Area Forecast Discussion
Issued by NWS San Angelo, TX
FXUS64 KSJT 181153 AAA
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN ANGELO TX
553 AM CST WED DEC 18 2013
The main Aviation concerns include increasing south winds
today into tonight, and MVFR ceilings with low cloud
South winds will increase today and become gusty by this
afternoon. Expect gusts of 20-25 KT across much of the area.
A decrease in south winds is expected this evening, followed
by an increase overnight with developing low-level jet. The
higher speeds overnight are expected at KABI. Marginal low-
level wind shear could develop overnight at the southern TAF
Low cloud development tonight is expected initially across
the area between Sonora, Brady and Junction. The low cloud
development should rapidly expand north overnight, to north
of the Interstate 20 corridor. Cloud ceilings are expected to
be mostly in the 1-2 kft range, in the MVFR category.
.PREV DISCUSSION... /ISSUED 355 AM CST WED DEC 18 2013/
(Today and Tonight)
A weakening upper level ridge over the southwestern states will
broaden out as it shifts east into Texas today. The flow aloft will
begin to become southwesterly over Texas by early Thursday morning,
as an upper trough dives south along the West Coast. At the surface,
lee side trough will develop along the Texas/New Mexico border today
and remain in place tonight. With increasing surface pressure
gradient across our area, south winds will increase, especially by
this afternoon, and become gusty. With generally clear skies today
and 850 mb temperatures near to slightly above those of yesterday,
leaning toward a near persistence temperature forecast and going
with highs a few degrees above guidance across much of our area.
Low-level moisture will begin to increase today, and to a
considerable extent tonight, as south winds continue. This is
expected to result in rapid development and northward expansion of
low clouds during the night. Increasing cloud cover and higher wind
speeds will keep temperatures mild tonight, with lows in the upper
40s to lower 50s. It has been about 2 weeks since our area has seen
minimum temperatures this warm.
(Thursday through Christmas)
Still looks like widespread rain for Friday and Saturday, then
cooler and dry for Christmas.
Not much has changed with the forecast, and still remained focused
on the chance of rainfall for all of West Central Texas for Friday
and Saturday. Upper level storm system will develop across
California on Thursday as a strong jet dives down the US West Coast.
This system will slide into northern Mexico by Friday. Models start
to generate rainfall as early as Friday evening, as weak shortwave
ahead of the main system begins to interact with increasing low
level moisture return from the Gulf of Mexico. Have increased rain
chances just slightly on Friday afternoon areawide.
At the surface, a cold front will slide south into West Central
Texas Friday morning, and then begin to stall somewhere across the
area south of Interstate 20 during the day. This front is not as
cold as we were originally thinking several days ago, but with cloud
cover in place, will still have a dramatic difference on those areas
north of the front. Highs Friday north of the front only in the 40s
Best lift from the system begins late Friday night into Saturday
afternoon, and this is when most of the rain should fall. Abundant
low level moisture with PWAT`s of an inch or more, well above normal
for this time of year, the lift from the system, and with the cold
front in the area, all combining to set the stage for widespread
rainfall. Given the lift and with mid level lapse rates sufficient,
at least isolated thunder looks likely as well.
Models still have some slight differences with the main upper level
storm system, with the GFS still a little weaker and faster than the
ECMWF. In either case, as the system moves southwest to northeast
from the Permian Basin to central Oklahoma Saturday night and early
Sunday, the deformation zone on the back side will skirt the area
mainly north of I-20. Still can not rule out a brief changeover from
rain to snow across a small area that includes Haskell and
Throckmorton, and will continue the mention of snow in the forecast.
Rest of the forecast looks dry. Several cold fronts will move
through the area, first on Sunday as the system passes and a second
for Christmas Day. This will keep temperatures at or a little below
.PRELIMINARY POINT TEMPS/POPS...
Abilene 70 53 72 40 52 / 0 0 0 10 20
San Angelo 72 50 72 45 65 / 0 0 0 5 20
Junction 72 49 69 49 71 / 0 0 5 10 20