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

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FXUS64 KEWX 182326 AAA
AFDEWX

Area Forecast Discussion...UPDATED
National Weather Service Austin/San Antonio TX
626 PM CDT Fri Aug 18 2017

.AVIATION.../00Z TAFS/
VFR conditions are expected throughout this forecast period. Majority
of model guidance and forecast soundings are indicating more of a
S/SW flow off the surface after 06Z which should lead to less low
cloud development. At this time have elected to go with SCT from
07Z-15Z. Future forecast may need to add in some MVFR cigs during
this time frame. Should see the SE flow increase to 10-15 knots during
the early evening from the sea breeze influence along I-35. By 06z
winds become southerly and decrease to 5-8 knots. Will see S/SE winds
8-12 knots after 16Z Saturday. Any isolated convection this evening
and Saturday afternoon/evening along the Rio Grande should remain at
least 10 nautical miles away from the airport.

&&

.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              77 100  76 100  77 /   0  -    0  -    0
Austin Bergstrom Intl Airport  76 100  75  99  76 /   0  -    0  -    0
New Braunfels Muni Airport     75  99  75  99  75 /   0  -    0  -    0
Burnet Muni Airport            73  97  72  96  73 /   0   0   0   0   0
Del Rio Intl Airport           78 101  77 101  77 /  -    0   0   0   0
Georgetown Muni Airport        74  98  74  98  75 /   0  -    0  -    0
Hondo Muni Airport             74 101  74 100  74 /   0   0   0   0   0
San Marcos Muni Airport        75 100  75  99  75 /   0  -    0  -    0
La Grange - Fayette Regional   77 100  76 100  76 /  -   10   0  10  10
San Antonio Intl Airport       76 100  76  99  76 /   0   0   0  -    0
Stinson Muni Airport           76  98  75  99  76 /   0  -    0  -    0

&&

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

$$

Mesoscale/Aviation...10
Synoptic/Grids...Runyen
Public Service/Data Collection...Williams


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