Area Forecast Discussion
Issued by NWS
FXUS62 KTAE 110752
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
352 AM EDT Sat May 11 2013
.NEAR TERM [Today]...
The forecast today remains somewhat uncertain as much will depend on
the mesoscale evolution over the next 6-12 hours. The surface
pattern is quite muddled due to upstream MCS activity from Texas to
coastal Louisiana in the past day or two. Objective analysis places
a surface trough and convergence zone along the Louisiana coast,
extending east into the coastal waters adjacent to the FL Panhandle
coastline. Thunderstorms have developed early this morning just
north of the richer surface thetae (likely elevated slightly), and
ahead of an advancing mid-level MCV over coastal SW Louisiana. The
vast majority of both global and convection-allowing models (CAM)
had indicated a focused area of QPF near coastal Louisiana in the
12-18 UTC time frame, which means that things appear to be "ahead of
schedule" by a few hours. The model that seems to most closely
resemble reality right now (at 07 UTC) is the HRRR. Therefore, the
progression of PoPs and temperature trends closely follow the HRRR
and RAP models. For the forecast, this means we began increasing
rain chances in the western part of our area around 16-18 UTC
(around the noon hour), with an eastward progression from there
during the afternoon hours. High temperatures were kept highest in
the east, where cloud cover and rain will be last to arrive.
With respect to the intensity of thunderstorms, there is also a bit
of uncertainty. The initial SPC SWODY1 places us in 5% probabilities
of severe hail and wind. This seems reasonable given a lack of
clarity in the mesoscale details. The best chances of seeing a
strong or severe storm look to be where any sort of heating is able
to occur before cloud cover increases. In most of the available
models, areas that are able to get heating in the morning see about
1000-1500 j/kg of CAPE in the afternoon, with around 25-30 knots of
0-6km shear. It is in these favorable intersections of instability
and shear where a severe storm or two would be most likely. Impacts
would probably be rather isolated though. Assuming dewpoints in at
least the mid-60s, surface based (and the strongest) storms would be
most likely in areas that can get into the 80s temperature-wise.
.SHORT TERM [Tonight through Monday]...
The 00 UTC NWP guidance continues to forecast an unusually deep
longwave trough over the eastern CONUS Sunday and Monday. The PoP
will decrease from northwest to southeast Sunday as dry air
advection develops. The highest PoP, 30-40%, will be from
Tallahassee southward and eastward tonight and Sunday, with the PoP
decreasing below 10% Sunday evening. The core of the cooler and
drier airmass won`t reach our forecast area until Monday. Highs on
Sunday will be in the lower 80s, but only in the 70s (below average)
Monday. Lows on Monday morning will be in the 50s (also below
average). The low humidity and relatively breezy conditions on
Monday will make it feel quite pleasant for mid May, when it usually
begins to get warm and humid.
.LONG TERM [Monday Night through Friday]...
Deep layer ridging will build into the region for the middle of the
week followed by a low amplitude trough late Thursday into
Friday. There will be a slight to low end chance of rain on
Friday, otherwise the extended period will be dry. The week will
begin with below normal temperatures and gradually moderate to
seasonal levels by Thursday. The coldest temperatures will be
Tuesday morning when upper 40s to around 50 degrees are forecast.
.AVIATION [Through 06 UTC Sunday]...
As some mid-high level cloud cover clears out of our area for the
last half of the overnight period (06-12 UTC), we are expecting some
patchy fog or low stratus to develop, with periodic reductions to
MVFR or IFR. Conditions should improve around 13-14 UTC. After that,
the outlook is VFR, although there may be some thunderstorms today
moving into the area from the west. Timing looks to be beginning
around 16-19 UTC at ECP and DHN, to as late as 21-00 UTC at VLD. In
any of the thunderstorms, brief reductions in the flight categories
would be expected, as well as the possibility of some gusty winds.
However, confidence in timing and location of storms is not high
enough to include in prevailing or TEMPO groups at this time.
Aside from the increased rain chances, weekend boaters will be
treated to low winds and seas (outside of scattered thunderstorms).
This will change Sunday night as the rather strong area of high
pressure builds across the Southeast behind a cold front, causing
winds to increase to 15 to 20 KT. These offshore winds may remain at
exercise caution levels through Tuesday morning.
Wetting rains are expected over a good portion of the area today.
Drier air will arrive behind a cold front on Sunday Night with very
low RH for May expected on Monday. Despite the minimum RH around
25%, other fuel-dependent red flag criteria may not be met. Thus,
while red flag conditions seem somewhat uncertain, there is high
confidence that Monday will be a breezy, dry day with high
The 00 UTC WPC 5-day rainfall accumulation forecast continues to
show our between one half and one inch over our forecast area,
mainly this weekend, and with the highest totals west of
Tallahassee. None of the experimental hydrologic ensembles forecast
minor flooding for our river forecast points over the next several
days. The maximum of maximum 6-hour QPF amounts from the various
Convection Allowing Models (CAM), a worst case scenario, show
isolated narrow bands of 3-4 inches. Neither the area coverage or
magnitude of these values would indicate enough of a threat for a
flash flood watch for today`s rain.
.PRELIMINARY POINT TEMPS/POPS...
Tallahassee 83 66 82 53 80 / 70 40 30 10 0
Panama City 77 67 81 57 78 / 70 40 20 10 0
Dothan 81 63 79 50 78 / 70 40 10 0 0
Albany 85 64 81 50 76 / 60 40 10 0 0
Valdosta 86 64 81 52 77 / 70 40 30 10 0
Cross City 84 66 82 57 80 / 40 30 40 10 0
Apalachicola 79 67 79 59 76 / 60 30 30 10 0