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000
FXUS64 KSJT 071223
AFDSJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN ANGELO TX
625 AM CST SAT DEC 7 2013

.DISCUSSION...
Please see the aviation section below for discussion.

&&

.AVIATION...
Look for stratus and possibly freezing drizzle to slowly develop
across West Central Texas today, as boundary layer moisture
increases. The latest IR imagery indicate stratus is already
returning to our Interstate 10 corridor. With very cold air
remaining near the surface, warm moist air will glide up and over
this cold layer. This moist air will slowly increase the boundary
layer moisture, which will then produce a stratus deck. So, from
around noon today until around midnight tonight, some areas of West
Central Texas may have light freezing drizzle. After midnight
tonight, the potential for freezing drizzle will diminish for most
of West Central Texas, as drier air aloft moves over Texas.

Huber

&&

.PREV DISCUSSION... /ISSUED 347 AM CST SAT DEC 7 2013/

SHORT TERM...
Today and Tonight

West Central Texas may see patchy freezing drizzle this afternoon
through midnight tonight. Isentropic upglide may produce
patchy freezing drizzle beginning this afternoon across West central
Texas and continuing until around midnight tonight. Analysis of the
NAM 300K theta-e surface indicates moist upglide begins around noon
and continues until around midnight tonight. After midnight, the
isentropic lift becomes more neutral and available moisture
diminishes. If we do see freezing drizzle develop, I don`t
anticipate much if any accumulations. Surface cold air advection
will continue today with north to northeast surface winds around 10
mph. Thus, highs today will not warm much above sunrise
temperatures. For tonight, mostly cloudy to cloudy skies will
dominate. Surface winds will become more southeast after midnight
tonight. However, this will do little to prevent lows in the mid
teens for most areas, except across the Big Country where lows will
be around 10 degrees. Wind chill tonight along and north of our
Interstate 20 corridor will drop to around zero degrees after
midnight. That`s not as low as we see this morning; however, wind
chill around zero degrees requires appropriate precautions.

Huber

LONG TERM...
Sunday through Friday

Below normal temperatures are forecast Sunday through much of next
week for West Central Texas. A brief warm up is expected on Sunday
as surface high pressure shifts east, and southwest surface winds
return to the area. Still, highs will be well below seasonal
normals, ranging from the upper 30s across the northern Big Country,
to the mid 50s across the Interstate 10 corridor. In the meantime, a
potent upper level trough will swing across the Northern Plains,
sending the next shot of Arctic air into the region. I sided closer
to the faster ECMWF solution, as the models tend to be too slow with
these shallow/dense cold air masses. I expect stratus development
behind the front, which in combination with cold air advection,
should make for another chilly day across the area. Highs will range
from the upper 20s across the northern Big Country, to the mid 30s
for much of the Concho Valley, to near 40 across the Interstate 10
corridor. Low temperatures will be dependent on cloud cover on
Tuesday morning. The NAM is faster to clear the area out, while the
GFS hangs onto the clouds a bit longer. For now, I have indicated
clearing skies by morning, with lows generally in the teens to lower
20s. These lows could be a few degrees colder if we manage to clear
out a bit sooner. Cold air advection will continue on Tuesday, but
will be offset by daytime heating, which should allow temperatures
to climb back into the mid 30s to lower 40s.

The next weaker cold front is forecast to move through the region
late Wednesday/early Thursday. This should help to continue the
below normals temperatures, albeit warmer than what is forecast the
first part of the week. Highs both Wednesday and Thursday will be in
the 40s to near 50, while lows are generally in the 20s. Models
continue to advertise an upper level shortwave trough swinging
across the Desert Southwest Thursday, then across the Southern
Plains Friday. I kept a slight chance of showers across mainly the
eastern half of the area, where the better moisture will reside for
Thursday night/Friday. Beyond Friday, models diverge on the track of
the next upper level shortwave trough, so for now I have made little
changes beyond Friday. Below normal temperatures are still forecast
through the weekend.

Daniels

&&

.PRELIMINARY POINT TEMPS/POPS...
Abilene  19  11  42  20  30 /  10  10   5   5  10
San Angelo  23  15  50  25  35 /  10  10   5   5  10
Junction  30  15  54  26  40 /  10  10   5   5  20

&&

.SJT WATCHES/WARNINGS/ADVISORIES...
WIND CHILL ADVISORY until Noon CST today FOR THE FOLLOWING
ZONES: Callahan...Fisher...Haskell...Jones...Nolan...
Shackelford...Taylor...Throckmorton.

&&

$$

Huber/Daniels