Special Weather Statement, NWS Austin/San Antonio, TX

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
622 AM CDT Sun Aug 15 2021

.AVIATION...

No major changes to the forecast this morning as it's relatively
quiet with light to calm winds and just a little MVFR CIG
development near SAT/SSF that should quickly scatter out after
sunrise. A complex of showers and thunderstorms has developed early
this morning well to our north, and although most high- resolution
model guidance depicts this activity dissipating through the morning
the CAMS have not had a good handle on it. Regardless, some
scattered shower and isolated thunderstorm activity could impact the
I-35 terminals this afternoon although coverage remains somewhat
uncertain. Heavy rain may reduce visibility and some gusty winds
cannot be ruled out in the strongest storms, but confidence in
impacts to the terminals is low. Otherwise, expect light winds
through the period and VFR conditions to prevail.

&&

.PREV DISCUSSION... /ISSUED 222 AM CDT Sun Aug 15 2021/

SHORT TERM (Today through Monday)...
The upper air pattern early this morning across the southern CONUS
consists of a weak southward-sinking trough across the MS River
Valley as the sub-tropical ridge is shunted back to the west. Very
gradual height falls are progged across TX over the next 24-48
hours. A few showers and storms made it to the southern Edwards
Plateau and Western Hill Country in the evening hours before
dissipating with the loss of daytime heating, but they've left a
weak convergence axis from W to E across central portions of the
CWA. A few tiny showers popped up in their wake around 04-05Z, but
we're anticipating a dry night as well as much of the AM with a
stable boundary layer in place.

Some destabilization will take place after sunrise with low level
lapse rates increasing quickly through the day, and CAMS are in good
agreement that isolated to scattered shower and thunderstorm
development will take place near or north of our northern border
sometime later in the morning or perhaps around midday. This
activity will increase in coverage during the afternoon and slowly
sink south across the region before again dissipating after sunset.
Some briefly gusty winds are possible in any stronger storms, with
locally heavy rainfall also potentially in the cards. Most locations
will likely see a half inch or less of rain, but 1-3" could be
realized in a few locations. HREF max values of 3-4+" cannot be
completely ruled out which could lead to advisory-level minor
flooding concerns. WPC's Excessive Rainfall Outlook depicts a
Marginal Risk across most of the CWA, with the exception of the
Winter Garden region.

Today will be the coolest of the week for many as rain could keep
highs in the mid-upper 80s in a few spots. Most locations should
still reach the 90s, warmest along the Rio Grande. Similar
temperatures are forecast for Monday give or take a couple degrees
dependent on rainfall/cloud cover. Additional diurnally driven
showers and storms are possible on Monday, but coverage may be a tad
lower than today and precipitation amounts should be a lower also as
the NW flow aloft will act to reduce PWATS and thus the risk for
locally heavy rain as well. Tough to pick out favored locations for
development on Monday given the nebulous forcing so broad-brushed
chance POPs are forecast Monday afternoon except once again across
the Winter Garden region.

LONG TERM (Monday Night through Saturday)...
On Tuesday afternoon a weak trough axis will be pushing into West
Texas which should allow for continued afternoon shower and
thunderstorm chances across much of the area. The northwestern CWA
will likely have the higher PoPs as upper lift is expected to be
strongest over this region. Highs Tuesday should remain in the lower
to upper 90s for most spots.

The trough axis is expected to become less defined and shift to the
east a bit with upper ridging strengthening in the northern Gulf of
Mexico. This should equate to slightly lower PoPs for the area on
Wednesday but will still hold onto 20-30 PoPs for most of the area.
High temperatures will likely respond with a slight increase of 1-2
degrees compared to Tuesday.

The forecast will dry out for the most part on Thursday and Friday as
weak ridging nudges in from the east. Can't rule out an isolated
shower or storm in the Coastal Plains or western CWA on Thursday.
Highs Thursday and Friday will range from the upper 90s to 102 across
the area. Heat index values will be near 105-109 degrees for areas
along and east of I35 during this time period as well.

A slight chance of rain returns to the forecast on Saturday, but this
forecast will be highly dependent on what happens to Tropical Storm
Grace 7 days from now. Medium-range models are all over the place in
comparison with each other and within each individual model's run-
to-run consistency.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              92  75  93  75  96 /  50  20  40  -   30
Austin Bergstrom Intl Airport  92  73  92  74  94 /  50  20  30  -   20
New Braunfels Muni Airport     93  73  93  74  95 /  50  20  30  -   20
Burnet Muni Airport            90  73  92  74  92 /  50  20  40  10  30
Del Rio Intl Airport           97  77  97  78  97 /  20  20  30  20  30
Georgetown Muni Airport        91  73  92  74  94 /  50  20  40  -   30
Hondo Muni Airport             93  74  94  74  94 /  40  20  30  10  20
San Marcos Muni Airport        93  73  93  74  94 /  50  20  30  -   20
La Grange - Fayette Regional   94  76  94  76  95 /  40  20  40  -   20
San Antonio Intl Airport       92  75  93  75  94 /  50  20  40  10  20
Stinson Muni Airport           94  76  94  76  95 /  40  20  40  10  20

&&

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

Short-Term/Aviation...KCW
Long-Term...Hampshire

Hazardous Weather Outlook
National Weather Service Austin/San Antonio TX
301 AM CDT Sun Aug 15 2021

TXZ171>173-183>194-202>209-217>225-228-160815-
Llano-Burnet-Williamson-Val Verde-Edwards-Real-Kerr-Bandera-
Gillespie-Kendall-Blanco-Hays-Travis-Bastrop-Lee-Kinney-Uvalde-
Medina-Bexar-Comal-Guadalupe-Caldwell-Fayette-Maverick-Zavala-
Frio-Atascosa-Wilson-Karnes-Gonzales-De Witt-Lavaca-Dimmit-
301 AM CDT Sun Aug 15 2021

This Hazardous Weather Outlook is for South-Central Texas..

.DAY ONE...Today And Tonight.

Scattered showers and thunderstorms are expected this afternoon
and early evening. The strongest activity could produce locally
heavy rainfall with isolated amounts up to 3 inches.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not anticipated.

Special Weather Statement
National Weather Service Austin/San Antonio TX
1238 PM CDT Sun Aug 15 2021

TXZ190-191-151815-
Blanco TX-Hays TX-
1238 PM CDT Sun Aug 15 2021

...A strong thunderstorm will impact portions of northwestern Hays
and northeastern Blanco Counties through 115 PM CDT...

At 1238 PM CDT, Doppler radar was tracking a strong thunderstorm over
Pedernales Falls State Park, or 11 miles northwest of Dripping
Springs, moving southeast at 15 mph.

HAZARD...Winds in excess of 40 mph and half inch hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible.

Locations impacted include...
Dripping Springs, Henly, Pedernales Falls State Park, Cypress Mill
and Mount Gainor.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

Torrential rainfall is also occurring with this storm and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 3039 9827 3033 9813 3024 9801 3007 9819
      3032 9834
TIME...MOT...LOC 1738Z 311DEG 13KT 3028 9823

MAX HAIL SIZE...0.50 IN
MAX WIND GUST...40 MPH

BRADY