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Area Forecast Discussion

017
FXUS62 KTAE 290117
AFDTAE

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

...Heavy Rainfall is still possible through Monday...

.Update...

Through 01z, most of the rainfall has been confined to the Florida
zones and adjacent coastal waters. The heaviest rains over land have
been along the coast of Gulf and Franklin counties and over portions
of the southeast Big Bend. These areas based on radar estimates and
reporting gauges have received between 1 and 3 inches of rain. Local
radars currently show scattered convection generally along and south
of a Panama City to Valdosta line. We still believe that as the
upper level trough and eventual develop of a surface low along the
central Gulf coast moves east there is still the potential for heavy
rainfall across the Tri-state region. For this reason, we will keep
the Flash Flood Watch in place. PoPs have been trimmed back slightly
for the overnight period but are still in the likely to categorical
range.

.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 00Z Tuesday] Trimmed back mention of TSTMS for most periods
of the TAF cycle. Otherwise, fairly pessimistic forecast with
MVFR/IFR cigs/vsbys along with periods of rain throughout. Some of
the rain may be heavy at times possibly lowering vsbys to LIFR
levels, especially at ECP and TLH.

&&

.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.

&&

$$

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




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