Area Forecast Discussion
Issued by NWS Austin/San Antonio, TX

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536
FXUS64 KEWX 220000
AFDEWX

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
600 PM CST Sat Jan 21 2017

.AVIATION...
An upper level trough will bring ISOLD SHRA/TSRA through midnight.
Will leave mention out of TAFs as PROBS are less than 30 with KAUS
having the slightly better chances. Biggest concern during this TAF
period is the wind. As the trough moves off to the east, stronger
winds aloft will drop to the surface at times this evening into the
overnight with greater mixing on Sunday keeping winds strong during
the day, before decoupling Sunday evening. For tonight, W to NW
winds increase to 10 to 20 KTs most areas tonight with 15 to 25 KTs
Hill Country, Edwards Plateau, and Rio Grande Plains. OCNL gusts to
35 KTs are expected. For Sunday, NW winds 20 to 32 KTs will prevail
most areas with frequent gusts to 40 KTs. With the temporary runway
configuration at KSAT, the wind direction tonight and more so on
Sunday will lead to crosswind impacts. For Sunday evening, winds
decrease to less than 10 KTs Sunday evening. Otherwise, VFR skies
prevail with BKN-OVC090 this evening and SKC overnight through Sunday
evening, except possibly FEW035 on Sunday at KAUS.

&&

.PREV DISCUSSION... /ISSUED 435 PM CST Sat Jan 21 2017/

SHORT TERM (Tonight through Sunday Night)...
A deepening mid-to-upper level low currently over the NM/TX border
will continue to move into north Texas and southern Oklahoma tonight
and the Lower Mississippi Valley by tomorrow morning. A surface low
pressure system is in the process of developing over the Oklahoma and
Texas panhandles that will continue to deepen and move to the E-SE
tonight. A pre-frontal trough extending from this system into west
Texas and the Rio Grande Plains has helped mix down much drier
westerly winds fluctuating between 10-30 mph sustained with gusts up
to 40 mph. Although most spots are not above Wind Advisory criteria
now, isolated brief instances are occurring for counties west of I-35
and these instances should continue into the evening hours as the
pressure gradient strengthens with the deepening surface and upper
level lows to our north. These W-NW winds will strengthen to 25-30
mph sustained gusting to 40-45 mph and spread to counties along and
east of I-35 after sunrise tomorrow as higher momentum air aloft
(~50 knots at 925 mb) mixes down efficiently. Therefore, we have a
Wind Advisory in place for the counties that need it now west of the
I-35 corridor that expires at 6 pm Sunday. This advisory will be
expanded along and east of I-35 later this evening as these counties
currently do not need a wind advisory, but may need one overnight.

Surface and 20-foot winds gusting to 30 mph are causing near critical
fire weather conditions in the Rio Grande Plains and parts of the
western Hill Country and southern Edwards Plateau where relative
humidity values are at or below 20 percent. The spots of greatest
concern for the rest of this afternoon are in the Rio Grande Plains
into the Coastal Plains mainly south of Highway 90 where temperatures
have climbed in to the upper 80s and even lower 90s (yes, lower 90s
for January 21st). These areas may potentially have locally critical
fire weather conditions, but almost all areas have received 0.75
inches of rain or more over the last week except for portions of
Maverick, Zavala, and Dimmit Counties that have received a bit less
and all areas have no greater than moderate fire danger forecast by
TFS. Nevertheless, considering grasses are cured and winds will
continue to increase through tomorrow afternoon, we felt it was
prudent to issue a Fire Weather Watch now through 6 pm Sunday for all
of South Central Texas as it will not take much for any grass fire
that starts to spread quickly. We have additional concern that the
near summer-like temperatures some spots over the Rio Grande Plains
and Coastal Plains in particular are having today will accentuate
drying to increase fire danger tomorrow that could create critical
fire weather conditions worthy of a Red Flag Warning tomorrow.
Although temperatures will be lower in the 70s, relative humidity
values below 20 percent are still expected in the Rio Grande Plains
in particular and the strong winds will easily spread any grass fires
that develop with. The evening and/or overnight shifts will evaluate
whether any counties need upgrades to a Red Flag Warning for
tomorrow.

Finally, we do have a slight risk of isolated showers and perhaps a
rogue elevated thunderstorm now for the Hill Country spreading to
areas along and NE of a Burnet to New Braunfels to Halletsville line
through Midnight. Any thunderstorms that occur would be very brief as
moisture is very limited and cells that have developed this afternoon
have dissipated before becoming deep enough long enough to generate
lightning. However, lapse rates aloft are still very steep and could
briefly support thunderstorms as the mid-to-upper level disturbance
passes to our north. Temperatures tonight should cool down into the
upper 40s to lower 50s with skies clearing by Midnight behind the
front but strong winds keeping temperatures up. Highs tomorrow are a
bit tricky given the winds and weak nature of cold air advection, but
for now have mid 60s over the northern Hill Country to mid 70s in the
Rio Grande Plains.

LONG TERM (Monday through Saturday)...
Once we move past tomorrow, impactful weather is not expected for
next week aside from possibly Tuesday as another dry front moves
through the region. Temperatures should quickly recover into the 70s
for Monday and upper 70s to mid 80s for Tuesday as relative humidity
values dip into near 20 percent for the Rio Grande Plains and in the
20s elsewhere. However, the winds are not expected to be near as
strong on Tuesday as they will be tomorrow as the pressure gradient
will be much weaker with Tuesday`s disturbance remaining in the
Northern Plains. A cooling trend begins on Wednesday with
temperatures falling near or below normal for Thursday and Friday as
another upper level disturbance digs into the Southern Plains to
cause our next chance of showers late Friday into Saturday.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              51  70  44  76  51 /  20   0   0   0   0
Austin Bergstrom Intl Airport  51  70  43  75  49 /  20   0   0   0   0
New Braunfels Muni Airport     50  70  43  76  48 /  20   0   0   0   0
Burnet Muni Airport            48  65  40  74  49 /  20   0   0   0   0
Del Rio Intl Airport           51  71  41  79  48 /  -    0   0   0   0
Georgetown Muni Airport        50  66  42  74  49 /  20   0   0   0   0
Hondo Muni Airport             48  73  40  78  47 /  10   0   0   0   0
San Marcos Muni Airport        51  70  42  75  48 /  20   0   0   0   0
La Grange - Fayette Regional   52  69  43  73  49 /  20   0   0   0   0
San Antonio Intl Airport       51  71  43  77  50 /  10   0   0   0   0
Stinson Muni Airport           50  72  43  77  49 /  10   0   0   0   0

&&

.EWX WATCHES/WARNINGS/ADVISORIES...
Wind Advisory from 9 AM to 6 PM CST Sunday for the following
counties: Atascosa...Bastrop...Bexar...Caldwell...Comal...De Witt...
Fayette...Frio...Gonzales...Guadalupe...Hays...Karnes...Lavaca...
Lee...Medina...Travis...Williamson...Wilson.

Wind Advisory until 6 PM CST Sunday for the following counties:
Bandera...Blanco...Burnet...Dimmit...Edwards...Gillespie...
Kendall...Kerr...Kinney...Llano...Maverick...Real...Uvalde...Val
Verde...Zavala.

&&

$$

Mesoscale/Aviation...04
Synoptic/Grids...Runyen
AVIATION (......
Public Service/Data Collection...33



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