Area Forecast Discussion
Issued by NWS San Angelo, TX

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FXUS64 KSJT 201118

618 AM CDT SAT SEP 20 2014

/12Z TAFS/

Low clouds have set in at all forecast terminals excluding KJCT
this morning, with ceilings generally between 1,000 and 1,500 ft.
There are a few IFR observations out there, and these may briefly
affect the TAF sites, but the prevailing heights should remain
MVFR. These ceilings are expected to improve to VFR (greater than
3,000 ft) after 18z. Scattered showers and thunderstorms are
anticipated today, so VCSH was appended to all forecasts. After
00z, convective coverage will begin to diminish and shift west,
so no mention of precip was carried past 02z. If any terminals are
affected by heavier rain showers...temporary fluctuations in
visibility/ceiling are certainly possible. However, thunder is not
expected to be all that widespread. Low clouds will be a
possibility again tonight, but confidence is not all that great.




(Today and tonight)

A quick glance at the water vapor loop suggests that the upper-
level anticyclone is building over northern Mexico with a
general easterly flow over West TX. Mid-level winds are a bit more
nebulous, with the remnants of Odile becoming very difficult to
discern. A band of showers developed across the Concho Valley
early this morning, running from Colorado City, to Robert Lee, to
Miles. However, organization was poor and this activity continues
to weaken. Farther west, activity has been more persistent. Based
on radar trends, it appears that there may be an MCV from earlier
convection near Midland. That would make sense given the
precipitation trends on it`s eastern flank. This feature will
weaken as it moves slowly east, but will continue to interact with
a very moist environment.

This morning, the models (including the hi-res runs) focus the
precipitation over the northern half of the CWA. However, by
midday, we should see sufficient heating in the southern half of
the forecast area for scattered diurnal convection to develop.
Even with temperatures only warming into the mid 80s, BUFR
soundings in the San Angelo area show no cap with SBCAPE values
near 1500 J/kg. It still appears that showers will be the
predominant weather type, but thunderstorms are still possible.
Precipitable water values remain between 1.8" and 2.0" across West
Central TX, which is approximately 2 standard deviations above
normal (or in the 95th percentile). The melting level will be
around 15,000 ft AGL, supportive of efficient warm rain processes.
Thus, the threat for locally heavy rainfall will continue. That
said, the heaviest rainfall has been rather localized over the
past few days, and should remain as such, so no Flash Flood Watch
will be issued at this time.

Convection is expected to shift back to the west this evening,
with the best rain chances being west of an Abilene to San
Angelo line. PoPs for tonight are tapered from 60% in the west to
30% in the east. The heavy rainfall threat will continue, but is
expected to shift west in line with the better organized
convection. Slightly drier air is forecast to work into the area
tonight with overnight lows mainly in the upper 60s.

(Sunday through Friday)

Drier air in the mid level works in from the northeast Sunday.
There is still enough moisture to bring isolated to scattered
showers and thunderstorms, however, with the best chance of rain
west of a Sweetwater...San Angelo...Sonora line. A few areas of
locally heavy rainfall are possible west of the line, where the
NAM and GFS indicated precipitable water above 1.5 inches.
Unfortunately a weak cold front, previously in the computer
models, and possible focus for heavy rainfall in West Central
Texas, is not present Sunday.

The GFS and the EC models indicated isolated afternoon convection
next week, as moisture at and below 700 MB remains, along with
weak ridging aloft. Maintained the slight chance of showers and
thunderstorms Monday, but left out the rest of the work week
given low probability of occurrence.


Abilene  84  69  86  68  86 /  60  40  20  10  20
San Angelo  83  69  86  67  87 /  60  40  30   5  20
Junction  85  71  87  68  89 /  50  40  20  10  20





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