Area Forecast Discussion
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979
FXUS62 KTAE 281850
AFDTAE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
250 PM EDT Sun Sep 28 2014

...Heavy Rainfall is still on the way...

.Near Term [Through Tonight]...

The 2 pm EDT regional surface analysis showed a rather ill-defined,
quasi-stationary front about 25 to 60 NM offshore the central Gulf
Coast, with progressively higher pressure to the northeast. Vapor
imagery and upper air data showed Precip water values exceeding 1.5
times normal values across much of our forecast area. Numerous
showers and thunderstorms have been developing over the Gulf Coastal
waters this morning & early afternoon, but so far the development of
rain inland has not been that impressive. However, all of the latest
NWP guidance is in agreement in increasing the Q-G forcing across
our region overnight, with the approach of a 500 mb trough
(currently over east TX). Thus we are confident in the eventual
development of rain across our entire forecast area.

The main forecast question is the amount of rain. Unfortunately the
NWP guidance offers quite a range of possibilities- from very little
QPF (with the heavy rain remaining just offshore) to areas exceeding
6 inches. The variety of solutions and lack of a single,
well-defined forcing mechanism makes it difficult to make a precise
rain amount forecast, but at the overall synoptic environment does
point to the potential for heavy rain, especially the abnormally
high moisture values. We think that portions of our forecast area
will get 1 to 2 inches of rain between now and 8 am EDT Monday, but
a few spots could get 6 inches. If these heavier amounts occur in a
city (or in any low- lying, poor drainage area), flash flooding
could occur.

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

With plenty of deep layer tropical moisture already in place across
the CWA and points westward (widespread PWATs between 2" and 2.3"),
and the forcing for lift coming from a slow moving shortwave now
over western LA, a fairly widespread heavy rainfall event is still
expected across much of the region through Monday. Storm total
rainfall amounts are expected to average between 1.5" to 2.5" across
much of SE AL and SW and SC GA, with 2.5" to 4" amounts likely
across much of the Florida Big Bend and Panhandle before all is said
and done. The heaviest amounts are still likely closest to the
coast, with parts of Bay, Walton, Gulf, Franklin, and Dixie counties
in FL possibly totaling over 4", with isolated 5-7" amounts not out
of the question. Also, given the poor organization and slow movement
of this low pressure system, there is still a reasonable amount of
uncertainty to warrant a continuation of the Flash Flood Watch for
the entire CWA through the day on Monday. PoPs on Monday will range
from 60 to 80% through the day, with this rainfall event gradually
winding down and coming to an end on Monday Night and Tuesday. With
plenty of clouds and rain, High temps tomorrow will struggle to climb
into the upper 70s to the middle 80s, with more widespread middle to
perhaps upper 80s on Tuesday as more insolation is expected. Low
temps both Monday and Tuesday nights should range from the lower to
middle 60s N, to the upper 60s to around 70 to the S.

.Long Term [Wednesday Through Sunday]...

After a very wet pattern over much of the near and short term
periods, we expect to have a brief break in the unsettled weather
later on Tuesday and through Wednesday, as both Sfc and upper level
ridging build in for a short time. Thereafter, showers and
thunderstorms are expected to return to the fcst in earnest on
Thursday and Friday, as the strongest cold front of the season thus
far approaches from the NW. This cold front is expected to bring a
real taste of fall to the region by Saturday and Sunday, with low
temps possibly reaching the lower to middle 50s over the interior on
Sunday morning, with much drier air also building in under the NW
flow. High temps will still be very close to climo levels, however,
generally in the lower to middle 80s on Sat and Sun. Before the
frontal passage, above normal temperatures are expected to persist,
with the warm and humid air struggling to budge.

&&

.Aviation...

[through 18Z Monday] Mainly MVFR cigs will be the rule through this
evening, along with periods of rain. The warm rain processes will
coincide with IFR Vis at times. The highest PoP will be at KECP and
KTLH early, then gradually spread to KVLD, KDHN, and KABY later this
afternoon and evening. Periods of rain are likely all night and into
Monday morning. Isolated TSRA are expected as well. Cigs will
gradually descend to IFR levels overnight and into Monday morning.

&&

.Marine...

Once again, winds and seas are running a little bit higher out of
the east to southeast than the models have been projecting, due to
the combination of a tighter pressure pattern and the numerous
showers and thunderstorms which keep developing over the marine
area. However, these winds and seas should stay below cautionary
levels through the period, while gradually decreasing. By Tuesday
night and Wednesday, winds will diminish to between 5 and 10 knots
out of the northeast, with seas dropping to around 1 foot.

&&

.Fire Weather...

Hazardous fire weather conditions are not expected over the next few
days.

&&

.Hydrology...

As mentioned above, storm total rainfall amounts are expected to
range from 1.5" well to the north in our HSA, to 4" or more well to
the south. Depending on exactly where the highest rainfall totals
are observed, will determine the potential flooding impacts on our
area rivers and streams. At the present time, the rivers most likely
to be impacted with significant rises would be the Choctawhatchee,
Apalachicola, and the Suwannee, though it would likely take more
rainfall than we are currently forecasting to bring them into flood
stage.

.Preliminary Point Temps/PoPs...

Tallahassee   71  86  69  87  67 /  80  70  50  30  10
Panama City   73  85  70  85  72 /  80  80  40  20  10
Dothan        69  83  64  87  64 /  80  80  30  10  10
Albany        70  81  65  86  64 /  80  80  30  10  10
Valdosta      71  83  67  85  63 /  80  80  50  30  10
Cross City    71  85  70  86  66 /  80  70  60  40  10
Apalachicola  74  85  72  83  72 /  80  70  50  30  10

&&

.TAE Watches/Warnings/Advisories...

FL...Flash Flood Watch through Monday evening for Calhoun-Central
     Walton-Coastal Bay-Coastal Dixie-Coastal Franklin-Coastal
     Gulf-Coastal Jefferson-Coastal Taylor-Coastal Wakulla-
     Gadsden-Holmes-Inland Bay-Inland Dixie-Inland Franklin-
     Inland Gulf-Inland Jefferson-Inland Taylor-Inland Wakulla-
     Inland Walton-Jackson-Lafayette-Leon-Liberty-Madison-South
     Walton-Washington.

     High Rip Current Risk until 6 PM EDT this evening for Coastal
     Franklin.

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

AL...Flash Flood Watch through Monday evening for Coffee-Dale-Geneva-
     Henry-Houston.

GM...None.

&&

$$

NEAR TERM...FOURNIER
SHORT TERM...GOULD
LONG TERM...GOULD
AVIATION...FOURNIER
MARINE...GOULD
FIRE WEATHER...FOURNIER
HYDROLOGY...GOULD/FOURNIER






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