Area Forecast Discussion
Issued by NWS San Angelo, TX

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FXUS64 KSJT 251738

Area Forecast Discussion
National Weather Service SAN ANGELO TX
1138 AM CST WED NOV 25 2015

/18Z TAFS/

Patchy MVFR ceilings continue across West Central TX, but continue
to slowly improve over time. Most of the area will be VFR this
afternoon, but KSOA is likely to remain MVFR through at least
mid-afternoon. Once the boundary layer begins to cool this
evening, low clouds will return in earnest as isentropic ascent
intensifies. Guidance continues to depict IFR (or worse) ceilings
overnight, but with a strong low-level jet and gusty surface
winds, it will be difficult to realize ceilings that low. In
general, low-end MVFR ceilings (1,000-1,500 ft) are expected, but
may briefly dip below 1,000 ft, mainly along the I-10 corridor.
Patchy drizzle will be possible after midnight with increasing
rain chances during the latter half of the TAF period. Expect
gusty winds overnight, continuing into Thursday.


.PREV DISCUSSION... /issued 634 AM CST WED NOV 25 2015/

/12Z TAFS/
Cigs are MVFR and they should remain that way through much of
today. Winds will be gusty from the south. Expect the development
of IFR Cigs at most TAF sites after 03Z. A few areas of
drizzle/fog producing MVFR visibilities are possible this morning
and again after 03Z.

PREV DISCUSSION... /issued 503 AM CST WED NOV 25 2015/

(Today and Tonight)

A little patchy drizzle along the I-10 Corridor is possible this
morning. Otherwise, expect cloudy, mild and breezy conditions
today with highs in the lower 70s, becoming partly cloudy
briefly this afternoon. A surface low pressure system was located
along the front range of the Rockies, and has formed in response
to increasing upper southwesterly flow extending across much of
the western U.S. into West Central Texas. The southwest flow aloft
will continue today and tonight in advance of an upper low diving
south across California.

Meanwhile, the Surface low will continue to pump plenty of gulf
moisture into the region through tonight in the form of low clouds
and increasing surface dewpoint temperatures into the lower 60s.
Lowered Pops today and tonight as a strong CAP or elevated warm
layer (EML) should prevent convection from forming. However, can`t
rule out a little light drizzle developing tonight or a few
showers beneath the EML.

(Thanksgiving through Tuesday)

..Locally heavy rain possible this Holiday weekend...
..Freezing rain possible across the northwestern Big Country...

The second half of the week is looking quite active with numerous
forecast concerns, to say the least. All available guidance
continues to indicate a prolonged period of rainfall will affect
the forecast area this Holiday weekend. A deep upper-level
trough will remain anchored across the western CONUS, with a pair
of closed mid- level circulations rotating around each other
(Fujiwhara effect), with southwest flow aloft forecast over Texas.
Embedded disturbances will eject northeast in this flow through
the weekend, bringing periodic increases in ascent to our region,
helping increase rainfall coverage/intensity.

Meanwhile, the latest National Hurricane Center (NHC) forecast
takes Hurricane Sandra (currently a hurricane) into the southern
Gulf Of California as a tropical storm (Friday night), weakening
to a tropical depression a little south of the Texas Big Bend
(Saturday night). This is an almost ideal track for a prolonged
feed of mid to upper-level moisture from the system to be advected
over West Central Texas, enhancing our rainfall efficiency. Taking
a closer look at the precipitable water values for 12z Friday, the
models show values ranging from around 1.5 inches along Interstate
20, to 1.7 inches across the Heartland and Northwest Hill Country.
To put this in perspective, the climatology for this time frame is
around 1 inch at Midland and 1.42 inches at Del Rio.

Another piece to this puzzle will be a strong surface cold front
blasting through the area Friday. This front looks to be a
shallow/Arctic front in nature.  This front will enter
Haskell/Throckmorton counties shortly after midnight Friday
morning, and will clear the Interstate 10 corridor by early
afternoon. However, the 850 front looks to bisect the forecast
area Friday and Saturday. Considerable moisture coupled with
isentropic lift over the 850mb front and ascent from the
approaching upper trough/remnants of Sandra will likely lead to a
heavy rainfall potential. This could be even more of a concern
across the northwestern Big Country, where forecast soundings show
enough cooling in the lowest 1000 feet of the atmosphere to make
freezing rain a concern. Our current thinking is the precipitation
rates may help mitigate the potential for any frozen
accumulations, as most of the NAM/GFS soundings show surface
temperatures near 32 degrees.

The much talked about upper trough will be passing by to our
northeast by Monday. Subsidence behind the trough axis will bring
drier air to the region, ending our rain chances.


Abilene  72  62  71  38 /  10  20  60  80
San Angelo  73  64  74  48 /  10  20  50  60
Junction  72  65  72  64 /  10  20  50  60


.SJT Watches/Warnings/Advisories...



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