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

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713
FXUS64 KEWX 220554
AFDEWX

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
1254 AM CDT Tue Aug 22 2017

.AVIATION.../06Z TAFS/

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 and modified toward persistence from Monday
morning. Should see VFR skies return for the rest of the TAF periods
as the surface pressure gradient begins to relax further in response
to both the approach of a weakening TUTT low over the Nrn Gulf and
the potential developing tropical wave moving toward the Bay of
Campeche Wednesday morning.

&&

.PREV DISCUSSION... /ISSUED 923 PM CDT Mon Aug 21 2017/

UPDATE...
Isolated showers and thunderstorms continue across far eastern zones
mid evening. A minor update was required to extend mention of this
activity across these zones through midnight. Expect these isolated
showers and storms to end around or after midnight with loss of
heating.

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
impacts.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              77  99  76  97  76 /  -   20  20  30  30
Austin Bergstrom Intl Airport  75  99  75  97  75 /  -   20  20  30  20
New Braunfels Muni Airport     75  99  75  98  75 /  -   20  20  30  20
Burnet Muni Airport            73  95  72  92  72 /  -   30  20  40  20
Del Rio Intl Airport           78 102  78 100  77 /  -   20  20  30  20
Georgetown Muni Airport        75  97  74  94  74 /  -   30  20  30  30
Hondo Muni Airport             73 101  73  99  73 /  -   20  10  30  20
San Marcos Muni Airport        75 100  75  99  74 /  -   20  20  30  20
La Grange - Fayette Regional   76 100  76  98  76 /  -   20  20  30  30
San Antonio Intl Airport       76  99  76  97  76 /  -   20  20  30  20
Stinson Muni Airport           75  98  75  97  75 /  -   20  10  30  20

&&

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

$$

Mesoscale/Aviation...Oaks
Synoptic/Grids...Hampshire



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