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974
FXUS64 KSJT 230349
AFDSJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN ANGELO TX
949 PM CST Mon Dec 22 2014

.UPDATE...
Updated to add a mention of a rain/snow mix to portions of the
western Big Country and western Concho Valley.

&&

.DISCUSSION...

Radars continue to show a large band of precipitation moving
across the Panhandle and South Plains into the Big Country north
of I-20 this evening. Definitely as a snow look to some of it
already, although temperatures are way too warm to support it.
However, colder air filtering in behind the front will combine
with some wet bulbing to allow temperatures to drop by sunrise.
Soundings suggest that the precipitation will almost assuredly be
all snow above the surface across much of the area, and its just a
matter of getting temperatures in the lowest 500 to 1000 feet cold
enough to allow some of the snow to reach the ground. That still
looks pretty tough across most of the area, but the area from
Sweetwater to Sterling City will see the chance. Elevations in
those areas are 500 feet or so higher than the surrounding areas,
and that may make all the difference.

Have introduce a rain/snow mix to the forecast for those areas by
morning. Ground temperatures are very warm, and surface
temperatures likely to stay above freezing so don`t anticipate any
real issues from whatever snow does fall.

If temperatures cool even a little more than anticiapted, may have
to bring a mention of a rain/snow mix into Abilene and San Angelo
as well. Will continue to monitor.


&&

.PREV DISCUSSION... /ISSUED 539 PM CST Mon Dec 22 2014/

AVIATION...
/00Z TAFS/

Scattered showers and post frontal MVFR stratus will be
developing late tonight and Tuesday morning over West Central
Texas. There is a chance for IFR ceilings, particularly at KABI
Tuesday morning, but models vary on the potential, so will keep
as MVFR at this issuance. Most of the showers will be move east
in the early afternoon, with VFR condition returning mid to late
afternoon.

PREV DISCUSSION... /ISSUED 326 PM CST Mon Dec 22 2014/

SHORT TERM...
(Tonight and Tuesday)

An active weather pattern is in store for the next 24 hours. A cold
front is moving through the area today, and will be through all of
West Central Texas by this evening. An upper level trough currently
across the Plains will strengthen and send a short wave trough
across West Central Texas late this evening/early Tuesday morning.
This is indicated by most of the high resolution models, with
showers developing across the Big Country late this evening, then
moving across at least the northern two thirds of the area during
the early morning hours. The likely PoPs were expanded south into
the northern Concho Valley and Heartland, with chance PoPs down to
the Interstate 10 corridor.

Temperatures overnight will drop into the upper 30s to lower 40s
across all of West Central Texas. As the midnight shift mentioned in
the previous discussion, temperatures from the surface to about 2500
or 3000 feet will be above freezing, so mainly rain is expected. A
brief change over to a mix of rain/snow will be possible across
parts of the Concho Valley/Big Country, but confidence remains low,
so all rain was continued in the forecast. Even if we did see a few
snow flakes, no accumulation is expected.

Our next chance of precipitation will be Tuesday morning, as the
main upper level trough axis swings across the region. High
resolution models continue to indicate an area of light to moderate
rainfall developing across the Big Country and then swinging across
the Concho Valley and Heartland Tuesday morning. Rain chances will
decrease from northwest to southeast during the afternoon, with most
precipitation east of the area by sunset. Rainfall accumulations
through the next 24 hours will likely be less than one quarter inch,
with isolated amounts of up to one half inch possible.

Daniels

LONG TERM...
(Tuesday night through Monday)

As the trough continues to migrate east across the CONUS, northerly
winds will persist and keep West Central Texas near normal
Wednesday. Expect afternoon highs to be in the low 50s with
overnight lows near freezing.

Expect Christmas Day to be warm and breezy as moderate ridging will
quickly give way to lee cyclogenesis. This will induce southwest
winds causing warmer, drier air, leading to afternoon high
temperatures mainly in the 60s. Winds are expected to reach speeds
between 20-25 mph in response to a strengthening surface level
pressure gradient.

Forecast models have slowed the trough and, consequently, the
passage of the cold front by about a day. The EC model brings the
northerly wind shift and cold air advection across the area late
Friday evening/Saturday morning. Expect much cooler temperatures on
Saturday with highs mainly in the 40s and 50s with overnight lows in
the upper 20s and lower 30s. The EC has decent precipitation across
portions of West Central Texas and moisture return flow looks
adequate for precipitation. Thus, added slight chance pops on
Saturday to accompany the passage of the cold front. There is an
outside chance for some frozen precipitation across the Big Country,
however, kept liquid precip only at this time.

Finally, early next week some isentropic lift will bring a slight
chance of precipitation, mainly across the Northwest Hill Country
and Heartland. Temperatures are expected to be above seasonal normal
and therefore no frozen precipitation is anticipated.

JMD

&&

.PRELIMINARY POINT TEMPS/POPS...
Abilene  37  48  33  50  32 /  70  50   0   0   0
San Angelo  39  49  33  52  30 /  50  50   5   0   0
Junction  41  51  32  54  28 /  20  40   5   0   0

&&

.SJT WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

07






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