Area Forecast Discussion
Issued by NWS San Angelo, TX

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FXUS64 KSJT 202123
AFDSJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN ANGELO TX
323 PM CST Sat Dec 20 2014

.SHORT TERM...
(Tonight and Sunday)

Cloud cover has been slow to erode this afternoon, similar to what
we saw yesterday. Expect more of the same overnight, with stratus
expanding with most areas overcast by morning. Areas of fog will be
possible across mainly our southern and western counties, where
winds will remain lightest and some breaks in the clouds are
expected. The expected cloud cover will help to keep overnight lows
unseasonably warm, generally in the upper 30s to lower 40s.

Overcast skies are forecast across most of West Central Texas to
begin the day Sunday, but winds will become southwest at 8 to 12 mph
by late morning, ushering in drier air. The dry air intrusion will
help to erode cloud cover across most of the area by late morning or
early afternoon. Highs on Sunday will be above seasonal normals,
generally in the lower to mid 60s.

.LONG TERM...
(Sunday night through Saturday)

Rain chances will return during the first half of the work week.
Models have trended stronger with a Central Plains trough that is
expected to develop during the first half of the week. This is
likely due to better sampling of a very energetic jet stream that is
currently entering the Pacific Northwest. This jet stream was over
the Sea of Okhotsk (northeast of Japan) a few days ago, when it had
a 200+ knot jet stream associated with it. The current upper air
observations show it has weakened to near 150 knots, which is still
pretty respectable for this time of year. As such, the trend in the
model forecasts is for a sharper/deeper trough to develop across the
Central Plains, with a strong mid-level low developing near Iowa,
and a series of vorticity maximums rotating around this mid-level
low.

The first such disturbance will dive southeast across the area
Monday night/Tuesday, with a weak surface low forming ahead of the
system Monday evening across North Texas, sending a weak cold front
south across the area. The frontal timing moved ahead a few hours
compared to the overnight model runs, and this is likely due to the
aforementioned sampling concerns and stronger development that`s
forecast in the data. A down-sloping west to southwest surface wind
will develop ahead of this front. This, along with compressional
heating, and 850 mb temperatures in the 14-17 degree Celsius range,
will allow afternoon highs to climb into the lower to mid 70s across
most of the area. As the vorticity maximum approaches the area,
showers are expected to develop. Given the trend in the data for a
stronger/farther south track, POPs were bumped up to chance category
for areas along/north of Interstate 20, with slight chance POPs
extended farther south into the Concho valley and Heartland.

For Christmas Eve and beyond, the first trough will have departed
the area, with another trough developing to our west. Similar to the
first system, southwest flow aloft will develop over West Central
Texas, with a series of additional vorticity maximums passing by to
our north. The second trough will be more progressive/broad,
resulting in little if any chance for rainfall for the Christmas
Eve/Day. Another weak cold frontal passage is also likely for
Friday. Compressional heating looks to be less of a concern ahead of
the front with this front. However, a favorable wind pattern for
warming via down-sloping, and similar 850 temperatures argue for
highs possible breaching the 70 degree mark. For now, we`ve keep
afternoon highs on Thursday in the upper 60s range, but this may
need to be increased in alter forecasts in a faster frontal timing
is seen.

&&

.PRELIMINARY POINT TEMPS/POPS...
Abilene  41  62  45  72  42 /   5   0   5   5  20
San Angelo  43  64  44  76  42 /   5   0   5   5  20
Junction  41  62  43  74  42 /   5   5   5   5  10

&&

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

$$

Daniels/Doll





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