Area Forecast Discussion
Issued by NWS
FXUS62 KTAE 030804
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
304 AM EST Mon Mar 3 2014
.Near Term [Through Today]...
The upper level trough and associated surface cold front west of the
area continue to make steady progress eastward and will bring a
round of showers to most of the area today. Although the system
looks fairly impressive now on water vapor imagery, all of the
guidance forecasts gradual weakening through the day. Thus, only a
rather thin band of rain is expected to move across the area with
amounts generally staying below a quarter of an inch. The CAM
ensemble mean does forecast SBCAPE values roughly between 400-800
j/kg, so a rumble of thunder remains possible, but with the overall
weakening of the system, severe weather is not expected. Breezy
conditions are expected ahead of the front with gusts of 20-30 mph
today, especially if we can get some breaks in the cloud cover to
aid in mixing. Temperatures are expected to be non-diurnal today
across the western areas with steady or slowly falling temperatures
behind the front during the afternoon. However, the eastern half of
the area will likely get rather warm this afternoon ahead of the
front with mid to upper 70s expected. The official forecast avoided
using MOS guidance for temperatures today given the frontal passage
and stuck with an ensemble of raw model temperatures.
.Short Term [Tonight Through Wednesday]...
The GFS and ECMWF are in good agreement in forecasting a fast
500 mb flow pattern over the CONUS. From today through Thursday, the
average return period of a trough in our forecast area is about 36
hours. The rain will end quickly in North FL this evening as cooler,
much drier air advects into the region. However, the truly cold air
will remain well to the north, making a freeze unlikely (less than
20% chance) in our northwest zones. Patchy frost is possible there,
however. Lows will range from the mid 30s, to around 50 at Cross
City. Clouds will increase during the day on Wednesday as the next
trough approaches over the central Gulf Coast. With the increase in
clouds and a shallow cool airmass in place, highs will be rather
chilly (only lower to mid 50s) in GA and Al. Highs in FL will range
from the upper 50s (north and west of Tallahassee) to upper 60s
(around Cross City). The aforementioned trough will race east over
our region Tuesday night, bringing a chance of mostly light rain.
Lows will be in the upper 30s (north) to upper 40s south.
The forecast for Wednesday becomes more tricky due to detail
differences between the GFS and ECMWF. The GFS forecasts a temporary
dry period (between troughs), while the ECMWF continues the rain on
Wednesday. As is often the case with this type of forecast
divergence, we took an average of the two solutions, and forecast a
chance of rain (30-40%), mainly during the afternoon. Highs will
range from the lower 60s north to around 70 at Cross City.
.Long Term [Wednesday Night Through Monday]...
The main focus will be Thursday, when the next trough is scheduled
to move through our area. The GFS and ECMWF have come into much
better agreement with this system. Although it will be rather
impressive in terms of 500 mb height falls, neither model forecasts
the unusually strong surface cyclogenesis hinted at in previous
runs. The mean of the MSLP from all of the available NWP guidance
indicates an "average" intensity cyclone moving northeast across
North FL Thursday morning. Such a track would put all, or nearly
all, of our forecast area in the cool sector, greatly limiting the
threat of severe storms. The long term discussion issued later today
will address the remainder of the forecast period.
[Through 06Z Tuesday] A large area of IFR cigs with some patchy fog
has developed across the western two-thirds of the area. Increasing
southerly flow ahead of a cold front should keep visibility from
dropping too low for a significant length of time. Showers are
expected across the area as the front moves through today, and
although just enough instability may be present to support an
isolated thunderstorm or two, the chance of thunder appears too low
to include in any TAFs at this time. Clearing behind the front is
expected from west to east.
South winds around 10 KT this morning will shift to the northwest at
15 to 20 KT behind the cold front this afternoon, mainly over the
Panhandle coastal waters. Winds will become north around 15 KT over
the entire coastal waters overnight. Winds will be northeast to east
10 to 15 KT Tuesday and Wednesday.
Red flag conditions are unlikely this week. Showers are expected
across most of the area today as a cold front moves through,
although rainfall amounts will be light. Drier air is expected for
Tuesday, but RH will remain well above red flag levels. Rain chances
will increase significantly again by the middle of the week.
Although several rivers still exhibited above-normal stage/flow,
those that were recently at flood stage were continuing to decline.
Today`s basin average rainfall totals will be less than a quarter of
an inch, which should not have much of an impact. The QPF for
Tuesday night/early Wednesday will likely be even less. The GFS and
ECMWF have backed off on the QPF for Thursday`s system, and we now
think that basin average values will generally be less than one
inch. The latest GFS ensemble-based hydro forecast (MMEFS) does not
forecast any of our rivers to reach flood stage this week.
.Preliminary Point Temps/PoPs...
Tallahassee 78 43 62 44 64 / 60 10 10 30 30
Panama City 66 42 59 47 62 / 60 10 10 40 40
Dothan 65 36 54 41 64 / 80 0 20 40 20
Albany 65 38 54 38 62 / 80 10 10 40 20
Valdosta 78 41 58 42 62 / 70 10 10 30 30
Cross City 76 50 69 48 70 / 30 20 10 30 30
Apalachicola 69 43 61 48 62 / 50 10 10 30 40