Severe Thunderstorm Warning 115, NWS Austin/San Antonio, TX

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
303 PM CDT Thu May 21 2026

...New SHORT TERM, LONG TERM...

.KEY MESSAGES...

- Low to medium chances for rain this afternoon/evening. Isolated
  showers and storms may develop with the most favored areas over
  the southern Edwards Plateau, Rio Grande, and parts of the Hill
  Country.

- Flood Watch Friday evening through Monday evening for areas
  along and east of a Kerr to Frio County line.

- Active and unsettled weather pattern continues into next week.
  Multiple rounds of storms with heavy rain are possible and could
  lead to localized flooding.

&&

.SHORT TERM...
(Tonight through Friday night)
Issued at 301 PM CDT Thu May 21 2026

A stalled frontal boundary along with previous outflow boundaries
will be the main focus for additional thunderstorm development late
this afternoon into tonight. Many areas did not receive much in the
way of showers and thunderstorms last night which leads to a rather
challenging and low confidence forecast for the short term portion.
That being said we are starting to see clouds clearing in the
western half of the area when looking at visible satellite imagery
leading to the possibility of convection to form as the atmosphere
begins to destabilize. SPC also has this area in a level 1 of 5 risk
for severe weather with the main threats being large hail and
damaging wind gusts. We are not anticipating a widespread event
initially this evening but rather a more scattered to isolated
scenario.

Hi-Res models continue to be all over the place regarding
initial placement and timing but the overall consensus is that most
would see activity occur after 4 PM and continue through this
evening into the overnight. An initial round of activity already
located over Llano, Kimble and Mason counties will continue to
progress eastward with activity continuing to form back behind it.
The recent run of RRFS (18Z) shows this complex of activity slowly
drifting southeastward and impacting parts of the Hill Country. The
latest 18Z ACAR sounding at SAT shows MUCAPE of 1800 J/kg while the
AUS sounding shows around 1600 J/kg and along with SPC meso showing
mid-level lapse rates of 6.5 to 7 c/km. Any storms that do form will
have the potential to produce damaging winds, large hail and
torrential rainfall as moisture remains extremely high over the
region. WPC has expanded their level 1 of 4 risk to include the
entire area for today due to the recent rainfall and the anomalously
high moisture located over our area.

Several short range models show a secondary wave of activity forming
over either West TX or Central TX as a another disturbance
progresses eastward. This convection would then swing southward
through the Rio Grande and Southern Edwards Plateau, possibly
clipping portions of Bexar County and perhaps parts of the western
Hill Country. However it should be weakening as it does so with most
activity ending before daybreak Friday morning with most activity
then pushing southward into South TX.

Friday into Friday evening we seem to be in a bit of a lull as we
remain trapped between two disturbances with the one moving off to
our east and then the next one located over West TX and impacting
portions of our western areas beginning as early as Saturday morning.

Additionally due to the area receiving widespread rainfall of 1 to 3
inches over the past 3 days and the potential for additional rounds
of heavy rainfall we went ahead and issued a Flood Watch for the
entirety of the holiday weekend for areas along and east of a Kerr
to Frio county line.

&&

.LONG TERM...
(Saturday through next Thursday)
Issued at 301 PM CDT Thu May 21 2026

As alluded to above, Saturday could shape up to be a very active day
as our next disturbance will be approaching the area sparking
another round of showers and thunderstorms capable of very heavy
rainfall as moisture continues to remain high across the area. There
is relative good agreement on the latest model consensus regarding
the evolution of a low pushing across our area and stalling over
East TX. This low will be the focus for the repeated rounds of
thunderstorms and heavy rainfall over the extended weekend. Many
areas could see a widespread swath of 2 to 4 inches with some areas
seeing isolated totals of up to 6 inches of rainfall especially for
those across the Watch area. As such, WPC currently has our area in
a level 2 of 4 risk for excessive rainfall for areas along and east
of the I-10 to I-35 Corridor including the San Antonio and Austin
Metro areas.

Global models continue to indicate this low meandering somewhere
across East TX until at least Tuesday as the upper level pattern
shows another trough digging down into the Western U.S. This trough
will help to finally kick out the meandering low but also puts our
area back into southwest flow aloft. This then opens the door for
renewed rainfall chances as disturbances continue to push across our
area into next week.

As stated previously this is a rather low confidence and challenging
forecast as each round of storms moves across parts of our area,
more stable conditions will likely follow leading to periods of dry
weather as the atmosphere recharges. Even though many chances for
precipitation are seen in the extended forecast, periods of dry
weather are also expected. Similarly, as each day evolves, the
outflow and leftover boundaries from the previous day's convection
will be the continued focus for renewed development for the next
day. Thus it wont be until 24 to perhaps 48 hrs prior to each day
that we will be able to pinpoint the location and eventually
trajectory of where storms may fire.

It should be noted that every rain event that occurs will continue
to bring soils closer to saturation thus increasing the potential
for excessive run off which can lead to flash flooding or river
flooding. Please continue to monitor the forecast and always have a
way to receive warning information.

&&

.AVIATION...
(18Z TAFS)
Issued at 1235 PM CDT Thu May 21 2026

MVFR cigs are forecast for the next few hours for the San Antonio
and Austin area terminals. Then VFR category is projected to
remain through the rest of the afternoon into the evening. There
is a chance for showers and storms along the Rio Grande Plains
late this afternoon and evening. With that said, included a PROB30
group for KDRT late afternoon into the evening for the
possibility of thunderstorms. A light east to southeast flow is
forecast through the forecast period. MVFR conditions return for
the I-35 airports overnight into Friday morning.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              69  88  72  84 /  30  20  20  90
Austin Bergstrom Intl Airport  68  87  71  83 /  30  20  20  90
New Braunfels Muni Airport     67  86  70  83 /  30  20  20  90
Burnet Muni Airport            66  85  69  81 /  30  20  30  90
Del Rio Intl Airport           67  89  70  85 /  30   0  40  50
Georgetown Muni Airport        67  86  70  82 /  30  10  30  90
Hondo Muni Airport             66  85  69  81 /  30  10  50  90
San Marcos Muni Airport        68  87  71  83 /  30  20  20  90
La Grange - Fayette Regional   69  86  72  83 /  30  30  20  90
San Antonio Intl Airport       69  87  72  83 /  30  20  30  90
Stinson Muni Airport           69  87  72  83 /  30  20  30  90

&&

.EWX WATCHES/WARNINGS/ADVISORIES...
Flood Watch from Friday evening through Monday evening for
TXZ171>173-186>194-204>209-219>225.

&&

SHORT TERM...CJM
LONG TERM....CJM
AVIATION...17

Special Weather Statement
National Weather Service Austin/San Antonio TX
410 PM CDT Thu May 21 2026

TXZ171-188-212200-
Gillespie TX-Llano TX-
410 PM CDT Thu May 21 2026

...A strong thunderstorm will impact portions of northwestern
Gillespie and southwestern Llano Counties through 500 PM CDT...

At 410 PM CDT, Doppler radar was tracking a strong thunderstorm 7
miles southwest of Hilda, or 14 miles south of Mason, moving east at
30 mph.

HAZARD...Winds in excess of 40 mph and penny size 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...
Castell, Cherry Spring, Prairie Mountain, Doss, Enchanted Rock State
Natural Area, and Harper.

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 3070 9872 3030 9893 3040 9930 3050 9931
      3050 9896 3070 9896
TIME...MOT...LOC 2110Z 279DEG 24KT 3053 9922

MAX HAIL SIZE...0.75 IN
MAX WIND GUST...40 MPH

MM