Area Forecast Discussion
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248
FXUS62 KTAE 142111
AFDTAE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
511 PM EDT Mon Apr 14 2014

.Near Term [Through Tonight]...
Subjective analysis at 18Z placed an outflow boundary from Gulfport
MS, to Mobile AL, to Troy AL, to Columbus GA - or very near the
northwest corner of our forecast area (Coffee Co AL). The cold pool
behind the outflow boundary was characterized by temperatures in the
60s with cloudy skies and light to moderate rain. Meanwhile, a
subtle coastal front extended from near Dauphin Island, Alabama to
Apalachicola. These two boundaries could play a role in focusing
convection later tonight. Models are in good agreement in showing
fairly widespread thunderstorm development in the next 6 hours (by
03Z) ahead of a strong, advancing cold front to our west. This
activity then would move across the area from west to east, mainly
between 06Z and 16Z. The environment should support heavy rainfall
in thunderstorms, with PWATs expected to be around 1.8-1.9 inches
(approximately 2-3 standard deviations above normal, or in the 99th
percentile for TLH April climatology). PoPs were increased to
90-100% and heavy rainfall wording was inserted.

Convection-allowing models (CAM) are consistently showing a band of
heavy rainfall along the Gulf coast tonight and Tuesday morning from
southeast Louisiana into our local area (especially the Florida
Panhandle). Although they vary slightly in the placement of this
relatively narrow band, the rainfall totals are fairly consistent:
an inch or so outside of the heavier band, 2-4" within the band and
isolated totals possibly double that in very localized areas.
Additionally, an ingredients-based assessment supports some brief
(2-3hr time scales) training of convective elements. The SEwd
drifting outflow boundary may combine with the Nwd lifting coastal
front to create a WSW-ENE oriented thetaE gradient that could aid in
focusing thunderstorms. A strengthening southwesterly LLJ should
increase low-level moisture flux and forcing along the boundary as
well as in the broader WAA regime. These factors, combined with the
high precipitable water values, all suggest a heavy rainfall and
possibly flash flooding threat. For that reason, we have issued a
Flash Flood Watch for most of the area except the Apalachee Bay and
eastern Florida Big Bend counties where models are consistently
showing less QPF. Regarding the severe weather threat, isolated
severe storms can`t be ruled out. The main threat would be damaging
winds. We expect the highest chances of severe storms would be along
and south of I-10 where greater instability should exist along and
south of the coastal front.

&&

.Short Term [Tuesday Through Wednesday night]...
The main band of convection (with some strong to severe storms and
locally heavy rainfall) with the approaching cold front will be
ongoing across much of the CWA on Tuesday morning, before a stronger
Sfc low develops and ejects to our NE and begins to rapidly sweep
the cold front through the CWA during the afternoon. Given the
expected fast movement of the pre-frontal squall line, the overall
threat for flash flooding will be decreasing from west to east
across the CWA, with the SE FL Big Bend anticipated to receive storm
total rainfall on the order of 1 to 1.5" when all is said and done.
While this is not expected to cause any areal or flash flooding in
this region, riverine flooding along the Aucilla and Suwannee Rivers
will remain a distinct possibility. After the cold front moves
through, much colder and drier air will rush in from the northwest
on Tuesday night. Despite plenty of numerical guidance which is
indicating low temps possibly reaching the freezing mark or below
across portions of the western interior, believe this is a very
unlikely scenario given the saturated ground and elevated winds
overnight. Nevertheless, even the raw model data is quite cold for
this time of year, so used a blend of the raw GFS and SREF, which
still results in enough cold air advection to produce a fairly large
area of low temps in the mid to upper 30s, which is about 15 to 20
degrees below climatology! A sunny but cool and dry day is expected
for Wednesday, with highs only reaching the mid to upper 60s in most
areas, with a few lower 70s well to the SE. Wednesday night will
still feature below normal temps with lows in the lower to mid 40s
to the north and upper 40s to around 50 to the south.


.Long Term [Thursday Through Monday]...
With the first low pressure system long gone by the beginning of the
extended period, we should at least experience a 2 day break in the
unsettled weather on Wed. and Thu. with an initial shot of
unseasonably cold air moderating back towards climo levels. By the
end of the week and through next weekend, however, the fcst will
once again become quite difficult as the conditions are leaning
heavily towards yet another very unsettled period. While the details
on timing, potential rainfall totals, and the possibility of any
severe weather have been very inconsistent from run to run in both
the GFS and ECMWF, the chances of another significant rainfall event
during this time frame are clearly increasing. This is definitely
not welcomed news for our area rivers and streams, many of which
remain elevated from previous rainfall events, and will be primed
yet again by the initial rainfall event early in this week.
Furthermore, until a more significant change in the synoptic pattern
becomes evident across the CONUS, these anomalous digging shortwaves
and potential heavy rainfall producers will continue to threaten the
SE U.S.

&&

.Aviation...
[through 18z Tuesday] Generally VFR conditions this afternoon should
gradually give way to IFR CIGS overnight, with stratus likely
spreading inland from the coast. Therefore, ECP and TLH should be
affected first, followed by the inland terminals. Thunderstorms will
advance across the area from west to east, and should affect all of
the terminals at some point between 05Z in the west and 17Z in the
east. Some of the storms could produce gusty winds and heavy
rainfall with brief VIS reductions to LIFR.

&&

.Marine...
Onshore winds and seas will gradually increase to cautionary levels
tonight as series of developing waves of low pressure to our west
will move northeastward from central LA to a position well to the
north of the marine area by Tuesday morning. The final and strongest
surface low in this series will then push a strong cold front from
west to east across the waters on Tuesday, resulting in quickly
developing Small Craft Advisory conditions as winds shift from
southwest to northwest. Then, strong northerly winds will linger
through Wednesday morning before the Advisory level conditions
slacken as the winds become northeasterly in the afternoon.
However, this break in the adverse marine conditions is expected to
be short lived, as moderate to strong easterly winds are expected to
quickly return and then last throughout the remainder of the week.

&&

.Fire Weather...
Widespread wetting rain is expected later tonight and into Tuesday
morning. This should limit fire weather concerns over the next 24
hours and increase fuel moisture. A drier air mass is expected on
Wednesday, but fuel moisture levels should continue to be high.

&&

.Hydrology...
Rainfall forecasts for tonight and early Tuesday continue to point
toward increased confidence in a localized convective band of heavy
rain setting up from the FL panhandle up toward southwest GA. In the
area where any band sets up, rainfall amounts could easily range
from 2 to 4 inches with higher amounts likely. Convectively induced
heavy rainfall in any given area could result in flash flooding,
especially over urban locations, with the general area of concern
north and west of a line from Apalachicola to Tallahassee to
Valdosta. River basins more likely to be affected include parts of
the lower Choctawhatchee, Chipola, Apalachicola, and Ochlockonee.
Additional rainfall tonight and Tuesday will slow the falling trend
on area rivers and lead to rises on some, particularly in smaller
basins. This will result in longer lived flooding this week along
some area rivers, but given the uncertainty on where localized heavy
bands of rain set up, it`s difficult to say which rivers may see the
most notable rises.

For real-time detailed river stage monitoring refer to this page:
http:/water.weather.gov/ahps2/index.php?wfo=tae

&&

.Preliminary Point Temps/PoPs...

Tallahassee   65  71  39  70  47 /  90  90  10   0  10
Panama City   64  68  43  67  52 / 100  70   0   0  10
Dothan        59  64  36  66  43 / 100  80   0   0  10
Albany        64  65  36  66  43 / 100  90   0   0  10
Valdosta      65  68  40  69  45 /  40  90  10   0  10
Cross City    66  73  43  72  48 /  10  90  10   0  10
Apalachicola  66  69  45  66  55 /  60  80  10   0  10

&&

.TAE Watches/Warnings/Advisories...

FL...Flash Flood Watch from 10 PM EDT /9 PM CDT/ this evening through
     Tuesday morning for Calhoun-Central Walton-Coastal Bay-
     Coastal Gulf-Gadsden-Holmes-Inland Bay-Inland Gulf-Inland
     Walton-Jackson-Leon-Liberty-South Walton-Washington.

     High Rip Current Risk until 6 PM CDT this evening for Coastal
     Bay-South Walton.

GA...Flash Flood Watch from 10 PM EDT this evening through Tuesday
     morning 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 from 9 PM CDT this evening through Tuesday
     morning for Coffee-Dale-Geneva-Henry-Houston.

GM...Small Craft Advisory from 8 AM Tuesday to 2 PM EDT Wednesday for
     Apalachee Bay-Coastal waters From Ochlockonee River to
     Apalachicola FL out to 20 NM-Coastal waters from Suwannee
     River to Keaton Beach FL out 20 NM-Coastal waters from
     Apalachicola to Destin FL out 20 NM-Waters from Suwannee
     River to Apalachicola FL from 20 to 60 NM-Waters from
     Apalachicola to Destin FL from 20 to 60 NM.


&&

$$

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








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