Area Forecast Discussion
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326
FXUS62 KTAE 221044
AFDTAE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
640 AM EDT Tue Jul 22 2014

.Near Term [Through Tonight]...

Updated at 640 am EDT- The 11 pm EDT regional surface analysis
showed a decaying, wavy, quasi-stationary, front from SC, through
central GA, extending southwestward to a broad, 1015 mb low centered
over southern MS. There was an east-west trough along I-10 in the FL
Panhandle. Vapor imagery and upper air data showed a cutoff low
centered over southwest GA, with a well-defined dry slot wrapping
around the west and southwest flank of the low, over the FL
Panhandle and adjacent coastal waters.

The GFS and ECMWF forecast the upper low to translate slowly
westward. Although they differ somewhat in magnitude, the consensus
of MOS and the Convection Allowing Models (ECAM) PoPs generally
range from 30 to 50% across our forecast area today, highest over
our eastern zones. This is slightly lower than what we had a few
hours ago, as the latest NWP guidance may be picking up on the
impressive drying observed on satellite imagery over the western
half of our forecast area. The most concentrated area of deep moist
convection will initially be across Apalachee Bay and the FL Big
Bend/North FL this morning. This activity will gradually move inland
and diminish later this morning, but scattered storms will develop
across GA and AL this afternoon in association with the forcing from
the upper low and any mesoscale boundary interactions that occur.
Given the very weak wind field aloft and lackluster forecast SBCAPE
values (1500 J/kg or less), we`re expecting a less than 5% chance of
severe storms (within 25 miles of a point) today. We expect high
temperatures to be a little warmer today than in recent days- around
90.


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

A mid-upper level low will continue to retrograde westward along
the Gulf coast and eventually get sheared out near coastal
Louisiana or Texas by Thursday. For Wednesday, this will allow for
a ridge to build into the area with negative vorticity advection
in those same layers. Computer models are in good agreement in
showing suppressed convective activity on Wednesday despite PWATs
very close to seasonal normals (around 1.9"). While this may be
the case, we think that the approx 20% PoPs the models are
advertising for the afternoon hours are too low without any
substantial drying - either at the surface or aloft. By Thursday,
another trough begins to dig into the region from the northwest
and could provide some additional large scale forcing for storms.
Therefore, we indicated scattered thunderstorms both afternoons
with PoPs around 30-40% in most areas. Temperatures should be
warmer than in recent days, with highs in the mid 90s likely.


.Long Term [Friday Through Tuesday]...

The large scale pattern commences rather amplified with ridging
over west, troughing over east and ridge over extreme Wrn Atlc.
At surface, ridge from Wrn Atlc to over local region with cold
front draped over mid-south. During the rest of the period, Wrn
ridge shifts Ewd with downstream trough pivoting and deepening Ewd
over local region on Fri before lifting Newd and flattening Sat
into Sun. Front inches swd shunting Gulf ridge further Swd
allowing for a return to a more WLY flow and normal summer time
sea breeze dominated regime. Will go with generally 30-40% aftn/eve
POPs thru the period. Expect highs generally in the low to mid
90s, lows low to mid 70s.

&&

.Aviation...

[Through 12Z Wednesday] Areas of MVFR cigs remain possible this
morning. Otherwise, scattered TSRA will develop today, with the
highest chances (40-50%) around KTLH and KVLD later this morning and
early afternoon, then around KABY later this afternoon. Gusty winds
and brief periods of poor VIS/CIGS are expected with the stronger
storms, but we were not confident enough to explicitly forecast
these conditions at any terminals on this 12 UTC TAF package.

&&

.Marine...

Winds and seas should be relatively calm during the period - winds
generally 10 knots or less and seas generally 2 feet or less.

&&

.Fire Weather...

Red flag conditions are not expected this week.

&&

.Hydrology...

The Shoal River at Mossy Head briefly approached flood stage early
yesterday morning, but the river levels are now falling. There
will likely be some heavy rain rates today, and the storm motion
will be unusually slow (around 5 kt). This would suggest at least
some potential for flooding. However, there appears to be one
negative factor that will keep the risk of flooding rather low-
the influx of dry air aloft from the south and west. This should
help dampen deep moist convection somewhat, preventing updrafts
from persisting over any one location for too long. We think the
probability of exceeding local flash flood guidance today is about
5% (within 25mi of a point), which is not high enough for a watch.

&&

.Preliminary Point Temps/PoPs...

Tallahassee   90  72  95  73  95 /  50  30  50  20  50
Panama City   87  75  90  76  90 /  30  20  30  20  30
Dothan        89  72  93  73  93 /  40  20  40  20  40
Albany        90  72  94  73  94 /  40  40  30  20  30
Valdosta      90  70  96  72  96 /  40  40  40  20  40
Cross City    90  71  94  73  92 /  60  30  40  20  40
Apalachicola  87  74  88  76  88 /  50  20  30  20  30

&&

.TAE Watches/Warnings/Advisories...

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

&&

$$

NEAR TERM...FOURNIER
SHORT TERM...LAMERS
LONG TERM...BLOCK
AVIATION...FOURNIER
MARINE...LAMERS
FIRE WEATHER...FOURNIER
HYDROLOGY...LAMERS








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