122512threat

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
727 AM EST Tue Dec 25 2012

…An Enhanced “Slight Risk” for Severe Thunderstorms continues
across the region Today and Tonight…

.NEAR TERM [Today and Tonight]…
Little change in thinking from the previous fcst package, as the
Intense Upper Level Shortwave continues its rapid dive to the SE
over TX early this morning. This vigorous shortwave has quickly
become convectively active during the past several hours, mainly
well to the east of its Center. Some signs of Sfc Cyclogenesis are
already apparent near the TX Gulf Coast, and it is this Sfc Low
which is expected to rapidly deepen and race off to our NE today and
tonight. Although the bulk of the severe weather is anticipated to
be associated with the pre-frontal squall line (and possible
fore-running discreet Supercells) tonight as it sweeps eastward
through the region, we are still a bit concerned for a secondary
severe weather threat during the day today. If this occurs, it will
likely be over western portions of the CWA (especially SE AL) where
the potential for Tornadic Supercells associated with the initial
Warm Front cannot be discounted. In any event, it should be
noted that the Storm Prediction Center has placed a 10% prob. for
Tornadoes which extends into Coffee county, and just clips Dale,
Geneva, and Walton as well, with a more typical 5% prob. extending
eastward across much of the remainder of the CWA. That said, the
primary threat from this system is still expected to be straight
line wind damage, with the potential for gusts between 60 and 75 mph
in the stronger storms…especially to the west of the Apalachicola
and Chattahoochee Rivers. This will be possible due to the highly
sheared (mostly speed shear tonight) environment, and decent low
level instability which will allow the stronger storms to mix some
of these winds to the Sfc. Therefore, all interests in the Tri-State
area are urged to keep abreast of the latest forecasts and updates
from the National Weather Service in Tallahassee on this rapidly
evolving event.

&&

.SHORT TERM [Wednesday Through Thursday]…
If the rapid fcst progression of this squall line continues to be
shown in the latest short term and hi-res model runs…this event
will be very close to ending in eastern portions of our CWA by 12-15
UTC on Wed. Another shot of cooler and drier air on gusty NW winds
will build into the region behind the Cold Front for mid week period.

&&

.LONG TERM [Thursday night through next Tuesday]…A progressive
pattern will remain in place through the period with the 25/00z GFS
and 25/00z ECMWF agreeing that the next rain maker will move into
the area on Saturday. This system currently does not look nearly as
impressive in terms of convective potential as the system we are
dealing with now, and the official forecast only carries a slight
chance of thunder close to the coast. For the most part,
temperatures are expected to be within a few degrees of the seasonal
averages, except cooler than average Thursday night as weak high
pressure temporarily builds in from the north.

&&

.AVIATION…
[Through 06z Wednesday] Areas of fog and low cigs will prevail
through sunrise with visibilities occasionally reaching airport
minimums. Fog is expected to dissipate quickly after sunrise with
breezy conditions developing during the afternoon hours. As a warm
front lifts northward, convection is expected to develop across the
area, some of which could be severe. Late in the period, a squall
line is expected to enter the region ahead of the cold front. This
may also be severe.

&&

.MARINE…Increasing onshore winds out ahead of a formative strong
low pressure system off to our west, will result in Small Craft
Advisory Conditions progressing from west to east across our Coastal
Waters this afternoon and evening. Then, as a very powerful squall
line develops out ahead of the approaching Cold Front tonight, Gale
Force winds (or frequent gusts) and seas will overtake the marine
area, with even stronger winds in the vicinity of any thunderstorms.
These Gale conditions will linger for a while out of the west behind
the Cold Front during the first half of Wednesday, before slightly
diminishing back to Advisory levels out of the northwest into
Wednesday night.

&&

.FIRE WEATHER…
There are no red flag concerns for the next several days with
wetting rain on the way.

&&

.HYDROLOGY…
Much of the region is expected to receive an additional 0.5 to 1.5
inches of rainfall during the next few days. This may cause some
minor rises along area rivers, but due to low flows in area basins,
no significant rises are expected at this time.