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000
FXUS64 KSJT 070531
AFDSJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN ANGELO TX
1131 PM CST FRI DEC 6 2013

.AVIATION...
Low clouds have eroded across most of West Central TX this evening
in response to the low-level dry air advecting into the area with
the only MVFR ceilings remaining near KOZA. I expect VFR conditions
to prevail at the TAF sites overnight but as winds above the shallow
frontal zone veer to the east and southeast, we`ll see isentropic
ascent increase, resulting in a top down moistening of the column.
These clouds are expected to return by 15z near KJCT and KSOA,
spreading north through early afternoon.

The isentropic ascent should be sufficient to produce at least some
patchy freezing drizzle (possibly in conjunction with sleet) but it
may take a bit of time to moisten the low-levels. Confidence that
freezing drizzle will occur is greatest over the Big Country and
into the Concho Valley. Thus, I have only included FZDZ for KABI and
KSJT with ceilings quickly falling into the low end of the MVFR
category (~1500 ft). Farther south, the lift will be weaker and may
preclude sufficient moistening to realize precipitation at the
surface. Low clouds are expected to persist through the overnight
hours, likely falling into IFR criterion after 00z.  Winds will
remain from the north to northeast at generally 12 kts or less
through the TAF period.

Johnson

&&

.PREV DISCUSSION... /ISSUED 545 PM CST FRI DEC 6 2013/

AVIATION...
Drier air is working its way south across the Big Country this
evening and we`ve seen low clouds beginning to erode in the vicinity
of KABI. I think we`ll hang on to MVFR ceilings here for a bit
longer but overnight we should see generally VFR conditions. A
similar scenario is expected at KSJT but I do not expect VFR
conditions until after midnight. Farther south, low clouds are
expected to persist through the overnight hours. The next wave is
moving across southern AZ at this time. Ahead of this feature, a
prominent mid-level moisture feed is evident on the water vapor loop
and should provide a good deal of high clouds overnight. This may
prevent low clouds from redeveloping as temps fall.

By mid-morning, 850mb winds will veer to the southeast, enhancing
isentropic ascent over West Central TX.  I expect cloud bases to
lower as we moisten from the top down at both KSJT and KABI,
potentially falling back into MVFR category by mid-afternoon. We may
also see some freezing drizzle or a few sleet pellets as this wave
approaches. This may again play havoc with airport operations late
in the TAF period but at this point. I did not include it in the
TAFs being it will likely occur after 18z but it may need to be
included in the next issuance. On a side note, the observation at
KBBD has been missing for the past 16 hours (likely a failure due to
ice). Using the total observation concept, I have issued a TAF but
amendments are not anticipated until the ob has returned.

Johnson

PREV DISCUSSION... /ISSUED 330 PM CST FRI DEC 6 2013/

SHORT TERM...
(Tonight and Tomorrow)

Very COLD conditions to continue across West Central Texas.

Have seen a few breaks in the clouds this afternoon, but its been
tough to clear very much out. Visible satellite shows a few holes,
and quite a bit of ice and snow cover as well. Temperatures have
struggled to climb, still below freezing areawide. Much of the Big
Country along and north of I-20 is still sitting in the mid 20s.

For right now, will lean towards the model data which suggests
clouds will linger and keep at least partly cloudy skies tonight.
With the ice and snow in place, and with it already starting out so
cold, will not argue with the guidance numbers dropping overnight
lows into the single digits across the I-20 corridor north into
Haskell and Throckmorton. Given even a 5 to 10 mph north wind, this
will also translate into wind chill advisory criteria. With the
clouds perhaps not clearing off completely though, did remain with
the "warmer" guidance numbers. In either case, the forecast lows
tonight at both Abilene and San Angelo will threaten record values
for the date.

Saturday forecast still looks in good shape and few changes were
made. Return flow starts as 850 MB winds return out of the
southeast. Not a lot of moisture to work with, but even a little low
level moisture return up and over the shallow bitterly cold air mass
may result in freezing drizzle. Kept the temperatures at or below
freezing as low clouds become solid once again.

CLIMATE...

Record Lows  6th   7th   8th
Abilene       10    15    10
San Angelo    11    21    12

LONG TERM...
(Saturday Night through Friday)

Another very cold morning is forecast on Sunday, with lows in the
teens to lower 20s across most of the area. As surface winds swing
back to the south overnight Saturday, moist air overriding the cold
air at the surface may result in patchy areas of light freezing
drizzle over the eastern and northern half of the forecast area.
During the day on Sunday, downsloping southwest winds and decreasing
clouds ahead of the next cold front will see afternoon highs warm
into the lower 50s over the southwestern counties. highs over the
eastern and northern half of the area will not warm as much, with
afternoon highs in the 40s. These warmer temperatures should allow
any most of the remaining ice/sleet cover over the area to melt.

The next upper level trough will swing across the Northern and
Central Plains on Sunday, pushing the next cold front accompanied by
another surge of arctic air into West Central Texas early Monday
morning.  After warmer morning lows on Monday mostly in the 20s,
afternoon highs on Monday will only warm into the 20s north of
Interstate 20 and into the 30s south of Interstate 20. Expect
another bitterly cold morning on Wednesday as lows remain in the mid
to upper teens. Wednesday afternoon highs will warm in to the upper
40s to the lower 50s.

An upper level low over the Baja on Wednesday will move east over
the forecast area late Thursday bringing a slight chance of rain
over most of the area overnight Thursday.  Will see afternoon highs
on Thursday and Friday in the 50s with morning lows on Friday in the
lower to mid 30s.

&&

.PRELIMINARY POINT TEMPS/POPS...
Abilene  12  19  13  40  21 /  10  10  20  10   5
San Angelo  15  23  17  53  27 /  10  10  10  10   5
Junction  18  30  19  53  27 /  10  10  10  10   5

&&

.SJT WATCHES/WARNINGS/ADVISORIES...
WIND CHILL ADVISORY until Noon CST Saturday FOR THE FOLLOWING
ZONES: Callahan...Fisher...Haskell...Jones...Nolan...
Shackelford...Taylor...Throckmorton.

&&

$$

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