Area Forecast Discussion
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658
FXUS62 KTAE 202147
AFDTAE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
447 PM EST Thu Nov 20 2014

...Heavy rainfall and strong storms possible late Saturday night
into Sunday...

.Near Term [Through Tonight]...
High pressure centered across the Southern US will remain in place
through the night allowing for one last night of good radiational
cooling conditions. Satellite imagery does show the increase of
mainly upper level cloudiness, and this may limit some of the
cooling. Moreover, surface data from 21 UTC show that near surface
moisture levels have increased markedly in the last 24 hours, with
surface dewpoints back into even the lower 40s for portions of the
Florida Panhandle. The driest airmass though still remains over
the Florida Big Bend, thus with the very favorable radiational
cooling conditions, will indicate one last night of freezing
temperatures - though only 30 to 32 degrees in the Florida Big
Bend. Elsewhere, we should manage to stay above freezing.

.Short Term [Friday Through Saturday Night]...
Friday will be a transitional day as high pressure moves eastward
into the Atlantic and a developing storm system moves eastward
across Texas toward the Western Gulf of Mexico. By Saturday this
storm system will be approaching the Western Gulf with a large
area of isentropic ascent ahead of it leading to the development
of widespread cloud cover and rain across the Gulf. The best area
of lift will shift quickly northward as the upper level system
moves into the Mississippi River Valley on Saturday night. Expect
rain to increase quickly across the region after sunset with
moderate to heavy rain moving in late Saturday night. On the order
of 1.5 to 3 inches of rain, particularly across western areas
looks possible on Saturday night with lower amounts off to the
east. The severe thunderstorm threat doesn`t appear as significant
as it did yesterday. The Euro and GFS both show the warm front
reaching the coast around 12z Sunday - slower than in earlier
runs. Thus, the severe threat Saturday night may be confined to
the coastal waters or perhaps right along the immediate coast. In
the short term period, heavy rainfall is the primary threat.

.Long Term [Sunday Through Thursday]...
At the beginning of the long term period, extensive cloudiness
with widespread rain will be ongoing across the forecast area. The
best synoptic forcing for precipitation will be shifting north of
the area after about 18z on Sunday. There is some concern that a
squall line may move through the region once the warm front
retreats far enough northward, though the 12z runs this afternoon
have difficulty keeping enough forcing back in the warm sector to
generate these storms. Thus, the severe threat and associated
rainfall after 18z seem a little more questionable. And while there
should be limited instability and plenty of shear at this time
range, the necessary forcing may be lacking to support any
organized convective activity.

With the system being fairly progressive, expect conditions to
improve steadily by Sunday night as the main upper level impulse
moves into the Great Lakes. This will leave behind a weak boundary
across the eastern half of the forecast area separating an
increasingly dry airmass across the Mid South and a more tropical
airmass across North Central Florida. As a secondary impulse
rounds the base of a large scale eastern CONUS trough on Monday
night into Tuesday, some of the guidance indicates the potential
for scattered showers and storms. As a result, will maintain
chance pops into Tuesday evening before finally clearing things
out by Wednesday morning.

Thereafter, most of the models are in good agreement that the Wed-
Thurs timeframe will be dry as high pressure builds across the
southeast. The only notable difference at this point is whether
the airmass will be near normal or much cooler than normal as
suggested by the 12z GFS. For now, have settled on a compromise
solution between the two with slightly below normal temperatures
across the region on Thanksgiving Day.

&&

.Aviation...
[Through 18Z Friday] VFR conditions will prevail through the next
24 hours.

&&

.Marine...
Light to moderate offshore flow will remain in place through this
evening. Thereafter, the gradient will sharply tighten between a
high pressure to the east and a strengthening low pressure system
to the west. This will result in a prolonged period of advisory
conditions starting on Friday night and continuing through Sunday.
Strong to severe storms are possible across the marine area late
Saturday night and continuing into Sunday.

&&

.Fire Weather...Low level moisture will gradually increase beginning
Friday with widespread rain overspreading the region Saturday
through Sunday.

&&

.Hydrology...A moderate to heavy rainfall event looks to be in the
offering this weekend starting late Saturday night continuing into
Sunday afternoon. Because the system will be progressive enough,
widespread flooding is not anticipated at this time. However,
synpotic forcing with this system is rather impressive,
particularly from 03z Sunday through 15z Sunday, thus there is the
potential in this timeframe for 2 to 4 inches of rain with
isolated heavier totals, primarily across our western areas. Flows
on area rivers are rather low and should be able to handle a
couple of inches of rain without reaching flood stage - though
widespread totals in excess of 3 or 4 inches may result in minor
flooding at a couple of river points in the first half of next
week, especially should this rainfall occur in the upper portions
of the Choctawhatchee and Chipola River basins.

In urbanized areas, minor flooding problems are possible,
particularly on Sunday morning across the Florida Panhandle and
into Southeast Alabama. Future forecasts may be able to better
define impacts as our hi-res output starts to depict this system
Friday afternoon.

&&

.Preliminary Point Temps/PoPs...

Tallahassee   33  68  46  70  64 /   0   0  10  10  90
Panama City   42  67  51  69  64 /   0   0  10  30  90
Dothan        38  67  44  66  59 /   0   0   0  10  90
Albany        35  67  43  66  59 /   0   0   0  10  90
Valdosta      34  66  46  69  61 /   0   0  10  10  90
Cross City    31  69  48  75  66 /   0   0  10  10  80
Apalachicola  40  66  52  68  66 /   0   0  10  30  90

&&

.TAE Watches/Warnings/Advisories...

FL...Red Flag Warning until 5 PM EST this afternoon for Coastal
     Wakulla-Inland Wakulla-Leon.

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

&&

$$

NEAR TERM...GODSEY
SHORT TERM...GODSEY
LONG TERM...GODSEY
AVIATION...GODSEY
MARINE...GODSEY
FIRE WEATHER...BARRY
HYDROLOGY...GODSEY




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