Area Forecast Discussion
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FXUS62 KTAE 041459
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
959 AM EST Tue Mar 4 2014
.Near Term [Through Today]...
-- Changed Discussion --Low level isentropic ascent, coupled with an upper level shortwave
produced a large area of convection across the western Gulf
overnight/early this morning. The mid-level diabatic heating max
will move east rather quickly today in the fast westerly flow
regime. The 00z ECMWF and recent RAP runs have initialized the
spatial extent of the convection more accurately and will thus
weight the forecast for this afternoon more heavily on these
pieces of guidance.
This mornings surface analysis showed yesterday`s cold front
draped across south central Florida, and on through the central
Gulf. Cool high pressure across the Mid-Atlantic forced an area
of low pressure to weaken and drift south into a more favorable
environment. This morning, a remnant trough runs south along the
lee side of the Appalachians, into Apalachee Bay. A sharp
inversion around 1500ft marks the delineation between the stable
saturated low layers and a large area of dry air aloft. Low clouds
remain trapped in this stable low layer. Expect the surface trough
to continue to gradually weaken and drift west with the very
stable cool dome spreading southwest behind it. Low clouds will
likely linger for most of the day, though some scattering is
expected along and ahead of the trough. For now, will advertise
the best chance for scattering along and west of a line from
Alligator Point, up through the southeast Alabama/southwest
Georgia state line. As one would imagine, the thick low cloud
cover will greatly limit afternoon heating. Expect highs to not
reach 50 degrees across our northeast Georgia counties, with upper
50s expected in the aforementioned region where scattering is
expected to take place. The exact position of the scattering line
is highly uncertain, so the takeaway here is that if clouds
scatter away where you are, highs should climb into the upper 50s.
Otherwise, expect temperatures to remain much cooler.
Not expecting much in the way of rain today, and any rain that
does fall will be over our extreme western counties late in the
day as the aforementioned mid-level PV anomaly links up with the
low-level surface trough. In this region expect a mix of weak low
level WAA, to combine with weak low/mid layer isentropic ascent,
but more significantly, strong mid-level diffluent flow in the
entrance region of an intensifying jet. Rain chances will only
increase through Wednesday as discussed further, below.
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-- Changed Discussion --[Through 12Z Wednesday]...
Low-end MVFR/IFR ceilings will persist all day at KABY, KVLD, and
possibly KTLH and KDHN. Expect scattering to VFR at KECP later
this afternoon. Rain spreading in from the west overnight will
reinforce the low ceilings area wide once again tonight.
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.Prev Discussion [609 AM EST]...
-- Changed Discussion --.Short Term [Tonight Through Thursday]...
Fast split flow will continue across the CONUS. No sooner will one
short wave trough move through our region (late tonight-Wednesday)
when another will already be approaching over the Southern Plains.
We`re forecasting an 80% PoP overnight for our entire forecast area,
though QPF amounts are generally less than a third of an inch. Even
though this short wave will be dampening as it moves past our
region, high PoP will continue across much of the region on
Wednesday due to the proximity to a frontal system (the cold front
that passed through Monday) and the rapid approach of the next short
wave trough. High PoPs will continue through Thursday morning, then
end quickly from west to east as a well-defined mid tropospheric dry
slot develops over the forecast area during the day on Thursday.
Our QPF total from tonight through Thursday ranges from 0.75 to
1.50 inches. Although both of the upper troughs will be rather
energetic (with decent height falls and strong winds aloft), both
the GFS and ECMWF continue to place our forecast area north of the
surface frontal system. This means that while there could be
occasional thunderstorms, the boundary layer will be stable and
these storms will be elevated. Thus we don`t expect any damaging
winds or tornadoes. The one possible exception could be in North
FL (around the Cross City area), where the GFS and ECMWF forecast
at least some SBCAPE. A surface low track slightly farther to the
north would increase this threat. Conversely, a more southern
track would eliminate the threat.
With all of the clouds/precipitation and a "wedge" of cool air in
place over GA and AL, high temperatures will be rather chilly
Wednesday- with highs in the mid 50s (except mid 60s around Cross
City). The wedge will get eroded some on Thursday, with highs in
the mid to upper 50s in GA and AL, and in the mid to upper 60s in
FL. Lows will be in the lower to mid 40s across most of the
forecast area tonight (upper 40s around Cross City), and mid to
upper 40s Thursday night (except mid 50s Cross City).
.Long Term [Thursday Night Through Tuesday]...
On Thursday night..as trough moves offshore and low exits into Atlc
rain decreases then ends from SW-NE. Ridging builds in aloft and
high pressure at surface with deep layer dry air on Fri but
progressive pattern develops quickly next Wrn trough which begins
to move quickly Ewd progressively flattening Ern ridge with
steering flow becoming increasingly SWLY with rising temps. This
trough reaches Gulf region by Sun eve with some model differences
mainly in timing with GFS more progressive. The GFS drags a weak
cold front across Sun eve the ECMWF keeps front to our west thru
Will go with 0-30% PoPs SW-NE Thurs night...0-30% Fri...NIL POPS
rest of period except 40-20% NW-SE POPs on Sun with the front.
Highs upper 60s Fri...70 to 75 Sat thru Mon. Lows Thurs night
around 40 north to near 50 south...40-45 Fri night...near 50 Sat
and Sun nights.
It appears that winds and seas have peaked (around 15 KT with 2 to
4 ft seas), and all of the NWP guidance takes winds down to around
10 KT by this afternoon. As the pressure gradient tightens between a
wedge of high pressure to our northeast and a stalled front to our
south, east winds will increase to the 10 to 15 KT range overnight,
and continue through Thursday.
Relative humidity levels will remain above critical thresholds for
the foreseeable future. The only notable item is that dispersions
will remain quite low over the next couple of days.
Rainfall amounts from Monday were mostly a tenth of an inch or less,
and not enough to significantly alter local river/stream flows. A
series of upper level disturbances later today through Thursday will
deliver roughly an inch of rain (basin average) to much of the
region. This projected total is well below Flash Flood Guidance, so
flash flooding is not expected. The latest SREF and GFS based
hydrology ensembles (MMEFS) indicate that it`s likely that several
of our FL sites will go to action stage during the next week or so,
but are not expected to go to flood stage.
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.Preliminary Point Temps/PoPs...
Tallahassee 59 45 55 49 63 / 10 80 70 70 50
Panama City 59 47 59 51 62 / 20 80 70 70 40
Dothan 51 41 56 46 54 / 40 80 50 70 40
Albany 48 40 54 45 52 / 20 80 60 70 60
Valdosta 52 42 54 49 57 / 10 80 70 70 70
Cross City 66 49 65 55 68 / 0 80 60 70 70
Apalachicola 60 49 60 52 64 / 10 80 70 70 50