Area Forecast Discussion
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FXUS62 KTAE 191409
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
909 AM EST Fri Dec 19 2014
.Near Term [Through Today]...
-- Changed Discussion --The morning analysis shows an upper level trough across Texas
approaching from the west and a warm frontal boundary oriented in a
west-east direction offshore of the northern Gulf coast. North of
this frontal boundary, a large area of light to moderate rain is
approaching from the west. Expect this rain will likely overspread
the western third of the area through the afternoon hours while
slowly weakening as the upper level shortwave gradually weakens.
PoPs are in the likely to categorical range across the western third
of the area, dropping to just 20% across the east and below 20%
across the southeast big bend. Highs will be coolest in the western
part of the area today with the highest coverage of light rain.
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.Prev Discussion [422 AM EST]...
-- Changed Discussion --.Short Term [Tonight Through Sunday]...
Primary zone of moderate isentropic ascent on the north side of
the weak Gulf low pressure area is expected to move across the far
northwestern portion of the forecast area overnight into Saturday
morning. By daybreak, the zone of best lift will be moving rapidly
east across Middle Georgia and into South Carolina. As a result,
rain chances should rapidly taper off after sunrise. However, the
models do indicate that some weak ascent with a moist low level
environment may be supportive of drizzle or possibly even some
light measurable precipitation, so will keep rain chances in the
forecast across northern areas on Saturday afternoon.
By Saturday night, focus will shift back to the southwest where
another storm system will be developing on a stalled frontal zone
across the Gulf. A large broad trough will be transiting from the
Rockies into the Central Plains Saturday night. With this system
moving quickly east into the Mid South on Sunday, expect
cloudiness and precipitation to develop quickly across the Eastern
Gulf and lift northward in a strong isentropic lift regime.
Numerical guidance typically under forecasts the intensity and
timing of this ascent by several hours, so have increased PoPs on
Sunday higher than the MOS. Some elevated instability late Sunday
afternoon may be supportive of isolated thunderstorms across the
.Long Term [Sunday Night Through Friday]...
At the start of the period, the trough will continue lifting NE
across the Southern Appalachians with the primary zone of
isentropic ascent shifting to the foothills. Even with the loss of
this lift, large scale QG forcing will likely be sufficient to
keep rainfall ongoing overnight, especially across the eastern
portion of the region. PoPs during this period have been increased
to the 70 to 80 percent range.
The region will effectively be between systems on Monday, but with
plenty of moisture still around, can`t completely rule out a
shower or two.
By Monday night and especially into Tuesday, rain will once again
return as the broad trough across the Central Plains further
amplifies and begins to shift eastward. Initially a frontal zone
will lift north back into the region on Tuesday focusing a
corridor of moderate to locally heavy rain Monday night and into
early Tuesday. By Tuesday afternoon, as stronger deep layer
forcing arrives, this surface boundary should retreat northward
into our region. Model guidance differs on how far northward this
boundary will get before a potent cold front surges across the
Gulf Coast States. For now, the warm front appears to set up
across North Central Florida, suggesting the environment most
favorable for surface-based convection would remain over Central
Florida. As a result, will only include Iso-T in the forecast for
Tuesday into Tuesday night. Nevertheless, this system bears
watching, not only for the heavy rainfall potential but for an
outside shot at severe weather if surface-based instability can
materialize in the strongly sheared environment.
[Through 12Z Saturday] Despite the BKN-OVC conditions that are
predominating the terminals overnight and will continue to do so for
the bulk of entire Taf Period, all of the Cigs are expected to
remain at VFR levels. Even the Vis is expected to hold at VFR for
most of the time period, with just a few interludes of MVFR level
Vis in a few of the showers.
Though winds may increase to 10 to 15 knots at times ahead of an
approaching weak low pressure area, headline conditions are not
expected through the weekend. Rainy conditions will develop by
Sunday afternoon and unsettled conditions will continue through
Tuesday. A significant increase in winds and seas are expected
after Tuesday with advisory conditions possible by Wednesday.
Plenty of clouds, low level moisture, and high rain chances will
inhibit any fire weather concerns over the next several days.
The initial system today and into Saturday is only expected to
produce up to a quarter of an inch of rain, which will have little
or no impact on area river levels. The combination of the storm
system on Sunday afternoon and the next system arriving on Tuesday
will signal an increase in flood potential, initially as an areal
flood threat in the Tuesday-Wednesday time frame with possible
river flooding to follow late in the week.
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.Preliminary Point Temps/PoPs...
-- Changed Discussion --Tallahassee 65 46 67 52 65 / 30 30 20 20 60
Panama City 61 50 65 55 63 / 60 40 20 20 70
Dothan 61 46 58 49 58 / 60 70 50 20 60
Albany 63 45 59 49 60 / 40 70 50 20 60
Valdosta 65 45 66 51 64 / 20 30 20 20 60
Cross City 70 44 69 54 69 / 10 10 10 20 60
Apalachicola 64 50 67 57 64 / 20 30 20 20 70
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