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

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000
FXUS64 KEWX 191155 AAA
AFDEWX

Area Forecast Discussion...UPDATED
National Weather Service Austin/San Antonio TX
655 AM CDT Sat Aug 19 2017

.UPDATE...
Please see the 12Z aviation forecast discussion below.

&&

.AVIATION...
SCT-BKN low clouds have managed to develop at SAT and SSF this
morning and based on recent observations and satellite trends, we
will keep a TEMPO group for MVFR cigs through 13Z. Otherwise, VFR
conditions are in store today as south-southwest winds along I-35
gradually become southeast by late afternoon. Out west at DRT, VFR
conditions are in store as east winds this morning become southeast
around 14Z.

&&

.PREV DISCUSSION... /ISSUED 344 AM CDT Sat Aug 19 2017/

SHORT TERM (Today through Sunday)...
Continued influences of a stubborn hot air mass continue today and
tomorrow. Highs again right around 100 degrees for much of the I-35
corridor with heat indices ranging from 101-108. The higher end of
these values will be seen again in the southeast zones. Surface winds
are expected to remain southerly and southeasterly today as a surface
high is located over the Louisiana coast.

Over the last couple days, isolated showers and storms have developed
despite all clear indications from CAMs and other short range models.
Again this morning the hi-res suite shows the area shower-less,
however GFS and ECWMF deterministic produce isolated showers again to
the northwest. Looking at forecast soundings across the area, parcels
will be struggling against a pretty dry column and an unfavorable
wind profile above 600 mb. As a result, still feel that a dry
forecast is the right call, but did include 10 PoPs along the
southeast and northwest zones for the afternoon.

LONG TERM (Sunday Night through Friday)...
A pattern change looks to be on the horizon beginning mid week as a
TUTT low traverses the Gulf of Mexico, moving west. This will bring
at first, welcome relief of 2-3 degrees in Max T, then an uptick in
PoP chances as the low pushes west of the CWA. This pattern has been
pretty consistently advertised now in mid range models.

The more notable feature comes late week as a frontal passage is
progged to push south and into Texas Wednesday night through Friday.
At the moment, the 00Z GFS deterministic solution is significantly
more dry than its ECMWF counterpart. With the ridge centered over
northern Mexico, whatever convection occurs with the frontal passage
should be able to push far enough south to bring showers at least to
the northern zones late Wednesday night into Thursday morning. The
question will be how far south? The GFS solution stalls the front
along our northeast border with HGX/FWD but with 850 mb flow parallel
to the boundary, could result in some locally heavy rainfall.
Additionally, the nose of the 850 mb LLJ would intrude nicely into a
2+" PWAT environment along the stalled boundary...so if this solution
comes to fruition, could result in some meaningful rain for the
northern I-35 corridor, perhaps extending as far south as Williamson
County.

Come Friday, GFS/ECMWF/Canadian all develop some sort of tropical
disturbance off the Yucatan and pushes it quickly north along the
Mexican coastline, coming on shore just south of Brownsville. If so,
this would put the southern half of the state under a very rich
moisture regime for next weekend, possibly leading to more heavy
rainfall chances. More to come on this with more model evolution.

&&

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

&&

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

$$

Mesoscale/Aviation...24
Synoptic/Grids...TB3



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