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

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FXUS64 KEWX 190600
AFDEWX

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

.UPDATE...
Please see the 06Z aviation forecast discussion below.

&&

.AVIATION...
Earlier convection along the Rio Grande south of Del Rio has
dissipated and additional development is not anticipated through the
overnight hours. Otherwise, the latest data continues to suggest low
clouds may struggle to develop overnight as south/southwest flow and
some drier air will prevent widespread low cloud development. We will
continue a VFR forecast overnight and adjust the forecast if needed.

&&

.PREV DISCUSSION... /ISSUED 236 PM CDT Fri Aug 18 2017/

SHORT TERM (Tonight through Saturday Night)...

Continued focus today and tomorrow remains on the elevated heat index
values and temperatures with readings running slightly above normal.
Temperatures near 100F will be common with heat index values
reaching into the 103-108F range each afternoon. Little to no rain is
expected.

A steady H5 ridge of high pressure remains elongated across south-
central Texas eastward to the northern Gulf of Mexico. This
suppression, and drier air aloft per water vapor satellite imagery,
will mean few clouds and no rain chances for much of the region today.
Temperatures will reach the upper 90s and low 100s this afternoon. A
special weather statement is in effect for the heat indices reaching
upwards of 103-107F. Weak upslope flow and stronger heating on the
periphery of the high in Mexico is aiding some showers and
thunderstorms west of the Rio Grande River. While some of this
activity could cross into Val Verde late this afternoon, limited
coverage and impacts are expected.

Another warm night expected with low clouds developing by dawn
Saturday as we repeat the weather from today. While the H5 ridge is
not overly strong (592DM) tomorrow, very weak CAPE due to strong
mixing of the boundary layer will highly limit cloud and convective
potential. Expect another hot (but not overly hot) day as another
special weather statement is likely. Temperatures will fall short of
heat advisory criteria.

LONG TERM (Sunday through Friday)...

Continued status quo late-weekend and early next week as temperatures
top out near 100F each day. A pattern change will occur starting
Tuesday-Thursday next week that could result in greater rain chances
for the region. Fingers crossed!

Water vapor channels currently depict a mid- to upper level-low over
the FL Peninsula and models track this feature across the Gulf of
Mexico through the weekend. By early next week, the feature will be
near the Texas coast. This feature, along with greater moisture in
the mid and upper-levels should aid in at least coastal plain showers
and storms. Both the EC and GFS also indicate a stronger longwave
trough over the Mid-MS valley that will attempt to bring a back-door
front into north Texas. The question at this time will be how strong
will the convection along the boundary be and can it force the line
farther south? The EC is more bullish on bringing more rain to the
region in the QPF signal while GFS keeps most activity north. The
previous instance from just over a week ago yielded more weight to be
placed on the EC. While overall SuperBlend model chances were
reduced, kept at least a 20-30% chance of thunderstorms Wednesday and
potentially into Thursday of next week.

Also of note will be the future track of current Tropical Storm
Harvey. Model indications suggest Harvey to go inland across the
Yucatan Peninsula and possibly re-emerge into the Bay of Campeche.
Majority of model guidance envelope keeps the storm south of the
region. Will provide updates if the track shifts farther north.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry             100  76 100  77  99 /  -    0  -    0  10
Austin Bergstrom Intl Airport 100  75  99  76  98 /  -    0  -    0  10
New Braunfels Muni Airport     99  75  99  75  98 /  -    0  -    0  10
Burnet Muni Airport            97  72  96  73  95 /   0   0   0   0  -
Del Rio Intl Airport          101  77 101  77 100 /   0   0   0   0  -
Georgetown Muni Airport        98  74  98  75  97 /  -    0  -    0  10
Hondo Muni Airport            101  74 100  74 100 /   0   0   0   0  -
San Marcos Muni Airport       100  75  99  75  99 /  -    0  -    0  10
La Grange - Fayette Regional  100  76 100  76  99 /  10   0  10  10  30
San Antonio Intl Airport      100  76  99  76  98 /   0   0  -    0  -
Stinson Muni Airport           98  75  99  76  97 /  -    0  -    0  -

&&

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

$$

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



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