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Area Forecast Discussion

597
FXUS62 KTAE 250855
AFDTAE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
355 AM EST Tue Nov 25 2014

...Another Day and Night of Rain on Tap for Most Areas Along with
Cooler Temperatures...

.Near Term [Through Today]...
A band of moderate to heavy rain and embedded thunderstorms has
developed across our forecast area early this morning, just along a
surface cold front. The surface cold front will push southeast of
our area today, but rain will be maintained along the sloped frontal
surface to the northwest as a strong shortwave ejects east across
Texas. The response to the ejecting wave will be a strengthening
frontogenetic circulation - especially in the 18-00Z time frame.
Model consensus places the strongest 925-700mb UVV roughly right
where the rain band is already positioned as of 08Z - from Mexico
Beach, to Quincy, to Tifton, and 25-30 miles either side of that.
Rain should initially be quite focused in this narrow band, but will
eventually expand in coverage as 00Z approaches with cyclogenesis
commencing in the eastern Gulf of Mexico. During the daytime hours,
though, we expect a sharp gradient in rain chances due to some dry
low-level air working in behind the cold front. Model forecast cross
sections cut through the front across our area from NW-SE show a
wedge of drier air from roughly ECP-BIJ and to the northwest. This
should limit northwestward progress of measurable rain today,
although even our northwest zones should see some light rain by
tonight. Given the strength of the frontogenetic circulation and
precipitable water values about 1.5 to 2 standard deviations above
normal, it is likely we will see some heavy rain at times today,
particularly in the f-gen band. Heavy rain wording was added to the
forecast with 12-hr QPF of 1.0-1.5" on average in those areas. To
the southeast, scattered showers and thunderstorms should gradually
increase in coverage through the day as low-level ascent becomes
stronger with the developing surface low in the eastern Gulf.

We went with a non-diurnal temperature trend for today. Cooler air
will be working its way southeast across the area in the morning
behind the surface cold front. However, abundant cloud cover and
rain will likely maintain temperatures in the 50s for all but the
eastern Florida Big Bend. By 18-20Z, the coolest temperatures in our
area should be in the low 50s, roughly along the same rain band axis
described earlier (Mexico Beach - Quincy - Tifton). Therefore, highs
for a significant part of our area may occur early in the morning.
The hourly temperatures were a blend of the RAP and 4km NSSL-WRF.


.Short Term [Tonight Through Thursday]...
Isentropic ascent of the 300K surface will be strongest during the
hours centered around 00Z Wednesday as the front remains stalled
over the area under parallel southwesterly flow aloft. DPVA will
also be in play. Therefore, we start out with categorical PoPs
across the board, as high as 100% across roughly the eastern half of
the forecast area. After that, forcing for ascent will drop off
precipitously after midnight with all PoPs ending before 18Z
Wednesday. For additional rainfall totals and any flooding concerns,
see the hydrology section below.

As cyclogenesis jumps to the coastal Carolinas, the colder air will
finally be drawn completely across the forecast area tonight. In
fact, temperatures will be chilly throughout this period. Look for
low temps by dawn Wednesday to range from the upper 30s over
Southeast AL and adjacent portions of the FL Panhandle to the upper
40s across the Southeast FL Big Bend. Highs both Wednesday and
Thursday will generally be closer to what we see in January with
lowers 60s common. A few spots across our northern zones will not
even quite make it to 60. Overnight lows Wednesday night will
generally be in the mid to upper 30s inland with 40s near the coast.


.Long Term [Thursday Night Through Tuesday]...
This period will be dry with surface high pressure in control.
Heights will also rise with zonal flow in place from the weekend
into Monday. However, the chilly air mass will remain in place
through Friday night with temps near or below even normal midwinter
levels. A few spots across the northern fringe of the forecast area
could touch freezing Thursday night and there could be some frost
Friday night. A moderating trend is expected from the weekend into
Monday. Some areas will see lower 70s degrees by Sunday with most
areas getting there on Monday.

&&

.Aviation...
[Through 06Z Wednesday] In general, there was a gradient in
observed conditions as of TAF issuance time from VFR to the
northwest, to IFR to the southeast, across the area. We expect
that trend to continue through the day, although it is likely
model guidance is being too optimistic with CIGS. A steady, cool
rain is forecast at most of the terminals, and that should help
lower cloud bases. In general, we are forecasting CIGS to trend
down into IFR or low-end MVFR at TLH and VLD, and trend down to
MVFR at ECP and ABY. DHN is most likely to stay at VFR for much of
the period. Visibility may be briefly reduced into the IFR range
at times in heavier rain or thunderstorms.

&&

.Marine...
Small craft advisory conditions will first be achieved with offshore
winds speeds this morning. The nearshore legs will not see this
until later in the day. Winds will be strongest overnight and an
occasional gust to gale force will be possible. Conditions will drop
below advisory criteria, even offshore, Wednesday morning. After a
brief lull Wednesday afternoon, a return to cautionary conditions is
expected from Wednesday night into Friday. Winds will then drop
below headline criteria for Friday night and Saturday as they
finally veer to onshore.

&&

.Fire Weather...
Wetting rains are expected today with high RH. Drier air will arrive
on Wednesday and Thursday, but RH values are not currently forecast
to reach critical levels. Additionally, fuel moisture will be quite
high given recent rainfall.

&&

.Hydrology...
Radar estimates that 2.5-3.5 inch rainfall totals have been common
since Saturday across most of our GA zones as well as northern and
western portions of the FL Big Bend and adjacent Panhandle. This is
causing rises on most area rivers. These slow rises will continue
for the next several days. Additional rainfall totals through
tonight will be around 2-2.5 inches for the southeastern 1/2 of
the forecast area. These rains are not expected to cause
significant areal or riverine flooding. However, the Ochlockonee
River could approach minor flood stage in 4-5 days.

&&

.Preliminary Point Temps/PoPs...

Tallahassee   61  43  62  37  64 / 100 100  10  10   0
Panama City   57  44  63  45  63 / 100  90  10  10   0
Dothan        54  40  60  39  60 /  50  90  10  10   0
Albany        56  42  61  37  61 /  80 100  20  10   0
Valdosta      62  46  61  37  62 / 100 100  20  10   0
Cross City    68  49  64  37  65 /  90 100  20  10   0
Apalachicola  62  46  62  44  64 / 100 100  10  10   0

&&

.TAE Watches/Warnings/Advisories...

FL...None.
GA...None.
AL...None.
GM...Small Craft Advisory from 4 PM this afternoon to 7 AM EST
     Wednesday for Apalachee Bay-Coastal waters From Ochlockonee
     River to Apalachicola FL out to 20 NM-Coastal waters from
     Suwannee River to Keaton Beach FL out 20 NM-Coastal waters
     from Apalachicola to Destin FL out 20 NM.

     Small Craft Advisory until 10 AM EST Wednesday for Waters from
     Suwannee River to Apalachicola FL from 20 to 60 NM-Waters
     from Apalachicola to Destin FL from 20 to 60 NM.


&&

$$

NEAR TERM...LAMERS
SHORT TERM...WOOL
LONG TERM...WOOL
AVIATION...LAMERS
MARINE...WOOL
FIRE WEATHER...LAMERS
HYDROLOGY...WOOL






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