Area Forecast Discussion
Issued by NWS San Angelo, TX

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FXUS64 KSJT 021121 AAA
AFDSJT

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE SAN ANGELO TX
521 AM CST Mon Mar 2 2015

.AVIATION...
/12Z TAFS/

IFR/LIFR conditions are occurring early this morning with
fog, drizzle and light freezing drizzle, and north-northeast
winds. The drizzle will taper off later this morning with cloud
ceilings climbing a few hundred feet. Indications are for ceilings
to climb above 1000ft into low-end MVFR at most if not all of the
TAF sites, between roughly 20Z and 02Z. A degradation to IFR
ceilings is expected early tonight, as ceilings decrease to
400-700 ft. Wind speeds will stay mostly under 10kt. Winds will
veer to the east this evening, and to the southeast and south
tonight. The chance for showers tonight is low, and not including
at any of the TAF sites at this time.

&&

.PREV DISCUSSION... /ISSUED 340 AM CST Mon Mar 2 2015/

SHORT TERM...
(Today and Tonight)

Temperatures are currently in the lower to mid 30s across west
central Texas with fog, drizzle and light freezing drizzle. Most
of the freezing drizzle has occurred across the Big Country
during the night, and this will continue until mid-morning. We
have a Special Weather Statement to address the possibility of
patchy ice on bridges and overpasses. With marginal freezing
temperatures, however, the threat for additional icing on roads is
low. Isentropic lift will continue today, but boundary layer
moisture will decrease this afternoon. Carrying a mention of
patchy drizzle until Noon. With the possibility of a weak embedded
disturbance moving over the area in southwest flow aloft, have a
slight chance for light rain across much of the area this
afternoon.

Similar to yesterday, favoring the colder NAM with temperatures
today. With surface high pressure ridge extending from the Midwest
southwest into Texas, the low-level cold air is wedged in for
one more day today. Low cloud cover is expected to persist today
and tonight across virtually all of west central Texas, although
some breaks may occur this afternoon and evening in our far
western counties. Highs this afternoon are expected to range from
the upper 30s across the area north of Abilene and Sweetwater, to
the lower 50s in Crockett County south and west of Ozona.

Winds will veer to the east this evening and to the southeast and
south tonight. With low-level warm air advection and the possible
approach of an embedded disturbance aloft, carrying low PoPs for
showers tonight. Little drop-off with temperatures is expected, and
temperatures should hold steady or perhaps rise a bit overnight.

LONG TERM...
(Tuesday through Sunday)

Cue up the roller coaster references for the Tuesday forecast.
Model consensus is that the strong southerly flow that has been
riding over the cold dome, resulting in persist drizzle, finally
scours out this cold airmass. Given the determination of this
airmass, I`ve been looking for a reason to suggest this will not
occur, but even the hi-res models are jumping on board.
Temperatures at 850 mb are progged to increase from 6-8C 00z this
evening to 14-16C by 00z tomorrow. If we are able to mix to 850
mb, surface temperatures will reach the mid 70s. With only partly
sunny conditions anticipated, a conservative approach is
warranted, keeping the max temp closer to the cooler NAM MOS,
which has been the lesser of two evils the past few days. A few
showers will be possible across the eastern portion of the CWA,
but rainfall amounts will remain on the light side.

With yesterday being the first day of meteorological spring, Mother
Nature must have missed the memo. Another arctic cold front is
poised to move across the area early Wednesday morning, with post
frontal temperatures rapidly falling to near the freezing mark. The
faster model solutions seem to be the most prudent given the model
biases associated with shallow arctic air. With that in mind,
temperatures will likely peak in the morning, falling throughout the
day. Large scale ascent moving over the frontal zone will promote
light precipitation areawide Wednesday and Wednesday night. The
strongest forcing will likely be tied to where mid-level
frontogenesis is coincident with the right entrance region of the
upper-level jet streak. However, a faster, strong cold front could
shift this zone of mesoscale ascent south of I-10 before all is said
and done.

Point soundings continue to suggest that freezing rain/drizzle is
likely across the Big Country on Wednesday, mixing with sleet at
times as the column cools. Farther south, we`ll see mainly light
rain, but a few thunderstorms are possible in the vicinity of the
frontal zone. Soundings sufficiently cool and moisten to support
snow Thursday night, but quickly dry out, bringing the threat for
wintry precipitation to an end Thursday morning. As stated
yesterday, there is some concern that the drying aloft could
precede the lift shifting east, adding a freezing drizzle
potential. Will put this concern in my pocket for now, and only
mention snow. Model QPF looks more reasonable than what was shown
yesterday, with generally 0.50" or less (it is noted that the 00z
GFS is higher across the Hill Country where instability is
strongest). This should limit winter precipitation accumulations.
A light glaze of ice is not out of the question, but snow totals
should remain under 1".

Drier air advects into the area Thursday morning, with dewpoints
falling into the teens. The sun should make an appearance on
Thursday, but cool temperatures will prevail with highs in the
neighborhood of 40 degrees. Expect cold temperatures Thursday
night given the dry air and light winds. The only caveat is the
possibility that clouds redevelop. The current forecast lows are
in the low/mid 20s. A warming trend will begin on Friday,
continuing through the weekend. The forecast is dry through
Sunday, but we`ll have to watch the shortwave trough moving out of
Mexico on Saturday. This could require a chance for rain showers
at a later time. Afternoon temperatures will gradually approach 60
degrees by the end of the forecast period with overnight lows in
the 30s.

&&

.PRELIMINARY POINT TEMPS/POPS...
Abilene  40  38  71  36  37 /  20  30  10  40  60
San Angelo  44  43  75  45  46 /  10  30  10  20  60
Junction  47  45  73  48  50 /  10  20  10  30  50

&&

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

$$

Aviation and Short Term: 19
Long Term: Johnson





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