Area Forecast Discussion
Issued by NWS San Angelo, TX

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FXUS64 KSJT 010515

1115 PM CST SAT JAN 31 2015

/06Z TAFS/

Most West Central TX forecast terminals are reporting MVFR
ceilings as of 05z, but conditions should deteriorate overnight
with most areas dropping into IFR (with ceilings under 1000 ft).
Scattered showers will affect KSJT, KABI, and KSOA early this
morning, but confidence is too low to mention elsewhere.
Otherwise, expect patchy fog/drizzle to restrict visibilities at
times. Winds will veer to the southwest late tonight, shifting to
the north as a cold front moves across the area during the late
morning and early afternoon hours. Winds will be gusty through
around 00z, eventually subsiding after sunset. Ceilings will
rapidly improve behind this front with VFR conditions expected
areawide by mid- afternoon.




Updated the grids and zones to go with chance POPS across the
entire area tonight. Also, a few thunderstorms are possible
across the Northern Edwards Plateau.

PREV DISCUSSION... /ISSUED 638 PM CST Sat Jan 31 2015/

/00Z TAFS/

Ceilings remain below 1500 ft across most of West Central TX, with
many forecast terminals experiencing IFR (or worse) conditions.
The primary rain shield has moved east of the forecast area.
However, isentropic ascent will ramp up overnight, resulting in
lowering ceilings and potential light precipitation, mainly in the
form of drizzle. This will knock cloud bases down to generally
700 ft or lower and should cause prevailing visibilities to drop
to 5 miles or less. Some locations may experience more significant
reductions in visibility. Expect poor flight conditions overnight
but winds will veer to the southwest overnight ahead of a cold
front. This front will move through the Big Country mid/late
morning, bringing drier air into the area and eroding the low
clouds from north to south throughout the day. Gusty north winds
will prevail in the wake of this front.


(Tonight and Sunday )

Light rain was moving north of I-20, and east of an  Abilene...
Brady...Mason line at 3 PM. An upper low was west of El Paso,
moving slowly southeast.

Rain was pushing east and ending of West Central, faster than the
models indicated. Indeed at the current pace, nearly all the
present rain at 3 PM will be east or north of West Central Texas
by 6 PM. Kept a chance of showers going overnight, however, with
the El Paso low sending weak disturbances eastward. Additional
rainfall amounts will be light...ranging from a trace to a few
hundredths inch. The NAM and EC models bring isolated to scattered
light showers over West Central Texas tonight. The GFS model`s
convective algorithm is dry. The short range HRRR model brings in
scattered showers, mainly over Crockett county, the Concho Valley
and areas southward. Timing was between 9 PM and 4 AM. This may
actually be the best model as it seems to latched on an area of
lift in the water vapor loop south of El Paso.

A cold front will move through West Central Texas Sunday bringing
gusty north winds by noon. This clear low level moisture and
clouds. Sunshine in the afternoon should allow afternoon highs to
be a 2-4 degrees warmer than today`s, despite cold air advection.

(Sunday night through next Saturday)

Warmer weather will make a return to West Central Texas for the
first half of the week. An area of high pressure centered over the
region on Monday, will slide off to our east by mid-week. A
thermal ridge at 850 mb will expand east over the area, allowing
high temperatures to climb from the mid 50s on Monday, to the mid
60s by Wednesday. A weak cold front approaching the area from the
north Wednesday night, will wash out near Interstate 10 during the
day Thursday, bringing cooler/drier air to the region. However,
this will be short-lived, as a lee trough develops to our west on
Friday. With a return flow developing, warmer temperatures and
increasing moisture are expected.

Precipitation chances may also increase for the southern half of
the forecast area. An upper-level disturbance currently located
over Baja California, is expected to pass by to our southeast
Tuesday night/Wednesday morning. This system may bring a chance of
rain to the region, mainly south of a line from San Angelo to
Brownwood. This afternoon`s numerical models have once again
shifted the track of the disturbance farther south and east,
reducing forecast confidence. However, the models have been flip-
flopping on the track for the last few model runs, and considering
the system is still largely in a data-void region, this will
likely continue through the next 48 hours. By then, the system
will enter an improving observational/upper-air network, which may
result in improved model continuity. Given the concerns mentioned
above, only minimal changes were made to the rainfall forecast for
the middle of the week.


Abilene  49  51  24  51  36 /  40  10   5   5   5
San Angelo  51  60  27  54  36 /  30  10   5   5   5
Junction  52  64  30  55  34 /  40  20   5   5   5





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