Area Forecast Discussion
Issued by NWS San Angelo, TX

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FXUS64 KSJT 040555 AAC
AFDSJT

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE SAN ANGELO TX
1155 PM CST Tue Mar 3 2015

.AVIATION...
/06Z TAFS/

Rain showers are increasing in coverage across the northwest half
of west central Texas, while low clouds are developing across
southern and eastern sections. Expect a continuation of these
trends overnight. Carrying low cloud ceilings 800-1100 ft at
our southern TAF sites, and mentioning showers at KABI and KSJT.
A strong cold front will push south across west central Texas on
Wednesday. This front is expected to reach KABI shortly before
13Z, KSJT by 16Z, and the I-10 corridor by or shortly after 19Z.
Generally light winds will occur ahead of the front. Although
gusty north winds will follow passage of this front, the stronger
winds and gusts will occur several hours after the frontal passage.
Rain is expected early in the afternoon. As cold air deepens, the
precipitation type will make a southward transition to freezing
rain/sleet through the evening. Farther north across the Big
Country, a sleet to snow transition is expected by late Wednesday
evening. Ceilings will visibilities will drop through the
afternoon and evening, in the post-frontal precipitation. By 03Z,
carrying snow/sleet at KABI, freezing rain/sleet at KSJT, and
freezing rain at KSOA and KJCT.

19

&&

.PREV DISCUSSION... /ISSUED 946 PM CST Tue Mar 3 2015/

DISCUSSION...

Updated to issue a Winter Weather Advisory for Wednesday afternoon
and Wednesday Night for the Big Country, along and north of I-20
from Sweetwater to Abilene. New guidance continues to indicate
that the freezing line will drop south into the Big Country by mid
to late afternoon, in the heart of the precip shield. Soundings at
Abilene indicate a freeing rain and perhaps sleet setup,
eventually changing over to snow during the evening. Bumped
precipitation chances up and tweaked hourly temperatures to
account.

Indications are that wintry precip may well cover a large part of
West Central Texas by tomorrow evening. Will let the next shift
peruse the entire set of data, but would not surprise me to see
the advisory shifted south.

PREV DISCUSSION... /ISSUED 600 PM CST Tue Mar 3 2015/

AVIATION...
/18Z TAFS/

The low clouds have cleared out and VFR conditions have returned,
but this will not last much longer. After Midnight, low cloud
development with MVFR ceilings will affect our southern TAF sites.
Scattered showers and thunderstorms will develop late tonight and
continue into Wednesday morning. The KABI terminal will most likely
be affected. A strong cold front will push south across west central
Texas on Wednesday. This front is expected to reach KABI shortly
before 12Z, KSJT by 16Z, and the I-10 corridor around 19Z. Geherally
light winds will occur ahead of the front, and gusty north winds
will follow passage of this front. Rain will increase in coverage
during the afternoon, becoming freezing rain across the Big Country.
Ceilings will drop through the afternoon. with some visibility
reduction.

PREV DISCUSSION... /ISSUED 356 PM CST TUE MAR 3 2015/

SHORT TERM...
(Tonight and Tomorrow)

Look for big weather changes during the next 24 hours. As a minor
upper-level disturbance moves over West Central Texas tonight, it
will bring the potential for showers and perhaps some thunderstorms.
The best chance for showers and thunderstorms will be mainly along
and north of our Interstate 20 corridor, with more favorable upper
dynamics there. In addition, low clouds will return to much of West
Central Texas overnight, as another cold front approaches from the
north. Timing of this front is critical, with respect to when winter
type precipitation will begin tomorrow. Models continue to bring the
cold front to our Interstate 20 corridor by 6 am CST tomorrow
morning. So, with that timing, we believe the winter precipitation
will not begin until tomorrow afternoon, for locations along and
north of a Mertzon, to San Angelo, to Spring Creek line. Plus, we
believe accumulation of sleet of ice will not begin until after 6 PM
CST tomorrow evening, because surface cold air advection behind the
front will not be strong enough to lower surface temperatures to or
below the freezing mark.

LONG TERM...
(Wednesday night through next Tuesday)

Another blast of winter weather will affect all of West Central
Texas in the Wednesday night/Thursday morning time frame. Cold air
will continue to deepen across the area, with soundings showing most
areas having changed to an all winter precipitation type by
midnight. Taking a closer look at these soundings, a wedge of
warm air is seen between three-six thousand feet above the surface,
with sub-freezing air above and below this layer. This warm layer
barely reaches +3 Celsius, and the top of the saturated layer barely
touches -10/-11 Celsius (just below the dendrite growth zone). Given
this type of sounding profile, the forecast was changed to show
freezing rain as the predominant precipitation type. Some sleet
could also mix in at times, especially with any elevated convection
which develops, as the soundings show elevated instability
developing with MUCAPEs approaching 100 J/kg in the 700-450mb layer.

By Thursday afternoon, dry air will rapidly advect into the area,
allowing skies to become partly sunny from northwest to southeast
across the region. However, temperatures will be slow to recover
with most areas remaining in the 30s. Heading through the remainder
of the week and into the weekend, temperatures will continue to
moderate by 5 to 10 degrees Fahrenheit each day, with highs
approaching 60 degrees by Sunday, and remain in the 60s for the
first half of the work week.

&&

.PRELIMINARY POINT TEMPS/POPS...
Abilene  47  49  21  35  21 /  50  80  80  10   5
San Angelo  50  57  25  39  23 /  50  60  60  10   5
Junction  50  63  28  38  23 /  30  60  60  20   5

&&

.SJT WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY from 3 PM Wednesday to 6 AM CST Thursday
FOR THE FOLLOWING ZONES: Callahan...Fisher...Haskell...Jones...
Nolan...Shackelford...Taylor...Throckmorton.

&&

$$






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