Flash Flood and Hail in Texas, May 19 to 20, 2023

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
626 PM CDT Fri May 19 2023

...New AVIATION...

.MESOSCALE UPDATE FOR SEVERE THUNDERSTORM WATCH 229
Issued at 341 PM CDT Fri May 19 2023

The forecast remains on track from the short term discussion below.
CI has begun in between the two areas mentioned below, across the
southeastern portion of the SJT CWA. These storms are in a favorable
environment to become severe over the next hour or so with large to
very large hail being the main threat initially, hence the issuance
of the watch. These storms and any storms that make it east of the
Rio Grande may begin to impact the CWA as early as 22z. How quickly
storms congeal and move southeast is a little uncertain, and portions
of the watch area may need to be expanded in time if conditions
warrant later this evening. Severe probabilities according to the
HREF drop off pretty quickly as convection reaches the I-35 corridor
later this evening, which makes sense given increasing convective
inhibition after sunset, but an isolated strong storm or two cannot
be ruled out through Saturday morning.

&&

.SHORT TERM...
(Tonight through Saturday night)
Issued at 208 PM CDT Fri May 19 2023

The main focus of the short term period will be on the storm
potential late this afternoon and through the evening hours across
the region. A cold front currently along a line from just south of
Midland to near Wichita Falls will continue to move south into
tomorrow, likely entering our northern counties late this evening.
Along and ahead of the front, at least scattered thunderstorm
development is expected, with CI already in process across portions
of NE TX. There is a secondary area of thunderstorm development
which is also already in progress across the higher terrain of
Mexico. This activity is more driven by a 500mb shortwave riding
atop a subtropical ridge centered near the Bay of Campeche. Over the
course of the afternoon and evening, both clusters of thunderstorm
development are expected to merge across the CWA. The environment
across south-central Texas is favorable for strong to severe
thunderstorms, with boundary layer temperatures approaching 90
degrees and surface dewpoints generally in the upper 60s to low 70s
contributing to 3000-4000 J/kg of SBCAPE. Additionally, effective
bulk shear is expected to increase into the 30-40 kt range across
the region this afternoon with the approach of the shortwave. This
amount of instability and shear will be plenty sufficient for severe
storms capable of producing large hail and damaging wind gusts.
Relatively weak flow and shear in the lowest levels of the
atmosphere will result in a negligible threat for tornadoes. There
will however be potential for at least isolated instances of
excessive rainfall/flooding as PWATs across the region currently
fall into the 1.3-1.4" range according to the SPC Mesoanalysis Page,
though the HREF shows PWAT values approaching/exceeding 1.8" across
western portions of the CWA this evening/overnight. Due to the
moisture and the potential for some back-building cells along the
front/surface trough, WPC has upgraded to a Slight Risk (Level 2/4)
for portions of the area in their latest Excessive Rainfall Outlook.

Showers and storms will likely be ongoing across the southwestern
half of the CWA post-sunrise tomorrow morning. SPC and WPC both have
a portion of this area under a Marginal Risk in their respective
outlooks after 12Z tomorrow. While an isolated strong to severe
storm cannot be ruled out, in general the expectation is for mainly
sub-severe storms and possibly some isolated nuisance flooding. As
the front gets hung up along the higher terrain of Mexico, chances
for showers and storms will continue across mainly the Rio Grande
Plains through Saturday afternoon. Overnight into Sunday, CAMs
depict this activity beginning to move east as a second shortwave
arrives and helps flatten the ridge some.

While it is technically a cold front, the northerly wind shift will
do little in terms of our temperatures and humidity as is typical
this time of year. Expect a slight drop in both, but with no major
reprieve.

&&

.LONG TERM...
(Sunday through Friday)
Issued at 208 PM CDT Fri May 19 2023

A shortwave will bring some additional light rain chances to the
western half of the area Sunday morning, with most models showing
less activity and a weakening trend into Sunday afternoon. Have
shifted the highest PoPs westward this day with generally dry
conditions for the Coastal Plains and northern I-35 corridor and Hill
Country, although a scattered shower isn't out of the question as
this shortwave shifts east. "Cooler" weather is anticipated Sunday
afternoon with highs mainly in the 80s, a bit cooler in portions of
the Hill Country and southern Edwards Plateau in the 70s.

Dry conditions are expected on Monday as mid-level northwest flow
begins to set up for the week over South-Central Texas. Upper ridging
becomes more amplified by mid-week as we reside between two strong
areas of low pressure to our west and east. Could see a few
shortwaves bring some low end PoPs to our area this upcoming week,
but the better chances remain to the northeast. Still, have some
15-25 percent PoPs in the northeast portion of our area each day
Tuesday through Thursday. In general, would be exact mainly dry and
warm conditions through the work week. By Tuesday, widespread highs
in the upper 80s to low 90s are expected across much of the area with
similar temperatures expected through the week.

&&

.AVIATION...
(00Z TAFS)
Issued at 619 PM CDT Fri May 19 2023

Scattered TSRAs have develop just north and west of the region. Some
of these storms will work into the Hill Country this evening, along
and north of a BMQ-ERV-DRT line. Still uncertainty in the forecast
overnight into early Saturday morning with coverage and placement of
convection as the cold front reaches the area. More favored
locations appear to be along and west of a ERV-SAT line. Otherwise,
MVFR ceilings and north wind developing behind the cold front.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              67  84  65  81 /  40  10  10  10
Austin Bergstrom Intl Airport  68  82  65  78 /  30  10  10  10
New Braunfels Muni Airport     69  84  67  81 /  30  20  10  10
Burnet Muni Airport            64  80  62  79 /  60  10  10  10
Del Rio Intl Airport           71  83  68  83 /  50  50  40  30
Georgetown Muni Airport        66  80  64  79 /  40  10  10  10
Hondo Muni Airport             68  82  66  80 /  70  50  30  20
San Marcos Muni Airport        68  83  66  79 /  30  20  10  10
La Grange - Fayette Regional   70  82  67  79 /  10  10  10  10
San Antonio Intl Airport       70  83  68  80 /  40  30  20  10
Stinson Muni Airport           70  85  69  82 /  40  30  20  10

&&

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

&&

Short-Term...Gale
Long-Term...27
Aviation...76

Hazardous Weather Outlook...UPDATED
National Weather Service Austin/San Antonio TX
333 PM CDT Fri May 19 2023

TXZ171>173-183>194-202>209-217>225-228-202045-
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-
333 PM CDT Fri May 19 2023

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

.DAY ONE...Tonight.

There is a level 2 out of 5 risk for strong to severe storms from
late this afternoon through tonight across the Edwards Plateau,
Hill Country, and I-35 corridor. Large hail and damaging wind
gusts are the main severe threats. In addition, locally heavy
rainfall and isolated flooding is possible. A Severe THunderstorm
Watch is in effect until 10 PM this evening for most of the
locations mentioned above.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

There is a level 1 out of 5 risk for strong to severe storms and
locally heavy rainfall across the Rio Grande Plains on Saturday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not anticipated.