Area Forecast Discussion
Issued by NWS San Angelo, TX

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FXUS64 KSJT 212042
AFDSJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN ANGELO TX
342 PM CDT TUE OCT 21 2014

.SHORT TERM...
(Tonight and Wednesday)

An upper trough is over the southern Rockies this afternoon, with
a lead disturbance lifting north across West Texas. The trough
axis will gradually shift east into West Texas on Wednesday. Based
on the track of the system and moisture fields, still expecting
the better rain chances to remain west of our area with this
system. Carrying slight chance PoPs tonight west of a Sterling
City to Ozona line, and 20-30 PoPs Wednesday across roughly the
western half of our area. Abilene and San Angelo will be near the
eastern edge of where we are carrying low PoPs Wednesday. Little
temperature change is expected with the overnight lows and
afternoon highs through Wednesday. Skies will be mostly cloudy
across the western part of our area, and partly cloudy to the
east.

19

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

A shortwave trough will be moving across the northern/central
Plains Wednesday night into Thursday, with a trailing trough
axis extending SSW into the Southern Plains. Synoptic scale ascent
associated with this trough axis will exist over the area early in
the period, but lift will wane by Thursday morning as the trough
axis moves east. PoPs were kept in the 20-30% range across the
western and central portions of the CWA Wednesday night, but
trimmed back slightly on Thursday, removing rain chances from
extreme northwest areas. It seems likely that Thursday rain
chances may need to be trimmed further if the current trends
continue.

An upper-level ridge will overspread the region in the wake of the
departing trough, providing tranquil weather conditions through
the weekend. Temperatures will follow a warming trend Friday
through Sunday as mid-level heights climb (500 mb heights near 591
dam). The ridge will be transient, as a deep trough digs over the
western CONUS during the latter half of the weekend. Southerly
winds will persist through early next week, ramping up to 10-20
mph on Sunday as southwesterly flow aloft increases ahead of the
aforementioned trough. As mid-level southwesterly flow moves
across the Mexican Plateau, we`ll see mid-level temps warm,
causing the elevated mixed layer (EML) to overspread the area.
This will result in a building thermal ridge over West TX Sunday
and Monday. Forecast high temperatures for this time are generally
in the mid 80s, but if we see southwesterly low-level flow
develop, compressional heating via downslope winds will likely
push temps to near or slightly above 90 degrees.

The GFS, ECMWF, and GEM are all in pretty good agreement regarding
the synoptic pattern by Monday morning, depicting the mid/upper-
level ridge over the southeast CONUS and a deep trough over the
central and western states. As this trough moves east, we can
expect an eventual cold front in West Central TX. Model consensus
currently points to a Monday night frontal passage, with cooler
temperatures expected on Tuesday. Rain chances are a big question
mark for now. Large scale ascent will be on the increase
downstream of this trough, but the quality of moisture return is
uncertain and the cap associated with the EML will need to break
in order for showers and thunderstorms to develop. The ECMWF
parameterization does develop some precipitation across the CWA,
but the GFS keeps the forecast dry for our neck of the woods, with
QPF confined to our east. Given the low confidence in this
scenario, the precip chances were left out of the forecast for
now.

Johnson

&&

.PRELIMINARY POINT TEMPS/POPS...
Abilene  56  79  59  81  59 /   5  10  20  20   5
San Angelo  55  81  57  81  56 /  10  20  20  20   5
Junction  55  82  57  81  55 /   5   5  10  20  10

&&

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

&&

$$

19/25




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