Area Forecast Discussion
Issued by NWS San Angelo, TX

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FXUS64 KSJT 031826
AFDSJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN ANGELO TX
1226 PM CST Tue Mar 3 2015

.AVIATION...
/18Z TAFS/

Expect gradual improvement into VFR ranges across West Central
Texas this afternoon; but, MVFR ceilings return south overnight.
Models indicate ceilings will continue to improve this afternoon.
As for MVFR ceilings returning overnight, confidence is moderate
for the Sonora, Junction, and Brady terminals. For the San Angelo
and Abilene terminals, confidence is low for MVFR ceilings
returning overnight.

Huber

&&

.PREV DISCUSSION... /ISSUED 544 AM CST Tue Mar 3 2015/

AVIATION...
/12Z TAFS/

Visibilities fell as low as 1/4 mile earlier this morning, but
have since improved across much of the CWA. However, ceilings
remain IFR or lower for the most part. These ceilings will slowly
improve this morning and are expected to lift by 18z. Southwest
winds are expected to develop this morning, occasionally gusting
around 20 kts through mid-afternoon. After 20z, wind speeds are
forecast to diminish due to the proximity of a surface trough.
Expect light and variable winds overnight, but a strong cold
front will be approaching KABI by 12z. Rain chances will increase
overnight, but should have minimal operational impact.

Johnson

PREV DISCUSSION... /ISSUED 427 AM CST Tue Mar 3 2015/

SHORT TERM...
(Today and tonight)

Low clouds, drizzle, and fog continue across West Central TX
early this morning. Visibilities have fallen to 1/2 mile or less
at many observation sites, prompting a Dense Fog Advisory through
mid-morning. Visibilities will likely improve after sunrise and
the advisory may end up being canceled early. We`ll hang on to the
low clouds through the day, but the drizzle and fog should
diminish by noon as low-level winds veer to the southwest.

The models have been zealous in mixing out this wedge of cold air
the past few days, and today`s runs are no exception. Temperatures
at 850 mb are still progged to warm to 14-16C this afternoon, a
jump of 6-8C from Monday. This would normally suggest to a warm-up
of 10-15F, but mixing heights yesterday remained well below 900
mb. Despite the run of cold weather, we still anticipate
temperatures taking quite a leap forward today, topping out in
the mid 60s to around 70 degrees. There is some bust potential
with this temperature forecast. If low clouds remain stubborn, we
could be a good 10 degrees cooler. In addition, the downslope
component of the low-level winds is not optimal and wind speeds
are relatively weak during the afternoon hours due to the
proximity of a surface trough.

This surface trough looks to sit over the Big Country this
evening, eventually giving way to the next arctic cold front. This
front is forecast to reach I-20 by 12z, ushering in strong north
winds and much colder air. Ahead of this front, elevated
convection will be possible as a shortwave trough approaches west
TX. Thunder was retained overnight for all zones, with a decent
chance for showers (with the best chances in the northern zones).

Johnson

LONG TERM...
(Wednesday through Monday)

The focus in the long term will continue to be the much colder
air, and precipitation moving into the area Wednesday/Wednesday
night.

The next arctic front will be moving south through the forecast
area at the beginning of the long term forecast period. Will go
with the faster GFS/ECMWF timing of the cold front as opposed to
the slower NAM. With an arctic air mass like this, would expect
the front to be faster rather than slower. Expect the front to be
near the I-20 corridor by early Wednesday morning, through the
Concho Valley by noon, and through the I-10 corridor by the
evening hours. As this front moves through, the upper level low
currently off the southern coast of California will be lifting
northeast towards the area as an open wave. As the wave
approaches, upper level lift will move into the area. We will be
underneath the right entrance region of a 170+ knot jet streak
extending into the Great Lakes region. In addition, 850mb-700mb
frontogenetical forcing will move south through the area behind
the surface cold front. These factors will combine to give the
area a good chance for precipitation, and with the elevated
instability, we may see some thunderstorms as well. Have kept the
chance for thunderstorms confined mainly to southern areas for
now, although a few lightning strikes farther north cannot be
ruled out. The timing for the best chances for precipitation will
be during the day Wednesday. Wednesday night, the dry slot will
move in over the area wrapping around the southern end of the low,
effectively ending precipitation between midnight and 6 AM
Thursday.

The main challenge associated with the precipitation will be what
type. Have not made any wholesale changes to the inherited
forecast. With the front moving through during the day, expect
highs to be reach during the morning hours across the Big Country,
and mid-day farther south. Temperatures will fall rapidly behind
the front, and possibly below freezing for the Big Country during
the afternoon hours. Vertical profiles rapidly cool as well,
suggesting a change from liquid precipitation to a wintry mix by
late morning for the Big Country that could include sleet, snow,
and/or freezing rain. Will not try to get too clever with
precipitation type at this point, so have kept mainly a rain/sleet
mix, changing to sleet/snow during the afternoon and evening
hours. Then overnight, mainly snow is expected, except for the
I-10 corridor where either a mix of sleet and snow, or freezing
drizzle will be possible. Will keep just a slight chance of snow
or sleet after midnight, and move most of the precipitation out of
the area by Thursday morning.

Thursday will be cold as well as this air mass will likely hang
around for at least one more day under cloudy skies, and continue
northeasterly surface flow. Highs Thursday will only reach the
upper 30s to lower 40s. Lows during this time period will be
mainly in the 20s. By Friday, we should see begin a warming trend,
and possibly some peeks at the sun. On Saturday, another cold
front is expected, but this front is not expected to be anywhere
near as strong as Wednesday`s, and should just temporarily slow
the warm-up down a little bit. Expect temperatures back into the
60s by Sunday.

20

&&

.PRELIMINARY POINT TEMPS/POPS...
Abilene  41  45  21  36  21 /  50  70  30  10   5
San Angelo  48  52  25  40  23 /  30  60  40  10   5
Junction  50  60  28  39  23 /  30  60  60  10   5

&&

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

$$






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