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

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FXUS64 KEWX 212252

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
552 PM CDT Mon Aug 21 2017

No major changes to the ongoing package. Looking for some MVFR
ceilings to develop predawn primarily along the I-35 corridor and
affect SAT/SSF/AUS through the early morning. Models are showing a
hint at some ceilings out west near Del Rio so have added a tempo
group of MVFR out there. Should see VFR return by late morning with
fair weather cu the rest of Tuesday. Cant rule out a few stray
showers east of I-35 in the Tue afternoon hours but chances are too
low to include in any of the SAT/SSF/AUS tafs.


.PREV DISCUSSION... /ISSUED 354 PM CDT Mon Aug 21 2017/

SHORT TERM (Tonight through Tuesday Night)...

Temperatures remain near to slightly above normal this afternoon and
will do so again tomorrow with isolated thunderstorms occurring
across the coastal plains. Luckily for us, temperatures did pause
briefly in their rise due to the partial eclipse that traversed
across the CONUS.

Showers and a few thunderstorms are ongoing across the coastal
plains as the influence of a large cyclonic gyre shifts towards the
Texas coast where slightly greater instability exists. This activity
will decrease after sunset as atmosphere restablizes.

Expect a near repeat of today`s weather tomorrow as the H5 ridge
slowly breaks down and the TUTT low shifts closer to the Texas coast
in western Gulf. Another round of showers and a few storms will be
likely across the coastal plains. Heat index values will reach into
the 100-104 degree range as well, minus the Hill Country.

LONG TERM (Wednesday through Monday)...

Weather pattern is becoming increasingly concerning for heavy rain
potential in portions of mid-week and especially towards late
week/weekend as model indications suggest increasing tropical
influence. While model trends indicate this trend, more run-to-run
consistency needs to be seen before full confidence can be placed on
some of the more recent rainfall projections. None-the-less, areas of
heavy rain across the region could impact the region late week and
weekend. See below for details.

A longer wave trough axis will shift across the mid-MS Valley and
force a back-door front into north Texas. EC remains bullish on its
southern progress (likely convectively reinforced) and pivots an
axis of rain into at least north portions of the region here in
South-central Texas. Have weighted more towards the EC solution in
its handling of the previous system a few weeks ago. GFS remains
drier with the front remaining farther north at this time. The Hill
Country looks to be the more favored region for rain Wednesday
afternoon and again Thursday. Depending on how far south the front
shifts, pockets of rain could occur as far south as SA and into the
Rio Grande Plains Thursday as well. This does not bode well for what
can potentially occur this upcoming late week and weekend.

If soils become more saturated in the Hill Country and portions of
the area Wed-Thurs, lower absorption rates could pose a flooding and
river flooding risk for the weekend as both EC and GFS model
projections indicate the remnants of what was Harvey to shift
towards the region. Over the past 3-4 model cycles, global models
have come into agreement that in the Day 5-7 period, Harvey could
redevelop into an organized tropical cyclone across the southern
Gulf. Both models indicate a landfall near the mouth of the Rio
Grande River as the system tracks northwest into south-central Texas.
The biggest concern (as with any tropical system here) is heavy
inland rainfall. If this track occurs, high rainfall totals could
occur quickly and result in river and flash flooding. Confidence is
slowly increasing on this possibility. While the most recent run of
global models are suggesting extreme rainfall, we must keep in mind
how they and the system itself will evolve. The remnants of Harvey
remain a weak open wave at this time and model solutions on rainfall
amounts will shift a good amount over the next few days. Please stay
tuned through the week to solutions as extra upper-air balloon data
are ingested for refined rainfall amount potential and system


Austin Camp Mabry              77  99  77  99  76 /   0  -   -   20  20
Austin Bergstrom Intl Airport  75  98  75  99  75 /   0  -   -   20  20
New Braunfels Muni Airport     75  98  75  99  75 /   0  -   -   20  20
Burnet Muni Airport            73  95  73  95  72 /   0  -   -   30  20
Del Rio Intl Airport           77 101  78 102  78 /   0  -   -   20  20
Georgetown Muni Airport        75  97  75  97  74 /   0  -   -   30  20
Hondo Muni Airport             73  99  73 101  73 /   0  -   -   20  10
San Marcos Muni Airport        75  99  75 100  75 /  -   -   -   20  20
La Grange - Fayette Regional   76  99  76 100  76 /  10  10  -   20  20
San Antonio Intl Airport       76  98  76  99  76 /   0  -   -   20  20
Stinson Muni Airport           76  98  75  98  75 /   0  -   -   20  10




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