Area Forecast Discussion
Issued by NWS San Angelo, TX

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000
FXUS64 KSJT 281119
AFDSJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN ANGELO TX
619 AM CDT Thu May 28 2015

.AVIATION...
/12Z TAFS/
Few CIGs at MVFR this morning but the remaining TAF sites are VFR.
Could see MVFR CIGs develop between now and 15Z. Should see
improvement to VFR shortly after 15Z. Strong to severe
thunderstorms anticipated for today and tonight that should impact
most TAF sites. Strong winds, large hail and low visibilities in
heay rain could impact all TAF sites tonight. A flash flood watch
is also in effect from 5 PM this afternoon through 7 AM Friday.

&&

.PREV DISCUSSION... /ISSUED 440 AM CDT Thu May 28 2015/

SHORT TERM...
(Today and Tonight)

Expect better coverage of severe thunderstorms and the potential for
locally heavy rainfall today.

A cold pool or outflow boundary associated with an MCS moving east
across OK/N TX can be seen moving into Haskell and Throckmorton
Counties with convection developing immediately behind it.  A few
storms could develop in that region this morning and produce locally
heavy rainfall.

As a large upper level shortwave trough over New Mexico
approaches WC TX today, look for increasing lift from west to east
across the region as the upper flow becomes more divergent at 300
millibars. Storms should develop along old outflow boundaries and
a sfc trough/dry line across the Trans Pecos later this morning
into the afternoon since the capping inversion is weak. Latest
PWATs are forecast to be around 1.7 inches, ML CAPE values in
excess of 3000 j/kg and 0 to 6 km shear will be low. The main
threats will be large hail and damaging winds. Can`t rule out an
isolated tornado especially along the old outflow boundary across
the north.

As storms form along the Trans Pecos dryline this morning, this
cluster of thunderstorms should grow upscale into an MCS by late
afternoon. A strengthening low level jet through the evening,
good upper level divergence, cold pool, and decent PWAT values,
should sustain the MCS as it moves east and southeast later this
evening.  For this reason and in collaboration with neighboring
offices, plan to issue a flash flood watch for a large part of West
Central Texas.

26

LONG TERM...
(Friday through Wednesday)

The shortwave trough will move east of our area on Friday, and by
afternoon expect the associated showers and thunderstorms to be east
of our area. Some decrease in cloud cover from the west should allow
temperatures to climb into the mid to upper 80s for highs.

With the approach of a cold front from the north, showers and
thunderstorms are expected to develop south into the Big Country by
late Friday night. With the flow aloft becoming northwesterly, this
precipitation may be augmented by an embedded shortwave dropping
southeast into northwest Texas. Numerous showers and thunderstorms
are expected across a large part of west central Texas on Saturday,
as the front continues to push south. Although a few strong or
marginally severe storms will be possible, the main concern is with
the potential for heavy rainfall, with precipitable water values
forecast to be between 1.3 and 1.6 inches.

The cold front is expected to move south of our area early Saturday
night, with rain chances dropping off from the north overnight. On
Sunday, an upper level ridge will build over the Arizona/New Mexico
border, while an upper trough develops over east Texas. With
northerly flow aloft over our area along with some instability and
lack of a cap, cannot rule out the possibility of isolated to
scattered showers and thunderstorms, mainly across the southern half
of our area.

For Monday and Tuesday, the forecast is somewhat problematic
regarding rain chances, with some differences in the 00Z GFS and
ECMWF. Both models show an upper ridge to our west over New Mexico.
To our east, the GFS has an upper low drifting south across the
western half of Arkansas, while the ECMWF has an upper trough over
the lower Mississippi Valley with a closed low developing just
southwest of Memphis. The ECMWF has a dry scenario for our area the
aforementioned upper ridge being the main influence.  The GFS
indicates a potential for shower/thunderstorm development across
parts of our area, with northerly flow aloft. For now, going with
low PoPs for showers and thunderstorms across the southeast part of
our area (southeast of a Sonora-Brownwood line) on Monday.

19

&&

.PRELIMINARY POINT TEMPS/POPS...
Abilene  84  66  85  67  80 /  60  70  30  50  50
San Angelo  85  67  88  68  84 /  60  70  30  30  50
Junction  85  67  86  68  85 /  40  60  30  20  50

&&

.SJT WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH from 5 PM CDT this afternoon through Friday
morning FOR THE FOLLOWING ZONES: Brown...Callahan...Coleman...
Concho...Crockett...Haskell...Irion...Jones...Kimble...Mason...
McCulloch...Menard...Runnels...San Saba...Schleicher...
Shackelford...Sutton...Taylor...Throckmorton...Tom Green.

&&

$$

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