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

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875
FXUS64 KEWX 160513
AFDEWX

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
1213 AM CDT Wed Aug 16 2017

.UPDATE... /INCREASE POPS TO LIKELY WRN HILL COUNTRY/

A shortwave lifting out of the higher terrain of Big Bend/Nrn Mexico
in the evening has supplied lift for convection long enough to take
advantage of the nocturnal low level winds in the overnight hours.
The broken convective line of storms that passed through DRT in the
evening is peaking in intensity over Real/Nrn Uvalde Counties and
should propagate the eastern extent of convection east to near a
Sabinal to Comfort to Llano line. Rain chances were raised to likely
over parts of the Wrn Hill Country, but are tapered off dramatically
east of the line mentioned above. Inflow winds should drop off
significantly by around 09Z which should lead to a quick demise of
the convection. Slow eastward progression means Wrn Kerr/Bandera
Counties, Nrn Uvalde County, and much of Real County has a chance to
see a 2 inch downpour. Outside of this area more isolated rainfall
totals of 1/4 to 1/2 inch are expected across the rest of the western
counties.

&&

.PREV DISCUSSION... /ISSUED 756 PM CDT Tue Aug 15 2017/

UPDATE...
The passage of a mid to upper level short-wave over the Trans-Pecos
area has aided showers and thunderstorms to develop across the
western part of Val Verde county late this afternoon into the early
evening. Latest Doppler radar and satellite images indicate storms
moving to the northeast 20 to 25 mph. Also, these images reveal
that storms are decaying with the loss of daytime heating but
expected to linger around for the next several hours. Based on this
assessment, updated the weather grids out west including parts of
the southern Edwards Plateau which includes isolated showers and
thunderstorms through midnight tonight. Kept isolated showers
overnight over same area as latest HRRR model solution shows isolated
activity.

PREV DISCUSSION... /ISSUED 636 PM CDT Tue Aug 15 2017/

AVIATION...
SHRA/TSRA continue from West Central Texas to the Serranias del
Burro. Have introduced VCSH to KDRT TAF 01z-05z and will monitor for
prevailing TSRA impacts, including gusty winds. SHRA/TSRA will wane
after sunset with loss of heating, then redevelop over these western
areas on Wednesday as moisture axis and weak shear axis remains
there. Will monitor radar and model trends for later impacts to KDRT.
No impacts are expected at KAUS, KSAT, KSSF other than cirrus clouds.
VFR skies this evening. Stratus with mainly MVFR CIGs develops
overnight into morning. Stratus then lifts to VFR FEW cumulus late
morning and prevails through evening. S to SE winds 10 to 20 KTs with
gusts to 25 KTs this evening and again midday to evening Wednesday,
otherwise, 5 to 12 KTs are expected. Wind gusts to 40 KTs are
possible with the stronger TSRA.

PREV DISCUSSION... /ISSUED 312 PM CDT Tue Aug 15 2017/

SHORT TERM (Tonight through Wednesday Night)...
The early morning upper air observations show an upper trough in place
over the western U.S. with the subtropical high centered over south
Florida. A little closer to home, satellite data also shows an axis
of higher moisture in place from southwest Texas into far north
central Texas. Precipitable water values range from 1.7 to near 2.0
inches according to early afternoon data.

The above mentioned axis of higher moisture will move very little
tonight and Wednesday. This will result in a continued chance for
showers and thunderstorms across the southern Edwards Plateau. Hi-res
models show most convection will remain northwest of a Del Rio to
Rocksprings line. Coverage of showers and storms should be rather
low, so we will keep chances in the 20-30% range. We could also see
a few showers and storms develop Wednesday afternoon across the
coastal plains and Highway 77 corridor and will continue to mention
low chances (20%) in the latest forecast. Otherwise, expect another
mild night with increasing cloud cover after midnight and lows in the
70s. Another hot day is in store for Wednesday as highs once again
top out in the mid 90s to near 100. The heat combined with a
continued moist southeasterly flow in the low-levels will result in
elevated heat index values Wednesday afternoon and early evening. As
of now, it appears areas along and east of I-35 will be very close to
needing a Heat Advisory.

LONG TERM (Thursday through Tuesday)...
The forecast for the remainder of the work week into early next week
will generally be dominated by a slowly expanding subtropical ridge
axis. However, the medium range models do show some inverted
mid/upper troughs moving through the Gulf of Mexico over the next
several days. One trough is currently forecast to move into the
western Gulf by early Thursday, with another scheduled for early
Monday. The second system appears to be stronger, but there is some
disagreement with regards to where this system will move inland.
While these inverted troughs may bring a brief opportunity for
rainfall, suspect chances will remain confined to the coast.
Otherwise, it appears high temperatures will continue to remain
roughly 3-5 degrees above normal, with overnight lows a few degrees
above normal. During this period of above normal temperatures, please
continue to exercise proper heat safety.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              78 101  77 101  76 /  -   -   -   10  -
Austin Bergstrom Intl Airport  77 100  76 100  75 /  -   -   -   10  -
New Braunfels Muni Airport     77 101  75 101  75 /  -   -   -   10  -
Burnet Muni Airport            75  97  74  97  73 /  -   -   -   10  -
Del Rio Intl Airport           80 102  78 102  78 /  10  10  -   10  -
Georgetown Muni Airport        77  98  76  99  75 /  -   -   -   10  -
Hondo Muni Airport             76 103  75 103  74 /  10  10  -   10  -
San Marcos Muni Airport        77 100  75 100  75 /  -   -   -   10  -
La Grange - Fayette Regional   78 100  76  99  76 /  -   10  -   10  -
San Antonio Intl Airport       78 101  77 101  76 /  -   10  -   10  -
Stinson Muni Airport           78 100  77 100  76 /  -   10  -   10  -

&&

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

$$

Mesoscale/Aviation...Runyen
Synoptic/Grids...Oaks



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