Area Forecast Discussion
Issued by NWS San Angelo, TX

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000
FXUS64 KSJT 191749
AFDSJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN ANGELO TX
1149 AM CST Fri Dec 19 2014

.AVIATION...
/18Z TAFS/

Look for challenging flight weather conditions for much of the
next 24 hours. Conditions will likely improve to VFR this
afternoon; nevertheless, stratus will redevelop this evening. The
NAM and GFS return conditions to IFR by 12Z at all but the Abilene
terminal. However, confidence for IFR conditions returning isn`t
high; rather, MVFR beginning at 02Z looks best.

Huber

&&

.PREV DISCUSSION... /ISSUED 743 AM CST Fri Dec 19 2014/

DISCUSSION...
Have updated the grids to reflect current trends in radar and
satellite imagery. Lift associated with the upper level low
continues to move northeast away from our CWA, and dry air aloft
also continues to advect in from the southwest over the area,
pointing toward precipitation ending across the area for the most
part. Will keep a slight chance of showers for eastern areas
through the rest of the this morning, as spotty showers will still
be possible, generally east of a Haskell, to Abilene, to Junction
line. Have removed all mention of precipitation for the afternoon.
Updated text products will be out soon. 20

PREV DISCUSSION... /ISSUED 547 AM CST Fri Dec 19 2014/

AVIATION...
/12Z TAFS/

Initially poor conditions should gradually improve throughout the
day. IFR to LIFR conditions, mainly due to low CIGS, are prevalent
across the area this morning. Showers and isolated thunderstorms
are moving out of the area, and are likely to end for the most
part before noon today. However, behind a cold front today, low
clouds are expected to persist at least into the early afternoon
hours, while gradually lifting to MVFR. Have kept a brief period
of VFR conditions in the TAFs for this afternoon and early
evening. With the cold air mass still in place tonight, we could
see these low clouds redevelop after 00Z, so have brought MVFR
CIGS back into the forecast after 00Z tonight at all sites. Winds
will remain generally northeast today, while slowly veering to the
east or southeast tonight. 20

PREV DISCUSSION... /ISSUED 443 AM CST FRI DEC 19 2014/

SHORT TERM...
(Today and Tonight)

Scattered showers and isolated embedded thunderstorms are
currently affecting areas mainly east of an Abilene to San Angelo
to Junction line. A cold front is making progress southward
resulting in cooler/drier air and northeast winds of around 10
mph. The cold front as of 3 AM was moving through the I-10
corridor area. The upper level trough/low bringing the large scale
lift into the area was centered near the TX/NM border northwest of
Lubbock, with much drier air rotating around the southern end of
the cyclonic flow into our forecast area. This trough will
continue moving east/northeast today. The drier air is showing its
effects in our southwestern counties already where precipitation
looks to be over. With the best lift/moisture moving northeast
today, have adjusted PoPs downward after 12Z this morning,
especially for our southwestern counties. We may see lingering
scattered activity this morning generally north and east of a
Sterling City to Ballinger to Junction line, and then an end to
most of the precipitation after 18Z, and continued dry overnight.

Temperatures will be quite a bit cooler today with upper 40s
expected along and north of the I-20 corridor, ranging to the mid
50s along the I-10 highway. Lows tonight will drop into the lower
40s, with some low lying areas and river valleys dropping into the
30s. Do not expect to see freezing temperatures as dewpoint values
are expected to range from the upper 30s to lower 40s.

20

LONG TERM...
(Saturday through Christmas Day)

A shortwave upper trough will move east across the southwestern
states on Saturday, and across west central Texas on Sunday morning.
Only some cloud cover is expected in our area with no rainfall from
this weak system. Southeast winds on Saturday will veer to the
south Saturday night, and to the southwest on Sunday as a surface
trough enters the area. With more sunshine, temperatures will be
a few degrees warmer on Sunday.

An upper trough will deepen over the Plains and Midwest on Monday,
with a closed low developing over southeastern South Dakota. The
GFS and ECMWF differ in handling of this system during the week
across the eastern half of the U.S. With the associated cold
front, the GFS is a little stronger and brings the front south
across our area a little sooner than the ECMWF. Timing of the
front could curtail the warmup Monday in our far northern
counties. Looks warm ahead of the front for our central and
southern counties. Currently carrying highs in the upper 60s/
around 70 degrees, but these highs may need to be increased if
subsequent models show increased 850 mb temperatures with low-
level westerly flow and downsloping effects.

The 00Z models indicate a potential for some light rain to develop
in our northern counties and toward the Red River Monday night,
as a disturbance moves into the base of the aforementioned
deepening upper trough. Holding off with any mentionable PoPs for
now, and will see if subsequent models are consistent with this
setup.

Should have increased/gusty north winds following the cold frontal
passage and continuing into the day Tuesday. Temperatures will be
cooler, but sunshine during the day will help to partially offset the
cold air advection. With the surface ridge axis progged to shift into
our area, lows Tuesday night are expected to be in the 30s with
better radiational cooling.

Dry and warmer conditions are indicated for Wednesday and Thursday.
A return to above normal temperatures is expected, especially on
Christmas Day with south-southwest low-level flow and 850 mb
thermal ridging.

19

&&

.PRELIMINARY POINT TEMPS/POPS...
Abilene  48  35  55  40  58 /  10   5   5   5  10
San Angelo  54  38  58  40  61 /  10   5   5   5   5
Junction  56  38  57  40  59 /  10   5   5   5  10

&&

.SJT WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$






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