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

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909
FXUS64 KEWX 251204 AAA
AFDEWX

Area Forecast Discussion...UPDATED
National Weather Service Austin/San Antonio TX
704 AM CDT Mon Sep 25 2017

.AVIATION...
/12Z TAFS/
Shower and thunderstorm activity continues across the Rio Grande and
Edwards Plateau while affecting KDRT for the next several hours. LIFR
cigs are expected for KAUS for the next few hours while the San
Antonio airports should remain under IFR conditions next couple of
hours. Cigs and vbsys should improve across all areas sites to VFR no
later than 18Z. Convection out west may take a break for few hours
but activity returns and remains through the overnight hours.
MVFR/IFR conditions are expected to return overnight to all sites as
low levels get saturated. Southeast winds 8 to 10 knots across the
I-35 sites and 10 to 15 knots with gusts up to 20 knots along the Rio
Grande and KDRT.

&&

.PREV DISCUSSION... /ISSUED 514 AM CDT Mon Sep 25 2017/

SHORT TERM (Today through Tuesday)...
Early morning radar data shows convection is underway across most of
Val Verde county as well as to the south over northern Coahuila,
Mexico. While a little difficult to discern at the present time, it
appears we could be seeing the beginning of an MCV developing
southwest of Del Rio. Otherwise, the water vapor satellite loop shows
a tropical moisture connection from Tropical Storm Pilar into the
southwestern portion of Texas, including the Rio Grande plains.

Given recent radar trends along with hi-res models, we will go with
high rain chances along the Rio Grande today. A moist air mass is
already in place as evidenced by the 25/00Z DRT sounding with a
precipitable water value just shy of 2". Some locally heavy rain is
possible today given the moist conditions and training of showers and
thunderstorms. Across the remainder of the region, we should see
isolated to scattered showers and thunderstorms, especially during
the afternoon hours during peak heating hours. Cloud cover and
precipitation should keep highs generally in the 80s, except south of
Highway 90/west of I-35 where some lower 90s are forecast.

The concern for a heavy rain event across the Rio Grande plains and
southern Edwards Plateau beginning Tuesday continues to grow given
recent model consistency along with the very latest round of model
guidance. Deep moisture is already in place and will remain in place
as additional moisture and upper level energy from Tropical Storm
Pilar move northward into the region. While it will be difficult to
time these shortwaves, it appears one stronger wave will move into
the Rio Grande plains late this afternoon, with an even stronger wave
Tuesday afternoon. With this in mind, we have increased rain chances
across the Rio Grande plains on Tuesday and Tuesday night. Forecast
soundings continue to show tall, skinny CAPEs along with precipitable
water values just shy of 2.5". All this leads to a continued threat
for heavy rain on Tuesday and we will likely need a Flash Flood Watch
for the western portion of our area beginning Tuesday.

LONG TERM (Tuesday Night through Sunday)...
The weather pattern will not change significantly for Tuesday night
as heavy rainfall concerns continue along the Rio Grande and southern
Edwards Plateau. If anything, some of the heavier rains may nudge
eastward into the Highway 83 corridor. On Wednesday, a cold front is
expected to move southward across west Texas. The leading edge of
this front should manage to push southward into the western Hill
Country and southern Edwards plateau during the afternoon hours. This
front will likely aid in the development of showers and storms. As
the front moves southward Wednesday night into Thursday morning,
concerns for additional heavy rains may continue across portions of
the Rio Grande plains, especially if the ECMWF verifies. With this
in mind, we have increased rain chances for Wednesday night and
Thursday morning across the mentioned areas. Storm total precipitation
amounts from Tuesday into early Thursday morning have been increased
to 4 to 6" with isolated amounts near 9". The heaviest amounts are
expected to occur west of Highway 83. Farther east, we should see
average amounts drop into the 1-3 inch range along Highway 281.

Some drier air should begin to filter in from the north beginning
Friday. This should bring a gradual decrease in rain chances from
east to west for Friday into the upcoming weekend.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              89  73  87  73  87 /  30  20  40  40  40
Austin Bergstrom Intl Airport  89  72  87  72  86 /  30  20  40  40  40
New Braunfels Muni Airport     88  73  86  72  86 /  30  20  50  50  40
Burnet Muni Airport            86  71  84  70  82 /  30  20  40  60  50
Del Rio Intl Airport           87  73  85  71  84 /  70  80 100 100  80
Georgetown Muni Airport        88  72  87  72  85 /  20  20  30  40  40
Hondo Muni Airport             91  74  88  73  88 /  50  50  70  70  70
San Marcos Muni Airport        88  73  86  72  87 /  30  20  50  50  40
La Grange - Fayette Regional   89  73  89  73  88 /  30  10  30  30  30
San Antonio Intl Airport       88  74  86  73  86 /  40  30  60  60  50
Stinson Muni Airport           88  75  86  74  86 /  40  40  60  60  50

&&

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

$$

Mesoscale/Aviation...17
Synoptic/Grids...24



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