Area Forecast Discussion
Issued by NWS
FXUS62 KTAE 130907
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
507 AM EDT Thu Jun 13 2013
...THERE IS A POTENTIAL FOR SEVERE THUNDERSTORMS THIS AFTERNOON AND
EVENING WITH THE PRIMARY THREAT BEING DAMAGING WINDS...
.NEAR TERM [Today and Tonight]...
Very interesting forecast across the region over the next 24 hours,
as the very hot conditions which were observed across the CWA on
Wednesday will continue over the region today. High temps are once
again expected to reach the upper 90s across much of the interior
this afternoon, with lower to middle 90s as we gradually approach
the coast. However, the upper level ridging (and low level NW flow)
which helped to suppress and limit the afternoon Sea Breeze
convection to a general area confined near the coast, will be
retrograding westward today, which will allow a shortwave trof and
weak Cold Frontal boundary to approach from the NW tonight. While
PoPs from the Sea Breeze convection are only expected to be slightly
higher across the region this afternoon (ranging from 20% to the NW
to 40% to the SE), it is the potential MCS development out ahead of
the Cold Front which has us quite a bit more concerned for tonight.
In fact, the Storm Prediction Center (SPC) has placed all of our AL
and GA zones in a Slight Risk for Severe Thunderstorms, with the
main threat being damaging wind gusts. The main question for our
region will be the timing of this convection, which we currently
believe will be mainly in the 00 to 06 UTC window this evening over
our northern zones (with 40% PoPs which may need later adjustment),
with the earlier the arrival likely equating to greater potential
for severe storms. This potential will at least be somewhat tied
to evening temperatures, which could still be around 90 degrees, so
when combined with SFC dewpoints in the lower 70s, will still
support a very unstable environment for the convection to develop
and propagate southward. Therefore, all interests in our CWA should
keep abreast of the latest forecasts, briefing information, and
updates from both our local office and the Storm Prediction Center
should a Severe Thunderstorm Watch become necessary later today or
tonight. In any event, most of of the Hi-Res models are indicating a
definitive weakening trend in the convection during the overnight
hours, so the threat should be diminishing as the night goes on.
.SHORT TERM [Friday Through Saturday Night]...
The short term period begins with an upper level pattern much like
the one our area has been under for the past couple of days. The
only difference being now an upper level trough is moving off the
eastern seaboard, and deep layer ridging is advancing eastward. A
weak surface cold front, associated with the upper level trough,
is expected to be just north of the Florida border by 12Z Friday.
Therefore, expect an enhanced PoP ahead of the cold front as it
slowly advances southward. The Storm Prediction Center has a 5%
probability of severe weather outlined for ahead of the surface
cold front. If severe weather should occur, it will likely be high
winds. Looking at the equivalent potential temperature difference
between the surface and the 500-700mb layer, values are in the
lower 30s, which would indicate a marginal potential for damaging
winds being transported to the surface. The mid-level temperatures
are too warm to support the possibility of severe hail making it
down the surface.
By early Saturday morning, the cold front should stall out south of
our CWA. Therefore expect drier conditions throughout the day on
Saturday with no POPs expected. PWATs throughout the area will be
less than 1.3, which is abnormally low for this time of year. The
surface high pressure will quickly push eastward through the day
on Saturday with winds transitioning from northerly to easterly.
By the end of the near term period winds will be southerly,
returning our area to our normal summertime weather pattern.
.LONG TERM [Sunday through Wednesday]...
After the potential system passes Thursday night, high pressure
aloft and at the surface will build eastward and be the main
synoptic scale influence on the forecast area`s weather through
Tuesday. On Tuesday, another shortwave will propagate through the
upper level ridge and set up a pattern similar to Thursday night
(see short term). Highest PoPs in the forecast period are Tuesday
and Wednesday. Expecting highs in the 90s and lows in the low 70s
through the long term period.
[Through 12 UTC Friday] Although generally VFR conditions are once
again expected to prevail for the majority of the overnight period,
there are once again enough discrepancies both within the Hi-Res
guidance (the HRRR and the NARRE), and between this and the
numerical guidance to make the fcst a bit tricky. It appears that
the HRRR is unusually a bit pessimistic (but does appear to have the
likely favored areas for possible restrictions), so used a blend
with persistence. Once again, believe DHN and ECP will need to be
monitored the most closely should IFR of LIFR Vis/Cigs develop
towards morning. During the afternoon and next evening hours, rain
chances will be greater across the area than the previous 2 days, as
showers and storms may form both along the Sea Breeze Front
initially, and on the southward moving Cold Frontal boundary
thereafter. Used convective Prob30 groups to account for this, with
the timing from south to north, and did include gusty winds as some
of the thunderstorms could be strong to severe.
With the approach of a surface cold front, the pressure gradient
will tighten allowing for increased winds. Beginning this
afternoon, small crafts should exercise caution with winds
expected to be 15-20 knots through early Friday morning. A chance
for thunderstorms is expected through the day on Friday.
Red Flag or near Red Flag conditions are not anticipated across the
Tri-State area for the next several days.
The Ochlockonee River at Thomasville is in action stage and may
rise slightly with rain tomorrow night, but it is not expected to
reach minor flood stage. MMEFS shows no sites are forecast to
reach flood stage in the near future. Although there is potential
for some severe thunderstorms Thursday night, WPC QPF for our area
is 0.25" or less and is not expected to cause significant rises on
.PRELIMINARY POINT TEMPS/POPS...
Tallahassee 96 75 94 71 93 / 30 20 30 10 10
Panama City 91 78 88 77 87 / 30 10 30 20 10
Dothan 99 74 94 70 95 / 20 40 20 0 10
Albany 99 74 93 70 93 / 20 40 10 0 10
Valdosta 97 74 95 70 95 / 40 30 30 10 10
Cross City 92 73 91 72 92 / 30 20 30 20 10
Apalachicola 89 77 87 76 86 / 20 10 30 20 10