Area Forecast Discussion
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FXUS62 KTAE 300005
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
805 PM EDT Wed Oct 29 2014
.Near Term [Through Tonight]...
-- Changed Discussion --Regional 23Z surface analysis shows the weakening cold front to
stretch across southern Alabama roughly from Mobile northeast to
Eufala, then across central Georgia and the western Carolinas.
Showers and scattered thunderstorms ahead of this front are still
going this evening, but are expected to become mostly dissipated by
around midnight. Lows tonight will be in the upper 40s to around 50
in southeast Alabama, 50s to around 60 everywhere else with the
warmest temperatures in our southeastern zones. In these
southeastern zones ahead of the front where the temperatures will
be warmer, moisture will also be higher. Patchy fog will be
possible in this area during the early morning hours, clearing up
a little after sunrise.
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-- Changed Discussion --[Through 00Z Thursday] VFR is expected to prevail through the period
with the exception of VLD, where fog may be possible once again in
the early morning hours. Winds tomorrow will be from the north at
around 10 knots.
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.Prev Discussion [403 PM EDT]...
-- Changed Discussion --.Short Term [Thursday Through Friday Night]...
The aforementioned cold front should push south of the forecast
area either late tonight or Thursday morning. There may be some
lingering showers 12-18Z Thursday near the surface cold front, but
significant dry air advection is expected through the day, so a
mostly dry forecast is expected and clouds should quickly clear
out. The boundary layer temperatures should not decrease much
behind the initial cold front, and therefore highs on Thursday
are expected to be close to normal (mid-upper 70s). Continued
clear skies and dry weather are expected into Friday with slightly
below normal temperatures.
A more substantial cold front is expected to arrive Friday
evening, associated with a potent, digging +PV anomaly on the
backside of a broad trough in the eastern United States. By 12Z
Saturday, the latest operational ECMWF and GFS generate sub-538
DKM closed low at 500mb near South Carolina with the digging +PV
anomaly aloft. This is highly anomalous for late October, around 5
standard deviations below normal. In fact, many fields on the
latest numerical model runs are quite anomalous in the Southeast.
For example, the GEFS ensemble mean forecast 850mb temperatures at
12Z Saturday are 4-5 standard deviations below normal across south
Georgia. In other words, this should be a stronger cold front
than normal for early October, despite the fact that no
precipitation is expected with the front. Because of this we have
trended temperatures down for Friday Night with lows generally
between 40 and 45 degrees. However, there should be a limit to how
cold the air temperature can get as a strong pressure gradient
should keep near-surface winds and boundary layer mixing up
overnight. Therefore the forecast reflects lows several degrees
below the multi-model consensus.
.Long Term [Saturday Through Wednesday]...
Strong cold air advection will continue on Saturday, which should
produce daytime maximum temperatures well below normal. The record
coolest max temp on November 1st at Tallahassee was 57 in 1993. We
could get close to that sort of value on Saturday given the highly
anomalous low-level temperature profile. The raw GFS and ECMWF
have highs of 55 and 56 respectively, but most MOS guidance is in
the low 60s. We trended the high temperature forecast down with
increasing confidence in an anomalously cool air mass, but not as
extreme as some of the raw model guidance for now.
For Saturday Night, the surface ridge axis should drift closer
which will lead to lighter boundary layer winds and reduced
mixing. This should create the coldest night of the forecast
period with lows away from the coast in the mid-upper 30s. This
could be our first shot at frost of the winter season, but RH
values could be a little too low for widespread frost. After that,
a building ridge in the eastern US and transition to a +NAO/+AO
state will lead to a gradual moderation in temperatures into
next week with continued dry weather.
A slight increase in offshore winds tonight behind a cold front
has prompted a SCEC headline over the western half of the coastal
waters with 15-20 knot winds. Otherwise, conditions should be
relatively benign until a stronger cold front arrives on Friday
evening. Advisory level winds are likely, and a few gale (34kt)
force gusts cannot be ruled out. With warm water temperatures, and
an unusually cold low-level air mass just above the surface, lapse
rates over the waters should be very steep and support efficient
transfer of stronger winds aloft to the surface. Later in the
weekend and into next week, winds should veer to the east and
periodic SCEC conditions are possible - especially at night.
Red flag criteria are not forecast to be met until Saturday in the
wake of a dry cold front. On Saturday, much of the tri-state
area will likely see red flag conditions. Saturday will mark the
return to cool season criteria in Alabama.
Rainfall amounts through tonight are expected to be mainly on the
light side with no impact to rivers and streams expected over
the next several days.
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.Preliminary Point Temps/PoPs...
Tallahassee 60 78 46 75 44 / 30 10 0 0 0
Panama City 61 74 52 73 47 / 30 10 0 0 0
Dothan 50 73 44 73 40 / 30 0 0 0 0
Albany 52 74 44 73 41 / 30 0 0 0 0
Valdosta 57 77 49 73 44 / 30 10 0 0 0
Cross City 62 81 54 76 48 / 10 20 10 0 0
Apalachicola 62 77 51 74 49 / 20 10 0 0 0