Area Forecast Discussion
Issued by NWS San Angelo, TX

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FXUS64 KSJT 011200 AAA
AFDSJT

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE SAN ANGELO TX
600 AM CST Sun Mar 1 2015

.AVIATION...
/12Z TAFS/

LIFR conditions will continue until mid-morning with freezing
drizzle and fog. The longest duration of freezing drizzle is
expected at KABI, up to Noon. Otherwise, patchy drizzle and light
fog will continue this afternoon at KBBD and KJCT. Generally IFR
conditions are expected this afternoon and early evening. Ceilings
may climb to or just above 1000 ft at times this afternoon, at
KSJT and KSOA. A general deterioration of conditions is expected
tonight, with ceilings lowering to or below 500 ft and a
redevelopment of drizzle/freezing drizzle and fog.

19

&&

.PREV DISCUSSION... /ISSUED 428 AM CST Sun Mar 1 2015/

SHORT TERM...
(Today and Tonight)

We have extended the Winter Weather Advisory until Noon today
across the Big Country area (counties along/north of I-20). Have
also adjusted temperatures down today and tonight.

The shallow cold air is wedged in with surface high pressure ridge
extending from eastern Kansas south-southwest into Texas.
Leaning toward the NAM and SREF for temperatures today and
tonight, as the GFS has been trying to scour out the low-level
cold airmass too quickly.

Temperatures have remained nearly steady overnight, with ongoing
freezing drizzle across most of west central Texas, to the north
of an Ozona to Junction line. Temperatures are expected to
slowly climb today, and should be just above freezing by or
shortly after 9 AM across all but the Big Country area. By this
afternoon, expect temperatures finally be above freezing across
the Big Country. Relative to the rest of the area, Crockett County
will have the warmest high temperatures this afternoon, in the
lower to mid 50s.

Drizzle and freezing drizzle will continue this morning, and
isentropic lift with a moist boundary layer supports a
continuation of light drizzle/fog this afternoon across our
northern and eastern counties.

Backdoor cold front will will progress through our area this
evening and tonight. Expect a deterioration of conditions once
again overnight, as the boundary layer moistens and weak
isentropic lift continues. The main concern is with the potential
for freezing drizzle late tonight as temperatures drop to or below
freezing across much of the northern half of our area. A little
light rain or freezing rain is also possible overnight, mainly
across the northeastern part of our area, with the possible
influence of a weak embedded shortwave in the southwest flow
aloft.

19

LONG TERM...
(Monday through Saturday)

This abnormally cold and damp trend will continue on Monday as
moist, east/northeast low-level winds undercut the strong
southerly flow riding up and over the entrenched cold dome.
Isentropic ascent remains quite strong through Monday evening but
begins to wane by Tuesday morning as winds above the surface veer
to the southwest and west. QPF will remain light as most
precipitation will be in the form of drizzle and light rain.
Early morning temperatures will be near freezing across the Big
Country, necessitating a mention of rain OR freezing rain through
mid-morning. That said, the marginal freezing temperatures should
keep the threat for additional ice accretion rather low. The
abundance of low-clouds and light precipitation will keep max
temps in the 40s Monday afternoon.

Light rain will be possible again on Tuesday, with the best rain
chances generally east of an Abilene-San Angelo line. Warm
advection will be working on this airmass Monday night and
Tuesday, helping to finally break the pesky inversion that has
persisted across the area the past several days. Skies are
forecast to remain mostly cloudy, but with low-level winds
veering to the southwest and 850 mb temps warming to 12-15C,
surface temperatures are expected to jump into the 70s across most
of the area. However, this warm-up will be short-lived as the next
arctic airmass is poised to affect West Central TX by early
Wednesday.

Elevated convective instability is progged to be present along and
ahead of this front. Thus, a chance of showers and thunderstorms
was included for Tuesday night. Based on the projected time of the
cold front`s arrival, temps on Wednesday will likely peak early in
the day, falling into the upper 20s and 30s during the afternoon.
A strong band of mid-level frontogenesis is progged to develop
across the area, juxtaposed with strong dynamic forcing for ascent
associated with the potent shortwave trough moving into west TX.
Point soundings indicate the potential for freezing rain and/or
sleet across the Big Country on Wednesday, shifting south during
the afternoon. Just how far south remains to be seen as these
shallow cold fronts are generally faster and colder than depicted
by the models.

The sounding saturates and cools sufficiently to support snow by
Wednesday night into early Thursday before precipitation comes to
an end and drier air takes over. There is some concern that the
upper-levels dry out before precipitation ends, which could mean a
brief period of freezing drizzle Thursday morning. Given the drier
air advecting into the area in the wake of the cold front, QPF
amounts from the global models look a bit overdone (GFS projects
0.50-1.25" and the ECMWF 0.50-1.00") but we`ll have to wait and
see as precipitable water is forecast to approach 1" (which is
near 2 standard deviations above climo).

Temperatures will remain cool on Thursday with highs in the upper
30s to lower 40s, but a gradual warming trend is expected heading
into the weekend. The forecast is generally dry Friday through
Sunday with afternoon temperatures approaching 60 degrees.
However, a slight chance of showers was included for the extreme
southeast portion of the CWA from Mason to Brownwood on Saturday
as a fast-moving shortwave trough provides a brief chance for
rain showers.

Johnson

&&

.PRELIMINARY POINT TEMPS/POPS...
Abilene  38  30  41  39  71 /  20  30  40  40  20
San Angelo  41  32  46  43  75 /  10  20  30  40  10
Junction  46  38  51  46  77 /  10  20  30  40  20

&&

.SJT WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY until Noon CST today FOR THE FOLLOWING
ZONES: Callahan...Fisher...Haskell...Jones...Nolan...
Shackelford...Taylor...Throckmorton.

WINTER WEATHER ADVISORY until 9 AM CST this morning FOR THE
FOLLOWING ZONES: Brown...Coke...Coleman...Concho...Irion...
Kimble...Mason...McCulloch...Menard...Runnels...San Saba...
Schleicher...Sterling...Tom Green.

&&

$$

99/99/99




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