Area Forecast Discussion
Issued by NWS San Angelo, TX

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FXUS64 KSJT 202312
AFDSJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN ANGELO TX
612 PM CDT MON OCT 20 2014

.AVIATION...
/00Z TAFS/
Expect VFR conditions at the terminals the 24 hours. The winds
will be east to southeast at less than 10 knots.

&&

.PREV DISCUSSION... /ISSUED 346 PM CDT MON OCT 20 2014/

SHORT TERM...
(Tonight and Tuesday)

At mid-afternoon, a weak upper low was over extreme northwestern
Chihuahua Province in Mexico, just south of the border with
Arizona and New Mexico. A minor lead shortwave ahead of the low
was entering southwestern Texas. This has generated widely
scattered showers across the Trans-Pecos and into our southwestern
counties, where the airmass is weakly unstable. The upper low will
open into a trough and lift northeast across West Texas during the
day Tuesday. The better rain chances with this system will remain
west of our area. We are carrying 20-30 PoPs for showers and
thunderstorms tonight across the area west of a Sterling City to
Sonora line. Have expanded the slight chance PoP north on Tuesday
to include Sterling County and the western parts of Fisher and
Nolan Counties. Across the rest of our area, the cumulus field
this afternoon will dissipate during the evening, followed by some
increase in high and middle cloud cover from the southwest
overnight into Tuesday. Have a potential for some patchy light fog
to develop across our east-central and southeastern counties by
early Tuesday morning, but this will depend on the extent of cloud
cover/duration of clearing. Little temperature change is expected
with overnight lows and afternoon highs through Tuesday.

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LONG TERM...
(Tuesday night through Monday)

The closed upper-level cyclone over the Desert Southwest will
slowly open up and lift northeast over the next 36 hours,
weakening as it moves into the Plains and is absorbed into the
northern stream. Weak ascent will be maintained through Tuesday
evening, but should wane as the trough continues to dampen.
Isolated showers and thunderstorms will be possible over the far
southwestern portion of the CWA early in the Tuesday night period.
However, with sunset around 7 PM, the earlier loss of surface
heating should preclude convection lasting past 03z.

By midweek, the potent trough currently moving ashore over the
Pacific Northwest will be moving east into the Plains. The model
consensus keeps the primary ascent focused over the northern and
central Plains, but we should see some synoptic scale lift
Wednesday into early Thursday as the southern extent of the trough
axis makes its way across the region. As was the case 24 hours
ago, the ECMWF and GEM are a bit more amplified with this trough,
whereas the GFS depicts a less pronounced wave. PoPs were
maintained in the 20-30% range Wednesday afternoon and night, with
the best rain chances across the western Concho Valley and Big
Country.

These same models are all producing light QPF across the area on
Thursday, but confidence is somewhat low giving the forecast
location of the departing trough. Slight chance PoPs were retained
areawide. The weak cold front that was advertised yesterday by the
ECMWF and GEM is no longer in their respective solutions, with
southerly flow maintained throughout the week. This will keep
temperatures in the upper 70s to lower 80s both Wednesday and
Thursday, warming as we head into the weekend.

By Friday, we should be on the subsident side of the trough with a
transient mid-level ridge traversing the central CONUS. Expect
mostly sunny skies and above normal temperatures. Afternoon highs
are forecast to be in the low to mid 80s Friday through Sunday.
The medium range models differ in the evolution of the pattern by
early next week, but the consensus is that a trough will move
across the western states Sunday into Monday. Given the model
disparity, confidence is low regarding the forecast by Monday.

Johnson

&&

.PRELIMINARY POINT TEMPS/POPS...
Abilene  57  79  56  77  57 /   5   5   5  20  30
San Angelo  56  79  55  78  56 /  10  10  10  20  20
Junction  56  79  53  81  57 /   5  10   5  10  10

&&

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

$$

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