Area Forecast Discussion
Issued by NWS San Angelo, TX

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607
FXUS64 KSJT 211730
AFDSJT

Area Forecast Discussion
National Weather Service San Angelo TX
1230 PM CDT Sat Oct 21 2017

.AVIATION...
/18Z TAFS/

MVFR ceilings will scatter out across the southern terminals by
20-21Z. A cold front will move south across the area late this
evening and overnight. Some convection is expected to develop
along and ahead of the front tonight but extent of coverage is
uncertain at this time and will only mention mainly VCTS across
the terminals for now. A little more confidence for the KABI
terminal and have a 1 hour TEMPO group for 4SM TSRA between
02-03Z. South winds will gust to around 20 to 30 knots across the
terminals this afternoon, subsiding by early evening. Expect FROPA
across the northern terminals between 04Z and 06Z and between 08Z
and 09Z across the southern terminals.

&&

PREV DISCUSSION... /issued 431 AM CDT Sat Oct 21 2017/

SHORT TERM...
(Today and Tonight)

Severe Storms Possible This evening...

An upper level trough and associated cold front will be the main
focus in the short term, with the potential for some severe storms
later this evening.

A progressive upper level trough will move east from the Rockies and
into the Plains this afternoon and evening. Associated cold front is
still on track to enter the Big Country early this evening, then
surge south across the forecast area, exiting far southern sections
after midnight. Ahead of the front, a dryline will become
established across far western counties this afternoon. Could see
some isolated convection develop ahead of the dryline over western
portions of the Big Country, south across western portions of the
Concho Valley and into Crockett county late this afternoon. However,
confidence remains low concerning convective initiation along the
dryline and will keep POPs at 20 percent for now. Storms that do
develop will have the potential to become severe, with the main
hazard being large hail.

A better chance for storms will be this evening ahead of the cold
front as it moves south across the area. The most favored area for
severe storms this evening will be along and north of Interstate 20,
where strong shear and moderate instability will exist ahead of the
front. The main hazards will be large hail and damaging winds but an
isolated tornado cannot be ruled out. Severe storms should be more
isolated south of the Big Country ahead of the front later tonight,
with the main hazard being damaging winds and hail.

Temperatures will be quite warm ahead of the front today, with
afternoon highs in the mid and upper 80s. Lows tonight will range
from the lower 50s across northwest counties, to the upper 50s over
far southeast counties.

LONG TERM...
(Sunday through Friday)

In the wake of the cold frontal passage tonight, our area will have
cooler and much drier conditions on Sunday, with sunny skies.
Somewhat breezy north winds will decrease by mid-to-late afternoon.
Highs on Sunday will be in the lower to mid 70s.

Good radiational cooling is expected Sunday night with clear skies,
dry air and light winds as surface high pressure shifts southeast
across our area. Overnight lows will be mostly in the 40s. The
coolest readings (near 40) will be in the low-lying areas and along
the river valleys of the central and southern parts of our area.
Would not be surprised to have upper 30s lows at a few locations.
Going with mid to upper 40s for lows across the Big Country, where
southwest winds will develop late.

Dry conditions are indicated across our area for at least Monday
through Thursday of next week, with mostly clear skies expected.
With southwest to west winds on Monday, temperatures will rebound
into the lower 80s for highs, after a chilly start to the day. A
cold frontal passage is progged on Monday night, associated with an
upper trough deepening over the Midwest. After a cooler day Tuesday,
good radiational cooling is indicated Tuesday night when surface
high pressure is once again forecast to move southeast across our
area. A warming trend follows Wednesday and Thursday, with southwest
winds on Wednesday and increased south-southwest winds on Thursday.
The GFS continues to show a fairly pronounced 850mb thermal ridging
pattern across our northern and western counties Thursday, ahead of
an approaching cold front. Going with highs in the mid to upper 80s
across most of our area, but would not be surprised to see a few
lower 90s. A strong cold frontal passage is progged Thursday night
and early Friday morning, with temperatures much cooler on Friday.

The 00Z GFS and ECMWF differ notably with the pattern late next
week, and this would have implications for rain chances across our
area. In general, the GFS deepens an upper trough over the central
CONUS and is dry for our area. The ECMWF deepens the upper trough
over the Rockies and has a closed low over the Four Corners region
Friday evening. This pattern would support a possibility of elevated
convection in at least parts of our area. For now, the collaborative
approach has slight chance PoPs Friday night for roughly the
southern half of our area.

&&

.PRELIMINARY POINT TEMPS/POPS...
Abilene  86  54  73  46 /  20  50   5   0
San Angelo  88  55  76  44 /  20  40   5   0
Junction  84  58  77  40 /   5  60   5   0
Brownwood  86  56  75  44 /  10  80   5   0
Sweetwater  86  53  73  50 /  20  20   5   0
Ozona       83  55  75  41 /  20  40   0   0

&&

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

$$

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