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000
FXUS64 KSJT 231720
AFDSJT

Area Forecast Discussion
National Weather Service San Angelo TX
1220 PM CDT Wed Aug 23 2017

.AVIATION...
/18Z TAFS/

A weak cold front will continue to move south across the area
this afternoon. Scattered showers and thunderstorms will be
possible across all terminals this afternoon and early evening and
have included VCTS at all terminals with this TAF package. The
stronger thunderstorms have the potential to briefly reduce
visibilities to IFR conditions for a short duration. Otherwise,
expect VFR conditions across the terminals for the next 24hrs.
Early morning low clouds could bring in a few hours of MVFR
conditions to the KABI terminal between 12-14z. Winds will be
light out of the northeast between 3-6 knots before going calm
during the overnight hours.


&&

.PREV DISCUSSION... /issued 657 AM CDT Wed Aug 23 2017/

AVIATION...
/12Z TAFS/

Low cloud cover has developed across the northern third of our
area, with ceilings around 1000 ft at KABI. Expect low cloud
cover to persist into mid-morning at KABI, with MVFR (and possible
intervals of IFR) ceilings prior to 15Z. Scattered showers and
thunderstorms are expected today and into this evening. With
uncertainty in the specific timing and placement of convection,
however, going with vicinity groups at our TAF sites at this time.
Winds will be from the north-northeast at KABI today, veering to
the northeast tonight. At KSJT and KBBD, light winds are expected
to become northeast this afternoon. For our southern terminals,
light winds today should become northeast or east-northeast by this
evening.

PREV DISCUSSION... /issued 438 AM CDT Wed Aug 23 2017/

SHORT TERM...
(Today and Tonight)

Showers and isolated thunderstorms moved southeast across much of
west central Texas during the night, but only a few light rain
showers remain as of 4 AM. A Mesoscale Convective Vortex (MCV) was
apparent in radar imagery just after Midnight between San Angelo and
Sweetwater, and was moving slowly to the southeast. The outflow
boundary from the convection moved into the far southern part of our
area, and was near the I-10 corridor early this morning.

The upper high, centered near El Paso, will continue to weaken today
and tonight, and our area will be under weak northerly flow aloft on
its eastern periphery. The weak cold front, just south of Wichita
Falls and Childress, is expected to sag south across the northern
half of our area today. This front will become more diffuse during
the next 24 hours.

With ample moisture and weak instability today, scattered showers
and thunderstorms are expected across west central Texas. The models
differ with QPF placement and with the progress of the
aforementioned weak frontal boundary. Could have some enhanced
development near the residual outflow boundary in our far southern
counties, along the weak cold front, and in association with the
aforementioned MCV. At this time, we are carrying chance PoPs (40-50
percent) across our area, with the anticipated main time frame
during the afternoon and evening hours. With precipitable water
values in the range of 1.6 to 2 inches, locally heavy rainfall is a
good possibility with the convection.

With increased cloud cover and rain chances, temperatures will not
be as warm today. Highs are expected to be in the mid to upper 80s
across most of the northern half of our area, and in the lower 90s
across some of the southern half. Lows tonight are expected to be
in the upper 60s to lower 70s.

19

LONG TERM...
(Wednesday through next Tuesday)

Scattered afternoon and early evening showers and thunderstorms
are possible Thursday through Saturday. West Central Texas will
remain beneath an upper level col. A col is when there are upper
lows to the north and south and upper highs to the east and west
of your location. By Saturday, the col begins to shift into
northeast Texas as the upper level ridge builds across the Four
Corners. This upper ridge will allow stronger upper level
northerly flow to develop across the region. If Harvey continues
to remain well off to the east, this will result in a drier and
subsident airmass across the area by Monday of next week.

Models show Instability associated with daytime heating and
adequate low level moisture, resulting in low CAPE Values at
around 1000 J/KG or less with no capping inversion for Thursday
through Saturday. This instability should enable scattered
thunderstorms to develop along the diffuse front and outflow
boundaries during the early afternoon and dissipate by the early
evening hours each day. With plenty of cloud cover and light east
to northeast winds, afternoon highs should only climb into the mid
to upper 80s Thursday through Saturday. Also, Tropical
Disturbance Harvey will provide a little extra low level moisture
during this period from the east and southeast.

As the low pressure moves east and northeast of our area, look for
decreasing chances of rain and a north breeze Sunday through next
Tuesday. Afternoon highs mostly in the mid and upper 80s to near
90 will also persist.

26

&&

.PRELIMINARY POINT TEMPS/POPS...
Abilene  70  87  69  85 /  30  40  30  40
San Angelo  70  88  70  87 /  30  30  30  40
Junction  71  89  71  88 /  30  40  30  40
Brownwood  70  87  69  86 /  40  40  30  40
Sweetwater  70  85  69  85 /  30  30  30  40
Ozona       71  88  70  87 /  30  30  30  40

&&

.SJT WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

99/99/40