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000
FXUS64 KSJT 131115
AFDSJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN ANGELO TX
515 AM CST Fri Dec 13 2013

.AVIATION...
/12Z TAFS/

Patchy low ceilings have been observed this morning but have been
rather transient. Low level dewpoint depressions are a bit larger
than I would like to see for the development of low clouds but
moisture advection and forced ascent will maintain occasional MVFR
conditions through mid/late morning. By midday, scattered rain
showers will decrease from west to east with clearing skies
following a similar trend. Southwest winds will increase to 12-16
kts (sustained) with gusts around 25 kts at times (especially at
KABI, KSJT, and KSWW). Winds will lay down around 00z but are
expected to shift to the northwest after 06z as a cold front moves
south across West Central TX.

Johnson

&&

.PREV DISCUSSION... /ISSUED 405 AM CST FRI DEC 13 2013/

SHORT TERM...(Today and tonight)

A potent upper-level shortwave trough currently centered just east
of Phoenix, AZ will continue to move east today, traversing the
southern Plains late this afternoon and evening. Ahead of this
cyclone, deep-layer warm advection will be coupled with enhanced
mesoscale ascent associated with the left exit region of a 120 kt
jet streak nosing into West TX. This forcing will be strongest
through mid-morning, waning by midday. Low-level dewpoints remain in
the low to mid 30s across the CWA but analysis of the 850mb RAOB
data showed deeper moisture advecting north out of South TX.
Precipitable water at sampling via GPS satellite indicated this
increasing moisture at San Angelo (increasing from 15mm to 25mm over
the past 12 hrs). Radar echoes are coincident with abundant
mid-level moisture and will continue to moisten the column from the
top down through the overnight hours.

As the mid/upper-level trough axis pass, we`ll see a more subsident
regime overspread West Central TX. I expect precipitation to end and
skies to clear from west to east beginning by midday. However, the
eastern zones (think Brownwood and San Saba) likely won`t clear out
until closer to sunset. Rain will be light across West Central TX,
with most areas receiving less than 1/10 of an inch through this
afternoon. Temperatures today will be some of the warmest we`ve seen
since December 4, but we`ll still only top out near normal. Highs
will range from the mid 50s in the east to near 60 degrees to the
west. Tonight, winds will veer to the west as a surface trough moves
across the area. This surface trough will be followed by a cold
front late tonight. This will shift winds to the north afternoon
midnight and bring cooler/drier air back to West Central TX.
Overnight lows will likely be in the low/mid 30s. No precipitation
is expected tonight.

Johnson

LONG TERM...(Saturday into Friday)

..Cooler on Saturday, then a warming trend...

Surface high pressure will continue to build in behind the cold
front Saturday. The origins of the airmass are in the Rocky
Mountains, versus the Canadian/Arctic airmass intrusions the last
couple weeks. Thus, temperatures are not expected to be as cold.
Nevertheless, there will be enough cold advection to keep
temperatures 10 to 12 degrees lower for Saturday. Winds will be
breezy at times.

Saturday night will be another good radiational cooling event as
surface high pressure centers over West Central Texas early Sunday
morning. With a dry atmospheric column and light winds, temperatures
in the mid 20s are expected, with protected low lying areas falling
into the lower 20s.

Warming trend expected through the middle of next week. With a dry
atmosphere and clear skies, there will be a good diurnal temperature
change through the first half of the week. Low level moisture
however will be returning by Thursday, ahead of an upper trough
developing in the Southwest. There does appear to be the potential
for an Arctic front beyond the current forecast, with the EC and GFS
models indicating an Arctic front a week from today (Friday). There
remains a lot of uncertainty however given how far out the forecast
is.

04

&&

.PRELIMINARY POINT TEMPS/POPS...
Abilene  57  32  45  27  58 /  30   0   5   0   5
San Angelo  60  32  50  26  59 /  20   0   5   0   0
Junction  58  36  52  24  60 /  30   0   5   5   5

&&

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

&&

$$

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