Area Forecast Discussion
Issued by NWS
FXUS62 KTAE 220616
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
216 AM EDT Tue Jul 22 2014
.Near Term [Through Tonight]...
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, providing weak Q-G forcing across GA & AL today. It
also appears that there will be slightly more deep layer moisture
in this region as well. Although they differ somewhat in
magnitude, the consensus of MOS and the Convection Allowing Models
(ECAM) PoPs generally range from 40 to 60% across our forecast
area today. 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.
[Through 06Z Wednesday] The latest HRRR runs and GFS MOS suggest
a good chance of low-end MVFR/IFR CIGS through mid morning at
every site but KTLH. Conditions will improve to VFR by late
morning, outside of scattered TSRA. Initially the TSRA will be
concentrated near KTLH, but will spread to KVLD, KABY, and KDHN by
afternoon. The probability of TSRA at each terminal is 40-50%
today, except 30% at KECP. Of course gusty winds and brief period
of poor VIS/CIGS are expected with the stronger storms, but we
were not yet confident enough to explicitly forecast these
conditions at any site on the 06 UTC TAF package.
Winds and seas should be relatively calm during the period - winds
generally 10 knots or less and seas generally 2 feet or less.
Red flag conditions are not expected this week.
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