilings are likely on Tuesday, but heavy rain will restrict
visibility greatly.

&&

.Prev Discussion [355 PM EST]...

.Near Term [Through Tonight]...

A large, broad trough covering the entire country (and more) is
resulting in southwesterly flow aloft locally. Within the
southwesterly flow, a southern stream shortwave is expected to move
along the northern Gulf Coast beginning tonight. The long fetch of
tropical moisture is providing the Southeast with PWATs of 1.5-2",
around 1" above normal. As the upper level wave links up with
ongoing low-level isentropic ascent tonight, the coverage and
intensity of rain will increase. On average, rainfall amounts around
2 to 3 inches are expected across extreme southwest Georgia and west
of the Apalachicola and Chattahoochee rivers. Isolated higher
amounts in this area could range from 4 to 6 inches. Elsewhere,
around an inch is more likely. Although an isolated strong storm
cannot be ruled out along the Panhandle coast tonight, the limited
severe weather threat should remain out over the water. Lows tonight
will likely be in the 60s area-wide.

.Short Term [Tuesday Through Wednesday Night]...

Models continue to be consistent with the set up for the heavy rain
event this week as several impulses move through the broad trough.
Expect the first round of rain to continue through Tuesday as the
first short wave moves through. A lull is possible Tuesday
afternoon, before the next round of rain starts Tuesday night and
continues through Wednesday. Models guidance is consistent with
widespread heavy rain. The forecast for Tuesday through Wednesday
reflects this with 60-80% PoPs for the area with the exception of
the Big Bend, where PoPs will be 40-50%. The main concern for
Tuesday and Tuesday night will be heavy rain and flooding. As the
850mb jet moves over the region and wind shear increases, strong
to severe storms will be possible on Wednesday in addition to the
flooding threat. SPC has the area in a marginal risk both Tuesday
and Wednesday. Rainfall totals through Thursday will range from
1 to 2 inches in the southeast Big Bend to 5 to 9 inches in
southeast Alabama and the western panhandle. The flash flood watch
will remain in effect until 7am Wednesday morning. Highs will be
in the 70s with lows in the upper 60s.

.Long Term [Thursday Through Monday]...

While not as heavy as Wednesday, rain chances will linger through
Thursday with the highest chances in southeast Alabama and the
western Panhandle. Ridging will build in on Friday, limiting PoPs to
20 percent through the weekend. By Monday a large low pressure
system over Texas will start to move northeast and the associated
cold front will approach our area. PoPs will increase and will be in
the 20-30% range for Monday. Temperatures will be well above average
through the period and will even approach several records. Highs
will be in the upper 70s to low 80s and lows will be in the 60s.

.Marine...

Heavy rain and thunderstorms are likely through Thursday.
Southeast winds will approach 20 knots by Wednesday when seas will
seas will increase to 3 to 5 feet.

.Fire Weather...

A soaking rain is expected for the next few days beginning tonight.
No fire weather concerns.

.Hydrology...

A potentially significant flood event looks to be
setting up over the next couple of days across the region. Model
guidance has been consistent that two batches of moderate to
heavy rain will move over the area starting late tonight and
continuing through Wednesday night. Average storm total amounts
across the western areas are expected to be in the 5 to 9 inch
range with lesser amounts of 4 to 7 inches east of the river.

While the event will be separated into two distinct events, with the
airmass being so moist, it's possible that each grouping of storms
could produce a localized flash flood threat. Thus, for simplicity
have issued a flash flood watch that spans both events.

From a river perspective, the most vulnerable area is across the
Choctawhatchee and Pea River Basins in Southeast Alabama and the
Florida Panhandle given the above normal streamflows present at
several of the gauges in these areas. Further to the east, the river
flood threat isn't as significant in the ACF basin, however,
ensemble guidance suggests at least some potential for minor
flooding in the creeks above Albany and possibly down to Bainbridge.

Lighter amounts (and relatively) lower flows in place across the
Ochlockonee and Withlacoochee River Basins should keep the overall
river flood threat lower in these areas.

&&

.Preliminary Point Temps/PoPs...

Tallahassee   62  73  68  76  68 /  90  80  70  80  60
Panama City   64  73  67  75  70 /  90  80  80  80  70
Dothan        59  72  65  74  67 /  90  80  80  90  60
Albany        60  72  65  75  67 /  90  80  80  80  50
Valdosta      62  75  67  77  67 /  60  70  60  60  40
Cross City    65  78  69  80  69 /  30  40  50  50  40
Apalachicola  66  72  68  74  69 /  90  80  70  80  60

&&

.TAE WATCHES/WARNINGS/ADVISORIES...
FL...Flash Flood Watch through Thursday morning FOR Calhoun-Central
     Walton-Coastal Bay-Coastal Franklin-Coastal Gulf-Coastal
     Jefferson-Coastal Wakulla-Gadsden-Holmes-Inland Bay-Inland
     Franklin-Inland Gulf-Inland Jefferson-Inland Wakulla-
     Jackson-Leon-Liberty-North Walton-South Walton-Washington.

GA...Flash Flood Watch through Thursday morning FOR Baker-Ben Hill-
     Berrien-Brooks-Calhoun-Clay-Colquitt-Cook-Decatur-Dougherty-
     Early-Grady-Irwin-Lee-Miller-Mitchell-Quitman-Randolph-
     Seminole-Terrell-Thomas-Tift-Turner-Worth.

AL...Flash Flood Watch through late Wednesday night FOR Coffee-Dale-
     Geneva-Henry-Houston.

GM...NONE.
&&

NEAR TERM...HARRIGAN
SHORT TERM...WESTON
LONG TERM...WESTON
AVIATION...MCDERMOTT
MARINE...WESTON
FIRE WEATHER...MCDERMOTT
HYDROLOGY...GODSEY/WESTON