Special Weather Statement, NWS Austin/San Antonio, TX

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
656 PM CDT Tue May 11 2021

.AVIATION...
Short term concern is the ongoing convection across the region.
Currently storms in the vicinity of SAT and SSF. Storms will be
possible for the next several hours in the San Antonio and Austin
areas. Strong gusty winds will be the biggest impact from storms with
gusts up to 25 kts possible. Ceilings will also lower to MVFR in
storms. Otherwise ceilings will be VFR until later this evening when
they will lower to MVFR and later to IFR. Ceilings will stay IFR
through the morning Wednesday and lift only to MVFR during the
afternoon.

At DRT, there may be showers for the next few hours, but otherwise
will be VFR. Ceilings will drop to MVFR overnight. There is a chance
for TS overnight which could drop conditions to LIFR, but
probability is low.

&&

.PREV DISCUSSION... /ISSUED 347 PM CDT Tue May 11 2021/

UPDATE...
We have issued a Severe Thunderstorm Watch most of South Central
Texas. Conditions are favorable for the formation of severe
thunderstorms capable of producing hail up to two inches, wind gusts
up to 70 mph, and a tornado or two. The watch is in effect until 10
pm this evening.

PREV DISCUSSION... /ISSUED 251 PM CDT Tue May 11 2021/

SHORT TERM (Tonight through Wednesday Night)...

A diffuse frontal boundary from west to east across south-central
Texas will eventually push south this evening, likely aided by
storms that are expected to increase in coverage and move eastward
across the region later this afternoon through the evening hours. At
19z, areas south of the front were mostly sunny with temperatures in
the 80s to near 90 and dew points in the 70s, while north of it
temperatures were in the 60s and low 70s with some light fog and low
stratus. Temperature gradient from La Grange to burnet is nearly 30
degrees!

An approaching shortwave is already setting off convective
development over the SDB mountain range in Mexico, and some WAA
forced elevated storms continue from just east of Sonora
northeastward into the DFW metroplex, with some of that activity now
into our region from Kerr to Burnet counties although with little
thunder until you cross into Lampasas. In addition, a weak
convergence axis stretches from north of Bryan, TX to near Gonzales
although convective development in our area has been minimal at best.

Even in the cool sector, elevated CAPE in excess of 2000 J/kg exists
above the inversion with steep lapse rates at mid-levels on the
order of 7.8-8C/km. And SBCAPE has been able to build to 2500-4000
J/KG in the warm sector today. Deep layer shear is a little weaker
today, but still decent west, with the special DRT sounding this
afternoon showing 34 knots 0-6km. As the storms in Mexico slowly
enter the area this evening, they will pose the greatest risk for
large to very large hail and a very low chance for an isolated
tornado south of the front where SRH could briefly increase. Any
supercells will likely quickly grow upscale though.

HRRR still hones in on some storms east of I-35 along the existing
convergence axis this afternoon and isolated severe hail or a brief
downburst could be possible there if storms are able to develop
which appears 50/50 at best. Storms are likely to grow into a SW/NE
oriented quasi-complex through the evening hours and pose a marginal
to slight risk of large hail or damaging winds. There is also a low
chance for isolated flash flood impacts with rainfall amounts of up
to three inches in spots which could occur over already saturated
ground. Flash flood guidance is lowest today from San Antonio west
and southwest to the Rio Grande so those will be the areas to watch.
Severe threat should mostly end by midnight at the latest. Some
lingering showers and storms may remain behind the front but
coverage should decrease quite a bit after midnight.

We have kept some low chances of showers and a few thunderstorms in
the forecast through much of Wednesday as some weak isentropic lift
in conjunction with weak elevated instability could lead to isolated
activity at times, especially near the Rio Grande in the AM.
Coverage will be low, and impacts are generally not expected. Skies
will remain cloudy through the day, and it will be quite cool for
this time of year with highs in the low to mid 60s north and low to
perhaps mid 70s south. In fact, Bergstrom will likely flirt with
record low maxT tomorrow. Wednesday night lows should fall into the
50s and lower 60s with any remaining shower chances relegated to far
southwestern portions of the region overnight, if at all.

LONG TERM (Thursday through Tuesday)...

A northwest to west flow aloft is forecast to prevail Thursday and
Friday. Surface winds are expected to turn from northeast to east
on Thursday for most areas with southerly winds returning across the
entire area by midday on Friday. A warming trend is on the way with
highs in the 70s on Thursday and upper 70s to mid 80s on Friday.
Clouds are expected to linger for most of the morning period and
scattered mid to late afternoon both Thursday and Friday.

Showers and storms return across south central Texas on Saturday as
several mid to upper level short waves move from west Texas into
central Texas. The activity diminishes late Saturday night through
early Sunday morning, however, picks up on Sunday as another short
wave traverses across the Southern Plains.

The wet period continues into early next week as the parade of
short waves continue to push over the area. Better chances for rain
come on Tuesday areawide as an upper level system travels across the
four corners region and opens as it moves over the Southern Plains.
The GFS solution pushes a cold front across the area during that time
frame while the ECMWF and CMC models keep a surface southerly flow
through the extended forecast. Time will tell.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              62  67  58  75  57 /  70  30  -   -    0
Austin Bergstrom Intl Airport  62  68  57  75  56 /  70  30  -   -    0
New Braunfels Muni Airport     63  69  59  77  58 /  60  40  -   -    0
Burnet Muni Airport            58  65  55  73  56 /  50  20  -    0   0
Del Rio Intl Airport           66  70  63  77  64 /  60  50  20  -   -
Georgetown Muni Airport        60  66  57  74  56 /  70  30  -    0   0
Hondo Muni Airport             65  71  59  77  59 /  50  30  10  -    0
San Marcos Muni Airport        62  68  57  76  56 /  60  30  -   -    0
La Grange - Fayette Regional   65  70  60  77  59 /  60  40  10  -    0
San Antonio Intl Airport       64  70  60  75  59 /  70  30  -   -    0
Stinson Muni Airport           65  72  61  77  61 /  60  30  -   -    0

&&

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

Short-Term/Aviation...05
Long-Term...Platt
Decision Support...Runyen

Hazardous Weather Outlook
National Weather Service Austin/San Antonio TX
418 PM CDT Tue May 11 2021

TXZ171>173-183>194-202>209-217>225-228-122130-
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-
418 PM CDT Tue May 11 2021

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

.DAY ONE...Tonight.

Strong to severe storms are possible again today and tonight with
large hail and damaging winds being the primary hazards. An
isolated tornado is also possible.

Additionally, locally heavy rainfall is possible today and
tonight, which could result in localized flooding over areas that
may have recently seen soils become saturated.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not anticipated.

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE AUSTIN/SAN ANTONIO TX
715 PM CDT TUE MAY 11 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0714 PM     FLOOD            2 W BIG WELLS           28.57N 99.60W
05/11/2021                   DIMMIT             TX   TRAINED SPOTTER

            YARD FLOODED.

&&

BF

Special Weather Statement
National Weather Service Austin/San Antonio TX
724 PM CDT Tue May 11 2021

TXZ172-190>192-120115-
Blanco TX-Hays TX-Burnet TX-Travis TX-
724 PM CDT Tue May 11 2021

...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN HAYS...WEST CENTRAL
TRAVIS...NORTHERN BLANCO AND SOUTH CENTRAL BURNET COUNTIES UNTIL 815
PM CDT...

At 724 PM CDT, Doppler radar was tracking a strong thunderstorm over
Johnson City, or 8 miles south of Round Mountain, moving east at 25
mph.

Half inch hail and winds in excess of 40 mph will be possible with
this storm.

Locations impacted include...
Round Mountain, Johnson City, Sandy, Pedernales Falls State Park,
Spicewood and Cypress Mill.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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.

&&

A Severe Thunderstorm Watch remains in effect until 1000 PM CDT for
south central Texas.

LAT...LON 3019 9844 3037 9850 3052 9812 3024 9803
TIME...MOT...LOC 0024Z 251DEG 23KT 3031 9839

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE AUSTIN/SAN ANTONIO TX
727 PM CDT TUE MAY 11 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0724 PM     HAIL             2 N JOHNSON CITY        30.31N 98.41W
05/11/2021  U0.75 INCH       BLANCO             TX   PUBLIC

            REPORT FROM MPING DIME (0.75 IN.).

&&

BF

Special Weather Statement
National Weather Service Austin/San Antonio TX
734 PM CDT Tue May 11 2021

TXZ223>225-120115-
Lavaca TX-De Witt TX-Gonzales TX-
734 PM CDT Tue May 11 2021

...SIGNIFICANT WEATHER ADVISORY FOR NORTHEASTERN DEWITT...EAST
CENTRAL GONZALES AND WEST CENTRAL LAVACA COUNTIES UNTIL 815 PM CDT...

At 732 PM CDT, Doppler radar was tracking a strong thunderstorm near
Hochheim, or 7 miles southwest of Shiner, moving east at 15 mph.

Half inch hail will be possible with this storm.

Locations impacted include...
Shiner, Hochheim, Dreyer, Sweet Home, Glaze City, Mount Olive, U.S.
Highway 90 Alternate.

A Severe Thunderstorm Watch remains in effect until 1000 PM CDT for
south central Texas.

LAT...LON 2926 9734 2934 9738 2953 9719 2936 9700
TIME...MOT...LOC 0032Z 250DEG 13KT 2937 9727

PLATT

Special Weather Statement
National Weather Service Austin/San Antonio TX
810 PM CDT Tue May 11 2021

TXZ188>190-120200-
Blanco TX-Gillespie TX-Kendall TX-
810 PM CDT Tue May 11 2021

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN BLANCO...
SOUTHEASTERN GILLESPIE AND NORTHEASTERN KENDALL COUNTIES UNTIL 900 PM
CDT...

At 810 PM CDT, Doppler radar was tracking a strong thunderstorm 7
miles southwest of Albert, or 14 miles west of Blanco, moving
northeast at 15 mph.

Penny size hail will be possible with this storm.

Locations impacted include...
Blanco, Stonewall, Rocky Creek, Flugrath, Hye, Albert, LBJ State Park
and LBJ National Historical Park.

A Severe Thunderstorm Watch remains in effect until 1000 PM CDT for
south central Texas.

LAT...LON 2999 9864 3011 9876 3035 9858 3010 9836
TIME...MOT...LOC 0110Z 232DEG 11KT 3009 9866

PLATT

Special Weather Statement
National Weather Service Austin/San Antonio TX
843 PM CDT Tue May 11 2021

TXZ192-120230-
Travis TX-
843 PM CDT Tue May 11 2021

...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN TRAVIS COUNTY UNTIL
930 PM CDT...

At 842 PM CDT, Doppler radar was tracking a strong thunderstorm near
Cypress Mill, or 12 miles northwest of Dripping Springs, moving
northeast at 25 mph.

Nickel size hail will be possible with this storm.

Locations impacted include...
Austin, Leander, Lakeway, Lago Vista, Hudson Bend, The Hills,
Mansfield Dam, Jonestown, Briarcliff, Point Venture and Volente.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

&&

A Severe Thunderstorm Watch remains in effect until 1000 PM CDT for
south central Texas.

LAT...LON 3043 9781 3029 9808 3036 9817 3046 9810
      3049 9810 3048 9811 3049 9812 3052 9811
      3060 9801
TIME...MOT...LOC 0142Z 229DEG 20KT 3035 9815

PLATT