Special Weather Statement, NWS Austin/San Antonio, TX

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
1252 PM CDT Tue May 18 2021

.AVIATION...
VFR conditions have returned to San Antonio and Del Rio and MVFR
ceilings are lingering over AUS. The ceiling should lift to VFR at
AUS within the next hour or two. There is an area of thunderstorms
northwest of San Antonio, but these storms are moving toward the
northeast and should avoid the terminals. Later this afternoon
additional storms will form and move over the Austin and San Antonio
airports. There is a thunderstorm west of DRT and this will likely
move across the airport within the next hour or so. This will lower
visibility and produce some gusty winds. Showers and thunderstorms
will become more numerous tonight and continue into Wednesday.
Ceilings will be dropping to MVFR/IFR with showers and thunderstorms.
We should improve to VFR Wednesday morning.

&&

.PREV DISCUSSION... /ISSUED 303 AM CDT Tue May 18 2021/

SHORT TERM (Today through Wednesday)...
.STRONG TO SEVERE THUNDERSTORMS ALONG WITH FLASH FLOODING APPEAR
LIKELY OVER THE NEXT SEVERAL DAYS...

South-Central Texas will remain within a fairly stormy pattern as
southwesterly flow aloft continues for the foreseeable future. Water
vapor imagery shows an H5 low centered over south-central Colorado
as of 07Z. This upper low will continue to slowly slide eastward,
before becoming an open wave by 00Z Thursday over western Kansas. A
series of mid-level shortwaves will continue to orbit the periphery
of this upper low, resulting in several rounds of strong to severe
thunderstorms capable of large hail, damaging winds, and most
concerning of all, heavy rains and flash flooding.

For the near term and the rest of tonight, convection remains
possible, especially over the Rio Grande Plains and Southern Edwards
Plateau, but a rather stout cap around 700 mb, with temps of 10 to
12 C appears to be squashing any sort of convection that attempts to
develop. This will likely continue through early morning in the
absence of a meaningful mid-level lifting mechanism, which is
currently sparking off convection near the Midland-Odessa area. A
stronger shortwave looks to round the base of the trough and eject
out over the western Hill Country and Southern Edwards Plateau by
mid to late Tuesday morning, which will be our next trigger for
possible storm development by late Tuesday morning/early afternoon.
With deep layer shear of 40-50 kts, MLCAPE of 2500-3500 J/kg, and
mid level lapse rates still on the order of 7-7.5 C/km, any storms
that form could become strong to severe with large hail and damaging
wind gusts. Flash flooding will become a bigger concern toward
Tuesday evening, especially if storms can organize and grow into
clusters or an MCS. PWATs of 1.5-2" will be common, with rainfall
rates of 1-2" per hour or higher within the heaviest storms. The
forecast still remains fairly complicated due to convective
processes that are harder to pinpoint in a setup like this.
Something to note: the WPC Excessive Rainfall Outlook for day 1 puts
the entire I-35 corridor including the San Antonio Metro within a
slight risk, along with portions of Williamson and Lee County within
a moderate risk for flash flooding. Rainfall totals of 1-2" with
isolated higher totals in excess of 3" are possible over the I-35
corridor and Coastal Plains.

Our next possible round of storms looks to arrive sometime late
Tuesday evening or early Wednesday morning, but exactly where storms
form is the biggest question. Another mid-level shortwave may move
through South-Central Texas late Tuesday evening through early
Wednesday morning, with thunderstorms attempting to organize over
central Texas and then push southeastward, forming into a complex by
very early Wednesday morning. The 06Z HRRR is very concerning in
it's depiction of a complex organizing and moving through the Hill
Country, then I-35 corridor by sunrise Wednesday. Very heavy rainfall
which could lead to flash flooding is expected during the day
Wednesday. Training of storms and slow storm movement will likely
result in flooding rather quickly, especially for areas that have
already seen heavy rainfall over the last few days. The day 2 ERO
places the entire I-35 corridor including the Austin and San Antonio
Metros within a moderate risk for flash flooding. Rainfall totals of
2-5" with isolated totals greater than 6" are possible on Wednesday
alone if latest guidance comes to fruition. A flash flood watch is in
effect for the eastern 2/3rds of our CWA through 18Z Thursday, with
rainfall totals of 3-7" and isolated totals up to 10" possible.

LONG TERM (Wednesday Night through Monday)...
The pattern aloft over the CONUS will be dominated by an upper level
ridge over the southeastern states mid to late week that drifts to
the Mississippi Valley over the weekend with an upper level trough
centered over the Great Basin mid week through the weekend. Closer
to our area, an upper level low develops over southern Texas into
northeastern Mexico mid to late week, then gets stretched and weakens
over the weekend. An unseasonably moist airmass remains, especially
over our eastern areas due to an upper level flow from the western
Caribbean and a lower level flow from the Gulf of Mexico. Strong
upward forcing of this unseasonably moist airmass will allow for
more rounds of mainly diurnally driven showers and thunderstorms
especially over our eastern areas along with a threat of locally
heavy rains and additional flooding. There is also a possibility of
a few strong to perhaps severe storms due to MUCAPE of 500 to 1500
J/kg. Temperatures will average below normal due to the extensive
cloudiness and areas of rain.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              69  77  66  80  69 /  80  90  70  60  40
Austin Bergstrom Intl Airport  68  78  65  80  68 /  80  90  70  60  40
New Braunfels Muni Airport     69  78  66  82  69 /  60  90  60  50  30
Burnet Muni Airport            66  75  64  79  66 /  70  80  50  40  30
Del Rio Intl Airport           70  83  67  87  70 /  30  50  10  -   10
Georgetown Muni Airport        67  75  65  79  68 /  80  90  70  60  40
Hondo Muni Airport             69  79  64  83  68 /  50  90  40  30  20
San Marcos Muni Airport        68  78  65  81  68 /  70  90  60  50  30
La Grange - Fayette Regional   73  80  68  81  71 /  70 100  80  70  40
San Antonio Intl Airport       69  77  66  81  69 /  50  90  50  40  30
Stinson Muni Airport           71  79  67  82  69 /  50  90  50  40  30

&&

.EWX WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch through Thursday afternoon for Atascosa-Bandera-
Bastrop-Bexar-Blanco-Burnet-Caldwell-Comal-De Witt-Fayette-Frio-
Gillespie-Gonzales-Guadalupe-Hays-Karnes-Kendall-Kerr-Lavaca-Lee-
Llano-Medina-Travis-Williamson-Wilson.

&&

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

Hazardous Weather Outlook
National Weather Service Austin/San Antonio TX
354 AM CDT Tue May 18 2021

TXZ171>173-183>194-202>209-217>225-228-190900-
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-
354 AM CDT Tue May 18 2021

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

.DAY ONE...Today And Tonight.

Strong to severe thunderstorms are expected this afternoon and
evening, with large hail and damaging winds possible. Very heavy
rainfall is expected with any storms that form. All of South-
Central Texas is within a Slight Risk (Level 2 of 5) for severe
storms Tuesday afternoon and evening.

A flash flood watch is also in effect for the eastern half of
South-Central Texas...or along and east of a line from Mountain
Home to Dilley. The heavy rain threat will greatly increase this
evening as storms organize out west and move through the region
late tonight.

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

Several rounds of showers and thunderstorms are possible through
the week, especially Wednesday through Thursday. Thunderstorms
could be strong to severe at times, and there is a Marginal Risk
(Level 1 of 5) for severe storms Wednesday for most of South-
Central Texas.

A flash flood watch is in effect east of a Mountain Home to
Dilley line through 1 PM CDT Thursday. Daily rainfall amounts of
1 to 4 inches are possible, and portions of Central Texas could
end up with multiple day rainfall totals up to 10 inches. These
heavy rainfall totals will likely send some area rivers and
streams into minor or moderate flood stages.

.SPOTTER INFORMATION STATEMENT...

Spotters are encouraged to report severe weather and/or flash flooding
to the National Weather Service.

Special Weather Statement
National Weather Service Austin/San Antonio TX
1029 AM CDT Tue May 18 2021

TXZ185-186-188-181615-
Gillespie TX-Kerr TX-Real TX-
1029 AM CDT Tue May 18 2021

...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN KERR AND WEST
CENTRAL GILLESPIE COUNTIES UNTIL 1115 AM CDT...

At 1028 AM CDT, Doppler radar was tracking a strong thunderstorm 8
miles southwest of Kerr Wildlife Management Area, or 20 miles north
of Vanderpool, moving northeast at 45 mph.

Penny size hail and winds in excess of 40 mph will be possible with
this storm.

Locations impacted include...
Mountain Home, Kerr Wildlife Management Area, Harper, I-10 Near The
Kimble-Kerr County Line and The Intersection Of I-10 And Us 290.

LAT...LON 3030 9921 2991 9958 3001 9976 3029 9960
      3029 9930 3034 9930
TIME...MOT...LOC 1528Z 213DEG 39KT 3003 9963

MO

Special Weather Statement
National Weather Service Austin/San Antonio TX
1135 AM CDT Tue May 18 2021

TXZ184>186-181730-
Kerr TX-Edwards TX-Real TX-
1135 AM CDT Tue May 18 2021

...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN KERR...EASTERN
EDWARDS AND NORTHWESTERN REAL COUNTIES UNTIL 1230 PM CDT...

At 1135 AM CDT, Doppler radar was tracking a strong thunderstorm near
Vance, or 13 miles southeast of Rocksprings, moving northeast at 35
mph.

Penny size hail and winds in excess of 40 mph will be possible with
this storm.

Locations impacted include...
Barksdale, Vance, Us-83 Near The Kerr-Kimble County Line, I-
10 Near The Kimble-Kerr County Line, The Intersection Of I-
10 And Us 290, Us-377 Near The Kimble-
Edwards County Line, Devil's Sinkhole State Natural Area and Prade
Ranch.

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.

&&

LAT...LON 3029 9939 2971 10004 2990 10030 3029 9996
TIME...MOT...LOC 1635Z 210DEG 33KT 2985 10010

MO

Special Weather Statement
National Weather Service Austin/San Antonio TX
1254 PM CDT Tue May 18 2021

TXZ186>189-204-181845-
Gillespie TX-Kerr TX-Medina TX-Bandera TX-Kendall TX-
1254 PM CDT Tue May 18 2021

...SIGNIFICANT WEATHER ADVISORY FOR NORTH CENTRAL MEDINA...CENTRAL
BANDERA...SOUTHEASTERN KERR...WESTERN GILLESPIE AND WESTERN KENDALL
COUNTIES UNTIL 145 PM CDT...

At 1253 PM CDT, Doppler radar was tracking strong thunderstorms along
a line extending from Kerrville-Schreiner Park to near Lakehills.
Movement was northeast at 45 mph.

Penny size hail and wind gusts up to 50 mph will be possible with
these storms.

Locations impacted include...
Medina, Kerrville, Boerne, Fredericksburg, Comfort, Bandera, Ingram,
Walnut Grove, Camp Verde, Bandera Falls, Tivydale,
Kerrville-Schreiner Park, Rocky Hill, Waltonia, Sisterdale, Pipe
Creek, Welfare, Nelson City, Center Point and Waring.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

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

These storms 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.

&&

LAT...LON 2993 9862 2944 9914 3000 9937 3050 9894
      3050 9888
TIME...MOT...LOC 1753Z 219DEG 37KT 2999 9912 2963 9899

MO

Special Weather Statement
National Weather Service Austin/San Antonio TX
129 PM CDT Tue May 18 2021

TXZ171-186>190-204>206-181915-
Comal TX-Bexar TX-Blanco TX-Gillespie TX-Kerr TX-Llano TX-Medina TX-
Bandera TX-Kendall TX-
129 PM CDT Tue May 18 2021

...SIGNIFICANT WEATHER ADVISORY FOR EASTERN MEDINA...SOUTHEASTERN
BANDERA...SOUTHEASTERN KERR...BLANCO...EASTERN GILLESPIE...EASTERN
LLANO...KENDALL...NORTHWESTERN BEXAR AND NORTHWESTERN COMAL COUNTIES
UNTIL 215 PM CDT...

At 128 PM CDT, Doppler radar was tracking strong thunderstorms along
a line extending from near Cain City to near Walnut Grove to near
Government Canyon State Natural Area. Movement was northeast at 50
mph.

Nickel size hail and wind gusts up to 50 mph will be possible with
these storms.

Locations impacted include...
Boerne, Fredericksburg, Kingsland, Comfort, Blanco, Round Mountain,
Gainesville, Fair Oaks Ranch, Granite Shoals, Horseshoe Bay, Cross
Mountain, Johnson City, Buchanan Lake Village, Stonewall, Guadalupe
River State Park, Kendalia, Bluffton, Rocky Hill, Kreutzberg and
Blumenthal.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

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

&&

LAT...LON 3092 9846 3068 9842 3067 9844 3062 9841
      3057 9841 3056 9840 3002 9831 2948 9884
      2965 9895 3011 9898
TIME...MOT...LOC 1828Z 207DEG 46KT 3020 9886 2990 9873 2962 9883

MO

Special Weather Statement
National Weather Service Austin/San Antonio TX
238 PM CDT Tue May 18 2021

TXZ190-191-205>207-182045-
Guadalupe TX-Comal TX-Bexar TX-Blanco TX-Hays TX-
238 PM CDT Tue May 18 2021

...SIGNIFICANT WEATHER ADVISORY FOR WESTERN HAYS...WEST CENTRAL
GUADALUPE...SOUTHEASTERN BLANCO...NORTHEASTERN BEXAR AND COMAL
COUNTIES UNTIL 345 PM CDT...

At 238 PM CDT, Doppler radar was tracking strong thunderstorms along
a line extending from Blanco to Smithson Valley to Hollywood Park.
Movement was northeast at 20 mph.

Penny size hail and wind gusts up to 50 mph will be possible with
these storms.

Locations impacted include...
San Antonio, New Braunfels, Schertz, Cibolo, Universal City, Live
Oak, Selma, Dripping Springs, Wimberley, Blanco, San Antonio Int
Airport, Canyon Lake Dam, Randolph AFB, Canyon Lake, Alamo Heights,
Windcrest, Bulverde, Garden Ridge, Hollywood Park and Olmos Park.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

&&

A Tornado Watch remains in effect until 900 PM CDT for south central
Texas.

LAT...LON 3003 9801 2958 9808 2946 9857 2978 9842
      2991 9844 2994 9842 2999 9846 3011 9848
      3029 9807
TIME...MOT...LOC 1938Z 234DEG 19KT 3009 9840 2983 9836 2957 9847

MO

Special Weather Statement
National Weather Service Austin/San Antonio TX
304 PM CDT Tue May 18 2021

TXZ207-221-182045-
Guadalupe TX-Wilson TX-
304 PM CDT Tue May 18 2021

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN GUADALUPE AND NORTH
CENTRAL WILSON COUNTIES UNTIL 345 PM CDT...

At 302 PM CDT, Doppler radar was tracking a strong thunderstorm near
Sutherland Springs, or near Floresville, moving north at 20 mph.

Nickel size hail and wind gusts up to 50 mph will be possible with
this storm.

Locations impacted include...
Stockdale, La Vernia, New Berlin, Sutherland Springs and Zuehl.

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.

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 Tornado Watch remains in effect until 900 PM CDT for south central
Texas.

LAT...LON 2917 9817 2940 9817 2944 9814 2945 9812
      2948 9812 2948 9813 2949 9814 2948 9816
      2950 9817 2946 9784 2915 9800
TIME...MOT...LOC 2002Z 189DEG 17KT 2921 9809

PLATT