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

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FXUS64 KEWX 210548

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
1248 AM CDT Sat Oct 21 2017

No significant changes from the ongoing TAFs. AUS has dropped to MVFR
and the other airports will follow within the next couple of hours.
CIGs will continue to drop overnight with LIFR expected for a couple
of hours around sunrise. Improvement will be slow through the morning
and all airports will reach VFR by early afternoon. Shower and
thunderstorms will develop ahead of a cold front at the end of the 24
hour period. We have included TSRA at AUS and SAT after 06Z.


.PREV DISCUSSION... /ISSUED 932 PM CDT Fri Oct 20 2017/

Aircraft soundings at SAT and SSF show a pretty stout cap over the
I-35 corridor at 700-800 mb with a weaker cap evident at the Houston
terminals. Therefore, thunderstorms are not expected tonight as the
lack of surface forcing and significant shortwave activity should
allow this strong cap to hold easily. Hi-res models also show very
little (if any) shower activity over the region tonight with patchy
fog looking more likely after Midnight, so we have removed the 20
POPs that we previously had for tonight from the forecast and added
in patchy fog for the eastern half of the CWA. Mixing should be a bit
stronger tomorrow morning than it was today, so this fog should lift
by mid-morning, with isolated to scattered shower activity increasing
in coverage later tomorrow morning mainly east of I-35. A slight
chance for isolated thunderstorms is still possible along and east of
I-35 tomorrow afternoon north of San Antonio, with the best chances
further east in the Coastal Plains. Aside from retrending the grids
based on observations, no other changes were made to the forecast.

PREV DISCUSSION... /ISSUED 250 PM CDT Fri Oct 20 2017/

SHORT TERM (Today through Saturday)...
Other than a few isolated showers across areas east of I-35, and a
few sprinkles along the I-35 corridor all of the precipitation today
has been concentrated over the Houston area. Through the afternoon
due to the moist southerly flow there could still be a couple of
isolated showers or storms. For tonight and tomorrow morning a few
streamer showers will be possible mainly across areas along and east
of I-35. The typical low clouds and patchy fog that Central Texas
sees with southerly flow is also forecast. By Saturday afternoon with
the added day time heating an isolated thunderstorm will be
possible, but chances remain low and confined to the eastern areas
due to capping and where the focus of the more significant moisture
resides. Temperatures will be warm ahead of the front expected
Saturday night. Highs for Saturday will be in the upper 80s with
south winds continuing. This will result in afternoon heat index
values in the lower 90s. As you venture out enjoying your weekend
plans be on the lookout for the isolated storms, and be aware of the
hot and humid October afternoon expected on Saturday.

LONG TERM (Saturday Night through Thursday)...
The biggest weather feature of the next seven days, and the long
advertised front will arrive Saturday night. The front is now within
the time frame of several high resolution models from the Texas Tech
WRF to the ARW and NMM. As the trough pivots into Texas and the front
moves south showers and thunderstorms will form along and ahead of
the front. While the focus of the shower and thunderstorm activity,
including the best chance for strong to severe storms, will be north
of the area - from DFW into Oklahoma - there is a chance that Central
Texas could see a few strong to severe storms with the front. Model
soundings are showing a weakly capped or uncapped atmosphere with
1500-2000 j/kg of CAPE and plenty of shear could lead to these strong
to severe storms. Because of this the Storm Prediction Center has
extended the marginal risk area southwestward to include much of the
I-35 corridor. The primary threat will be strong thunderstorm winds
with the line of storms, along with hail. The current timing of the
front looks to be between 5am and 9am for the Austin Metro area, 9am
to noon for the San Antonio Metro, and out of our southern counties
along the coastal plains by 1pm to 3pm in the afternoon. Behind the
front skies will clear and winds will shift out of the north and be
gusty at times up to 25 mph.

Temperature behind the front will cool slightly with highs on Sunday
only expected in the upper 70s. Next week will be dry and mostly
sunny through the week. Another front arrives on Tuesday which will
help reinforce the north winds, dry conditions, and slightly cooler
temperatures. The next rain maker could be another front, just beyond
the forecast period, late next week into next weekend.


Austin Camp Mabry              86  65  77  52  81 /  20  80  40  -    0
Austin Bergstrom Intl Airport  87  66  76  49  82 /  30  80  50  -    0
New Braunfels Muni Airport     88  66  78  50  81 /  20  70  50  -    0
Burnet Muni Airport            84  60  74  48  80 /  20  80  30  -    0
Del Rio Intl Airport           85  62  80  52  83 /  -   40  10  -    0
Georgetown Muni Airport        86  63  75  49  81 /  20  80  40  -    0
Hondo Muni Airport             88  65  82  47  83 /  10  70  40  -    0
San Marcos Muni Airport        87  66  78  50  81 /  20  80  50  -    0
La Grange - Fayette Regional   87  68  77  50  79 /  40  60  70  -    0
San Antonio Intl Airport       88  67  80  52  82 /  10  70  40  -    0
Stinson Muni Airport           90  68  80  53  82 /  10  70  50  -    0




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