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

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FXUS64 KEWX 212344
AFDEWX

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
644 PM CDT Thu Sep 21 2017

.AVIATION.../00Z_TAFS/
Isolated to scattered showers and thunderstorms moving in from the
south will be in at least the vicinity of SAT/SSF through about 01Z.
An inversion at 14-15 kft that quickly suppressed convection at AUS
about an hour ago is also in place at the San Antonio terminals, so
confidence on thunderstorms occurring is still relatively low. Thus,
we have only included VCTS at SSF and VCSH at SAT for the next hour
or so and will amend this if necessary. Wind gusts out of the
southeast at 25-30 knots will be possible with the gust fronts
associated with this activity. Winds will generally remain around
10-15 knots this evening before decreasing in the overnight hours.

Once the convection wanes around sunset, the main aviation issue for
the rest of the evening will be the development of MVFR ceilings at
the I-35 sites between 7-8Z. Confidence remains low on the level at
which these ceilings will form, but model guidance has been trending
towards higher ceilings closer to 2000 feet. For now, we have
included ceilings around 1500 feet during the overnight hours before
lifting them above that threshold shortly after sunrise and to VFR by
16Z. DRT may have a brief period of MVFR ceilings sometime after
sunrise through about 17Z, but confidence is too low at the current
moment to include them at this time.


&&

.PREV DISCUSSION... /ISSUED 243 PM CDT Thu Sep 21 2017/

SHORT TERM (Today through Friday)...
The shortwave that is bringing numerous showers and thunderstorms to
the Houston area this afternoon will continue to push eastward and
weaken through the evening and overnight hours. In its wake weak
isentropic lift combined with the low level jet across west Texas
could produce a few isolated showers/storms over the Edwards Plateau
and Rio Grande Plains through the night.

Friday will see the typical summertime sea breeze showers and storms
as high pressure continues to sit over the ArkLaTex region.
Temperatures will continue to run 2-4 degrees above normal for highs
with afternoon heat index values in the mid to upper 90s due to the
Gulf moisture in place across Central Texas

LONG TERM (Friday Night through Wednesday)...
The high pressure holds on for one more day Saturday, with only
isolated showers and storms possible. By Sunday a large upper trough
digs into the Four Corners region and chances for rain begin to rise.
The trough of low pressure slowly pushes eastward so rain chances
will begin along the Rio Grande Plains Sunday into Monday and then
spread eastward for Tuesday through Thursday. The trough helps to
push a cold front, equally slow moving, down into Texas. While there
is some disagreement between the ECMWF and GFS as to the timing of
the front it will act to only enhance rain chances mid week.
Precipitable Water values will range from 1.75-2.25 inches due to
the continued southerly flow ahead of the trough. The best chances
for rain across South Central Texas look to be Tuesday, Wednesday and
Thursday. With the increased cloud cover and rainfall temperatures
early next week will be kept in the upper 80s with indications of at
least slightly cooler temperatures behind the cold front (whenever it
finally comes through). This far out it is too early to pinpoint
when the heaviest rainfall will occur and where. A lot will depend on
the timing of the cold front, which the models still disagree on.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              93  76  91  73  92 /  20  20  10  10  10
Austin Bergstrom Intl Airport  93  75  91  71  92 /  20  20  20  10  20
New Braunfels Muni Airport     93  75  91  72  92 /  20  20  20  10  20
Burnet Muni Airport            91  73  89  71  90 /  20  20  10  10  -
Del Rio Intl Airport           97  77  94  75  93 /  10  20  10  10  10
Georgetown Muni Airport        93  74  91  71  91 /  20  20  10  10  -
Hondo Muni Airport             97  76  94  74  95 /  20  30  10  10  20
San Marcos Muni Airport        93  75  91  72  92 /  20  20  20  10  20
La Grange - Fayette Regional   92  74  91  72  92 /  30  20  20  10  20
San Antonio Intl Airport       94  76  91  74  92 /  20  20  20  10  20
Stinson Muni Airport           94  76  92  74  92 /  20  20  20  10  20

&&

.EWX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

Mesoscale/Aviation...LH
Synoptic/Grids...04
Public Service/Data Collection...YB


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