Area Forecast Discussion
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FXUS62 KTAE 301946
AFDTAE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
346 PM EDT Thu Oct 30 2014

.Near Term [Through Tonight]...

The cold front has pushed through the area with cooler and drier
air advecting in. The remaining cloud cover over the southeast
half of the area will rapidly clear out. Overnight lows tonight
will be cooler than recent nights with low to mid 40s across
portions of southeast Alabama and mid 40s to near 50 elsewhere.


.Short Term [Friday Through Saturday Night]...

An initial cold front has ushered in a drier air mass already
across the area; GOES blended precipitable water (PWAT) is
estimating around 0.50" in Tallahassee. The dry air mass that
will be in place on Friday should be sufficient to make the next
cold front passage late Friday afternoon to Friday evening a dry
one. This secondary cold front will be associated with a potent,
digging +PV anomaly on the back side of a broad eastern US trough.
As of 19Z today (Thursday), water vapor satellite indicated the
+PV anomaly over southeast Manitoba. The GFS analysis indicated
that the 1.5 PVU surface (dynamic tropopause) was down around
600mb, an indication that the digging wave is quite strong. By 12Z
Saturday, the model consensus places a closed mid-level low over
South Carolina with height anomalies around 5-6 standard
deviations below normal. In meteorological parlance, this is quite
unusual. With a deep and potent developing autumn cyclone for the
Southeast region, one would expect strong cold air advection and
windy conditions to the west of the low, behind the surface cold
front. The standardized anomalies bear this out as well: over our
forecast area models project the 850mb temperature anomalies peak
at 4-5 standard deviations below normal, and the 850mb wind speeds
peak nearly 3 standard deviations above normal.

These signals suggest that the outer tails of the guidance
distribution may actually be plausible scenarios in this case.
With respect to temperatures, we expect this could produce high
temperatures on Saturday that are very close to record cool
values. The record for coolest high temperature on November 1st in
Tallahassee is 57. The current forecast calls for 59 at TLH, with
mid-upper 50s elsewhere, so it should be close. The model blend
that we utilized for Friday Night and Saturday was weighted more
toward raw model guidance (instead of MOS) as that tends to
perform better in strong cold air advection regimes. For Saturday
Night, winds should begin to decrease but the surface ridge axis
will remain west of our forecast area with the high centered near
the Ohio River. This should maintain some light winds and mixing
through the night, so the low temperature forecast calls for
values close to the consensus (mid 30s). If the winds can diminish
sufficiently late Saturday Night, areas of frost would be more
likely and a Frost Advisory may become necessary. Wind chills on
Friday Night and Saturday Night should be in the low-mid 30s.

Regarding winds on Saturday, we could approach Wind Advisory
criteria. The anomalously strong winds near the top of the
boundary layer should lead to higher wind gusts than we see behind
most cool-season cold fronts. For now we have indicated wind gusts
of 30-40 mph in the forecast, but some BUFKIT soundings
(especially with the GFS) indicate the potential for gusts in
excess of 40 mph depending on how deep the mixed layer is.


.Long Term [Sunday Through Thursday]...

The extended forecast will be marked by gradually moderating
temperatures and mostly dry weather as a mid-upper level ridge
builds across the eastern US and we transition into more of a
+NAO/+AO regime. Highs should be closer to 80 degrees by the
middle of next week. The next chance of rain is expected to hold
off until Wednesday at the earliest.

&&

.Aviation...

[Through 18z Friday] VFR conditions are expected to prevail
through the period with light winds.

&&

.Marine...

In the wake of the secondary cold front on Friday evening, we
expect at least widespread advisory conditions with winds
increasing to around 25 knots in most of the coastal waters. Given
the strength of the wind field just above the surface and the warm
early autumn water temperatures, frequent gale force gusts will be
a distinct possibility. The much colder-than-normal air mass will
combine with sea-surface temperatures that are above-normal to
produce unusually steep lapse rates in the marine boundary layer.
This should provide for efficient transfer of stronger winds to
the water surface, and model consensus indicates these could be as
high as 40-45 knots near the top of the boundary layer. Given the
anomalous situation, we have issued a Gale Watch for all of the
coastal waters from Friday Night into much of Saturday. Winds
should subside later in the weekend, but periodic easterly winds
at SCEC levels should persist into early next week.

&&

.Fire Weather...

A much colder and drier air mass will push into the region over
the weekend and bring high transport winds along with it. Red
flag conditions are possible, particularly Saturday and Sunday,
although the lower temperatures may keep our relative humidity
values just shy of criteria.

&&

.Hydrology...

Dry conditions are expected over the next several days, with no
impacts expected along area rivers and streams.

&&

.Preliminary Point Temps/PoPs...

Tallahassee   45  75  41  59  37 /   0   0   0   0   0
Panama City   52  72  45  59  42 /   0   0   0   0   0
Dothan        44  72  38  57  35 /   0   0   0   0   0
Albany        45  72  39  57  36 /   0   0   0   0   0
Valdosta      47  73  40  58  37 /   0   0   0   0   0
Cross City    50  75  45  59  37 /  10   0   0   0   0
Apalachicola  52  74  46  59  43 /   0   0   0   0   0

&&

.TAE Watches/Warnings/Advisories...

FL...None.
GA...None.
AL...None.

GM...Gale Watch from Friday evening through Saturday afternoon for
     Destin FL to Suwannee River out to 60 NM.


&&

$$

NEAR TERM...DVD
SHORT TERM...LAMERS
LONG TERM...LAMERS
AVIATION...DVD
MARINE...LAMERS
FIRE WEATHER...MOORE
HYDROLOGY...HARRIGAN






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