Area Forecast Discussion
Issued by NWS San Angelo, TX

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FXUS64 KSJT 261750

Area Forecast Discussion
National Weather Service SAN ANGELO TX
1150 AM CST THU NOV 26 2015

/18Z TAFS/

Cigs were mostly MVFR at 18Z. Mostly concerned with the potential
for isolated to scattered thunderstorms this afternoon. The
strongest storms could approach severe limits and produce wind
gusts in excess of 50kts. Inserted the mention of Thunderstorms
with CB for this afternoon. Otherwise, as front moves into the
area tonight, look for IFR Cigs and possibly Vis. The chance of
thunderstorms will continue with the frontal passage overnight
into tomorrow morning.


.PREV DISCUSSION... /issued 525 AM CST THU NOV 26 2015/

/12Z TAFS/

MVFR ceilings expected through the morning...with conditions
deteriorating to IFR this evening and overnight. Rain showers and
fog may reduce visibility at times, especially after sunset this
evening. A strong cold front will move through the area toward the
end of the TAF period...reaching KABI around 8-9Z and KSJT near
12Z. Strong north wind and continued rain and low visibilities
expected behind the front.


PREV DISCUSSION... /issued 444 AM CST THU NOV 26 2015/

(Today and Tonight)

.Two significant weather concerns for late in the short term:
Heavy rain potential for the northeastern counties, and an Arctic
front with significantly cold temperatures by Friday morning...

Strong upper low continues to dive southeast from Northern California
toward Nevada early this morning. A series of shortwave troughs
ahead of the upper low will impact West Central Texas over the next
24 hours.  We are starting to already see light showers developing
across southwest counties as a weak shortwave trough heads into west
Texas this morning. Today should be mild with highs in the 70s and
scattered light rain showers with low QPF amounts.

However...a major change is expected tonight as a strong Arctic cold
front dives south across the area...and precipitation
increases along and behind the front. Expect the front to reach
Haskell and Fisher Counties by midnight tonight, reaching the
Concho Valley and San Angelo by 6 am Friday morning. Heavy
rainfall is possible along and ahead of the front...with rainfall
amounts near an inch possible over eastern counties. In
addition...temperatures will rapidly fall behind the front down
into the mid to upper 30s, especially along and north of I-20,
with gusty winds of 20 to 25mph.

(Friday through next Wednesday)

.Periods of heavy rain through the weekend, with freezing
temperatures and possible ice on elevated objects (trees and
powerlines) over the Big Country by Saturday morning...

The models remain consistent in their overall solutions through the
next several days. Early this morning, Hurricane Sandra has
intensified to a category 4 storm south of Baja California. Mid
and upper-level moisture from the tropical system is already
heading north towards Texas, and this will add to our rainfall
chances. By sunrise Friday morning, a cold front will be pushing
south through the Concho Valley and Heartland, reaching Interstate
10 a few hours later. Strong convergence along the front and a
moisture-laden airmass (precipitable water values above 1.5
inches) will lead to shower and isolated thunderstorm development
along/ahead of it. Farther north, the 850mb front will slowly work
its way into the forecast area Friday afternoon, and meander
across the area through the weekend. This will be key to where
the heavy rainfall develops, as the remnants of Sandra approach
and embedded vorticity maxima crossing the region in the upper
flow interact with the moisture/front, leading to rainfall
becoming more widespread/ increasing in intensity.

As far as any wintry precipitation is concerned, it still looks like
rain will be the predominant precipitation type. The numerical
guidance continues to show temperatures right near the freezing mark
(31 to 32 degrees) early Saturday morning across all of the Big
Country, and the northern portions of Sterling/Coke counties.
However, warm ground temperatures and a latent heat release from the
heavier precipitation should mitigate any potential for ice
accumulation on area streets. Some elevated objects
(trees/powerlines) may cool sufficiently for accumulations to
develop. For now, we`ve maintained rain as the predominant
precipitation type, but this will be reevaluated each model run to
see if guidance trends colder. Overall it looks like a general 2 to
4 inches of rainfall will occur before everything is said and done
Sunday evening.

Things get interesting once again by the middle of next week. The
GFS/ECMWF disagree on how the upper air pattern will develop during
this time, as the GFS shows a jet streak crossing West Central Texas
in a northwest flow aloft, while the ECMWF develops a closed mid-
level low over northwest Mexico. Both models do indicate
precipitation developing across the forecast area. Given this is
several days out and a recent change in the model data, no
precipitation was included in the forecast at this time.


Abilene  71  40  42  32 /  60  90  90  80
San Angelo  74  46  62  33 /  50  60  90  80
Junction  74  65  69  39 /  60  60  90  80


.SJT Watches/Warnings/Advisories...


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