Area Forecast Discussion
Issued by NWS
FXUS62 KTAE 310028
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
828 PM EDT Thu Oct 30 2014
.Near Term [Through Tonight]...
Regional 00Z surface analysis shows the cold front stretching from
Jacksonville southwestward across Gainesville to just south of Cedar
Key. Local radar imagery shows the showers associated with this
front have also cleared the area. As colder, drier air mass makes
its way into the area tonight, skies will clear and temperatures
will drop noticeably. Lows will be in the low to mid 40s over most
of the area, upper 40s to around 50 along the immediate coast and in
SW Georgia and the eastern Big Bend.
[Through 00Z Saturday] VFR conditions will prevail through the
period. Winds will be from the NNW, picking up to around 10 knots
.Prev Discussion [346 PM EDT]...
.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.
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.
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.
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
GM...Gale Watch from Friday evening through Saturday afternoon 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-Waters from Suwannee
River to Apalachicola FL from 20 to 60 NM-Waters from
Apalachicola to Destin FL from 20 to 60 NM.