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

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FXUS64 KEWX 162342

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
642 PM CDT Wed Aug 16 2017

ISOLD SHRA/TSRA continued from Central Texas across the Edwards
Plateau to the Rio Grande to the Serranias del Burro in a plume of
higher moisture content. Have VCTS at KDRT thru 02Z. Expect this
activity to wane with sunset. Cannot rule out an ISOLD SHRA/TSRA in
this area on Thursday, however PROBs too low to mention at any TAF
site. VFR skies prevail this evening. Stratus with MVFR CIGs
redevelops overnight into the early morning hours, around 06Z at
KAUS, KSAT, KSSF and 12Z at KDRT. The stratus will lift to SCT VFR
cumulus late morning, 15Z to 17Z. S to SE winds 9 to 17 KTs this
evening will decrease to 9 KTs or less overnight and then increase
to 9 to 18 KTs on Thursday. Gusts up to 25 KTs are possible most
areas with possibly higher gusts this evening in and near TSRA.


.PREV DISCUSSION... /ISSUED 325 PM CDT Wed Aug 16 2017/

SHORT TERM (Tonight through Thursday Night)...
The isolated showers and thunderstorms that occurred earlier today
over the western Hill Country and Edwards Plateau have generally
dissipated as the weak trough that was over the Texas panhandle
ejects further east into Oklahoma. A weak lagging shortwave is
helping trigger scattered showers and thunderstorms over the higher
terrain of Mexico that may slip into portions of Val Verde County and
maybe east towards the Edwards Plateau and western Hill Country.
However, an inversion above the boundary layer should suppress most
convection from moving into the region. Elsewhere, hot temperatures
are the main story as high pressure is attempting to rebuild back
over the region. Heat index values are still expected to peak in the
105-107 degree range mainly along and east of the Interstate 35
corridor as highs climb into the upper 90s and lower 100s with dew
points in the upper 60s and lower 70s. However, a few spots in the
Coastal Plains will briefly peak in the 108-110 degree range as dew
points are a bit higher. Given the isolated nature of the heat
indices exceeding Heat Advisory criteria, we will continue with the
strongly-worded SPS we currently have for the rest of this afternoon.

Gusty southerly winds sustained at 10-15 mph and gusting to 20-25 mph
are expected to continue into the evening hours due to a greater than
normal pressure gradient associated with a weak front stalling over
western Texas and Oklahoma. Low clouds should quickly move in after
Midnight due to this relatively strong onshore flow to once again
keep low temperatures up in the mid 70s to around 80 degrees. The
mid-to-upper level subtropical ridge off the coast of Louisiana
should expand west and intensify further tomorrow. This should allow
temperatures to increase 1-2 degrees above where they are today with
most areas in the lower 100s aside from some mid to upper 90s in the
Hill Country. Dew point values should decrease more quickly tomorrow
as mixing is a bit more efficient across the region and drier air
moves into the region from the west behind the weak trough. Thus, the
maximum heat index values should decrease a few degrees relative to
today despite the slight increase in temperatures, but an SPS may be
warranted to account for some isolated areas that approach heat index
values of 108 over the Coastal Plains counties.

LONG TERM (Friday through Wednesday)...
High pressure will continue to expand over the region on Friday and
continue to dominate our weather pattern through the weekend. High
temperatures will be in the lower 100s for most spots each day with
mid to upper 90s in the Hill Country. Maximum heat index values
should remain below 108 degrees due to a slightly drier air mass that
that combined with subsidence inversions associated with the ridge
should limit rain chances below 10 percent. A weak trough moving into
southern California and a weak inverted trough moving in from the
Gulf will help weaken the ridge slightly over South Central Texas.
This should help decrease temperatures a few degrees and cause
isolated showers and thunderstorms mainly east of Interstate 35 on
Monday afternoon. The inverted trough should be over the region on
Tuesday to allow for isolated convective activity to expand further
west into the Interstate 35 corridor for Tuesday. Greater coverage of
storms may be possible if we get a bit stronger sea breeze in place
either day, but for now we remained more conservative with the POPs.


Austin Camp Mabry              78 100  77 101  77 /  -   10  10  -   -
Austin Bergstrom Intl Airport  77 100  76 100  75 /  -   10  10  -   -
New Braunfels Muni Airport     76 100  75 100  75 /  -   10  -   -   -
Burnet Muni Airport            75  96  74  97  74 /  -   10  10  -   -
Del Rio Intl Airport           79 100  78 101  78 /  10  10  10  10  -
Georgetown Muni Airport        77  98  76  98  75 /  -   10  10  -   -
Hondo Muni Airport             76 102  75 101  75 /  -   10  -   -   -
San Marcos Muni Airport        77 100  76 100  75 /  -   10  10  -   -
La Grange - Fayette Regional   78 100  76 100  76 /  10  10  10  10  -
San Antonio Intl Airport       78 100  77 100  76 /  -   10  -   -   -
Stinson Muni Airport           77 100  77  99  76 /  -   10  -   -   -




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