Area Forecast Discussion
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FXUS62 KTAE 221347
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
947 AM EDT Tue Apr 22 2014
.Near Term [Through Today]...
-- Changed Discussion --The local pattern this morning shows a mid/upper low amplitude
shortwave trough at the surface...a low on NY/Que border with slow
moving cold front across Nrn GA/AL. Satellite water vapor shows a
large area of showers and Tstms along and ahead of front moving Ewd.
In response..high pressure over the Ern Gulf shifts SWD allowing for
increasing lower cloud cover from NW-SE approaching NW CWA as
noted on Satellite VIZ.
During the rest of today...shortwave trough axis move east of CWFA
replaced by upstream ridging. This will push cold front to
S/Cntrl AL/GA by sundown with chances of precipitation increasing
into the late aftn. West winds ahead of front will increase to 10
to 15 mph. The deepest moisture and best lift with this system
will stay to our north. Locally...poor mid level lapse rates and
meager lower moisture translates to marginal instability and deep
layer shear so chance for strong to severe storms not high.
Still...H5 temps will be cool enough i.e. -14C combined with
surface temps in the low 80s and dew points approaching 60
degrees...enough ingredients for at least isold Tstms.
Since latest run has slowed down the front...onset of POPs have been
modestly delayed. PoPs by late afternoon show sharp 50-10% NW-SE
pop gradient. Kept mention of isolated to wdly sct TSTMS. QPF
amounts will generally be under one-quarter of an inch. Max Temps
will be in lower 80s inland areas and mid to upper 70s along the
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-- Changed Discussion --[Through 12Z Wednesday]...As morning fog continues to clear out
this morning, VFR cigs and vsbys will become prevailing. Around
18Z, thunderstorms will move in to the northern terminals (DHN,
ABY) from west to east, exiting the area by around 00Z. Around
09Z, MVFR visbys and IFR-LIFR cigs possible again at most sites.
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.Prev Discussion [235 AM EDT]...
-- Changed Discussion --.Short Term [Tonight Through Thursday]...
The 500 mb positive tilted trough (currently beginning to cross the
Southeast) will pass southeastward over our forecast area tonight,
but the accompanying weak cold front will stall across extreme North
FL and become oriented east to west. The forecast Q-vector and
omega fields are not that impressive, which may help explain why
neither the GFS or NAM MOS "likes" this system, and have PoPs of
only around 20%. However, our local Ensemble of Convection Allowing
Models (ECAM) forecasts good coverage of rain this evening across
South GA & AL, and its PoP is in the 50-80% range (but only 20%
around Tallahassee and Panama City). We blended the two sets of
differing guidance to come up with a PoP of around 50%. All of the
MOS and dynamical guidance forecast a strong weakening/drying trend
after midnight. Despite lack-luster synoptic scale forcing and
SBCAPE values of only around 1000 J/kg, a few thunderstorms are
possible- perhaps aided by fairly steep mid tropospheric lapse rates
of 6.5 deg/km. The lack of strong winds aloft, marginal CAPE, and
the rapid onset of nocturnal cooling all make severe thunderstorms
unlikely. Forecast updraft speeds are in the 10-15 m/s range, which
are usually not enough to support severe hail.
Despite the presence of a quasi-stationary front in extreme North FL
on Wednesday, the PoP will be 10% or less as the mid troposphere
warms and dries considerably. There may be a slight increase in deep
layer moisture on Thursday afternoon, and with the frontal system
still in the region, could lead to a shower or two. However, we`re
only carrying a 10% PoP for now. Temperatures will be near
climatology through the period, with lows in the 50s and highs in
the lower to mid 80s.
.Long Term [Thursday Night Through Monday]...
The large scale Srn stream pattern commences fairly progressive with
near zonal flow over Wrn states...weak trough over Cntrl states and
weak ridging over Ern states. On Friday...ridging moves offshore
leaving near zonal flow over SE region reflected in uni-directional
flow on model soundings. Flow shifts to weak WNW flow into Sat. On
Sun into Mon...upstream amplified ridging builds Ewd into Gulf
region. At surface...ridge becomes established over Nrn Gulf
thru Fri night. Then...a low well to the north of CWFA
brings a trailing weak front to our area on Sat where it likely
stalls by Sat eve providing a small chance of convection. Sheared
out front then lifts back Nwd on Sun. This will place local area in
warm sector allowing for a weak seabreeze to develop Sat-Mon.
Next cold front moves into SE on Mon yielding a modest increase on
precipitation across mainly NW half of CWA on Mon. With local area
in warm sector...temperatures are expected to be slightly above
climo with inland highs in the low to mid 80s and under the sea
breeze influence...somewhat cooler at the coast.
Despite the front approaching from the north later today, then
stalling across extreme North FL through Thursday, winds and seas on
the whole will remain quite low. The exception will be a moderate
increase in onshore winds and chop near the coast each afternoon
because of the daily sea breeze.
Red Flag conditions are not expected through the remainder of the
Most of our area rivers are above normal stage with many in flood
stage. The Choctawhatchee at Bruce is forecast to reach major flood
stage this morning, with several others in moderate flood stage.
Most area rivers will crest soon or have already crested. The
exception is the Suwannee River which will rise slowly for the
remainder of the week. QPF amounts through tonight are expected to
be a third of an inch or less (mainly in Southeast AL and Southwest
GA), and should not have a major impact on river levels.
The most up-to-date river forecast information can always be found
on our AHPS page (below).
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.Preliminary Point Temps/PoPs...
Tallahassee 82 60 83 58 84 / 20 20 0 0 10
Panama City 78 63 79 63 78 / 20 20 0 0 10
Dothan 81 59 83 58 84 / 40 50 0 0 10
Albany 83 58 83 56 84 / 40 50 0 0 10
Valdosta 82 59 84 59 85 / 20 20 10 10 10
Cross City 80 59 83 59 84 / 10 10 10 10 10
Apalachicola 75 61 76 63 77 / 10 10 0 0 10