Area Forecast Discussion
Issued by NWS San Angelo, TX

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FXUS64 KSJT 220456
AFDSJT

Area Forecast Discussion
National Weather Service San Angelo TX
1156 PM CDT Thu Sep 21 2017


.AVIATION...
/06Z TAFS/

Early morning MVFR and briefly IFR flying conditions are expected
at Junction and Sonora. Elsewhere morning clouds will cause or be
close to MVFR flying conditions.

The trend is toward more cloud cover across the forecast area as
an upper level trough moves close to the area from the west. The
NAM is more aggressive with bringing in low clouds, while the GFS
keeps skies mostly clear. We should see a trend toward increasing
clouds in the GFS in the next forecast run. Current TAFS reflect
the NAM model solution.

A vigorous upper level trough currently over California and
Nevada will move east toward the forecast area. As it does so it
will gradually draw moist air from the Gulf of Mexico
northwestward into the forecast area. This along with lift along
the east side of that trough will result in morning low clouds,
some will persist through the day. Cloud cover will be most
extensive at Junction and Sonora but will work northward and
become more extensive by early next week across the entire
forecast area along with an increasing chance for rain.

22
&&

.PREV DISCUSSION... /issued 620 PM CDT Thu Sep 21 2017/

AVIATION...
/00Z TAFS/

As an upper level trough approaches from the west, morning low
clouds are expected with overcast conditions and MVFR ceilings.
Brief morning IFR ceilings may prevail at Sonora and Junction.
By afternoon partly cloudy to broken cloud cover will prevail with
mostly VFR flying conditions.

22

PREV DISCUSSION... /issued 246 PM CDT Thu Sep 21 2017/

SHORT TERM...
(This Afternoon and Tonight)
.Isolated strong to severe storms possible...

One more hot day across the region today. An area of low pressure
over north central Wyoming will keep the region under the influence
of strong warm air advection (WAA). The 850mb thermal ridge has
moved slightly west, but with temperatures running in the 24-25
degree Celsius range, surface temperatures will once again climb
into the upper 90s. With a high pressure area off to our east and
low pressure to our northwest, a tightening surface pressure
gradient is producing gusty winds this afternoon. Winds will
continue in the 10 to 15 MPH range with gusts up to 25 MPH.

Scattered cumulus are developing from west central Texas into the
Permian Basin, with thunderstorms ongoing in the Davis Mountains
area. Isolated showers and thunderstorms are possible across the
western portions of the CWA this afternoon and evening. With a warm,
moist airmass in place, CAPE values will climb to between 2500-3000
J/kg. Upper level dynamics are still rather weak so organized severe
is not expected, however, a marginal risk for severe is possible
mainly across the northern Big Country, south into the western
Concho Valley and northern Edwards Plateau. The stronger storms will
be capable of producing strong downburst winds in excess of 58 MPH.
Shower and thunderstorm activity will diminish quickly after sunset.

(Friday)

An upper level ridge will develop over the area as an area of low
pressure to our west becomes more defined. The strong 500mb trough
will slowly begin to move east throughout the day on Friday. Cloud
coverage will begin to increase starting Friday evening signaling
the approach of our next weather system. This feature will bring a
change in the weather across the area starting late this weekend. In
the meantime, we will remain under southeast low level flow allowing
for temperatures to remain in the 90s with warm overnight lows in
the low to mid 70s.

LONG TERM...
(Friday night through Thursday)

Generally quiet weather conditions are expected this weekend as an
upper level ridge remains across the Midwest while a large upper
level trough continues across the western CONUS. Generally dry
conditions are expected, with any convection remaining across far
West Texas, closer to the aforementioned upper level trough. A few
storms may approach our western counties, especially late Sunday
into Sunday night. Highs this weekend will be slightly above
seasonal normals, in the upper 80s to near 90 degrees. Overnight
lows will mainly be in the upper 60s to near 70 degrees.

The aforementioned upper level trough will approach West Central
during the first half of next week. As Pacific moisture streams
north and east, ahead of this feature, showers and thunderstorms are
forecast to first develop across West Texas Sunday night into Monday
morning, then spread across much of West Central Texas Monday into
Wednesday. Heavy rainfall will be possible, with storm total amounts
through the middle of next week in the 1 to 3 inch range, although
higher amounts will be possible. The increased cloud cover and
rainfall will result in cooler temperatures, with highs mainly in
the upper 70s to mid 80s. As the upper level trough passes east
of the area, a cold front will move through the region. Relatively
cooler temperatures and dry conditions are expected for the
latter part of the work week.

Daniels

&&

.PRELIMINARY POINT TEMPS/POPS...
Abilene  96  72  91  69 /  10  20   5   5
San Angelo  98  72  93  69 /  10  20  10   5
Junction  95  72  90  69 /  10  20  10   5
Brownwood  94  71  91  68 /  10  10  10   5
Sweetwater  95  72  91  69 /  20  20   5   5
Ozona       94  72  89  69 /  10  20  10   5

&&

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

$$

99/99/99



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