Flash Flood Warning 29, NWS Austin/San Antonio, TX

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
927 PM CDT Fri Sep 2 2022

...New UPDATE...

.UPDATE...
Issued at 918 PM CDT Fri Sep 2 2022

Radar trends and the latest hi-res model guidance generally keep rain
chances highest through this evening and into the overnight hours
across the southern Edwards Plateau and into portions of the nearby
Hill Country. Farther east, rain chances do not appear as favorable
and we have either greatly reduced or removed rain chances for most
areas along and east of I-35. Otherwise, only minor changes were made
to the hourly temperature, dewpoint and wind grids to better align
with current observations.

&&

.SHORT TERM...
(Tonight through Saturday night)
Issued at 211 PM CDT Fri Sep 2 2022

An upper level trough extends from the northern plains to central
Texas this afternoon. A surface trough extends from southeastern
Oklahoma to west Texas near Midland. This boundary is the focus of
convection this afternoon. There is also convection developing along
the seabreeze over the Coastal Plains. The seabreeze activity will
move up toward our Coastal Plains, but should dissipate as the sun
goes down. The surface boundary north of our CWA will move slowly
southward and should lead to more long lived showers and
thunderstorms. We will carry higher PoPs over the north and west as
this boundary drifts toward us. PW values remain 1.5-2.1 inches
across the CWA and locally heavy rain is possible with stronger
storms tonight. WPC has most of our CWA in a marginal risk for
excessive rainfall tonight.

For Saturday, the weak boundary should be near our CWA and the upper
trough will dip farther south into the region as well. This should
allow for scattered to numerous showers to develop during the
afternoon. PoPs are in the 60%-80% range. PW values near 2-2.2" will
continue the threat of locally heavy rainfall. But with lack of
clear focus, it is tough to know where exactly the higher rainfall
amounts will be located. WPC has a slight risk of excessive rainfall
for Saturday and a Flood Watch could be issued at a later time if
confidence increases on a particular location seeing the heavier
rainfall that could lead to flash flooding. The clouds and rain will
keep temperatures down below normal with highs from the lower 80s to
the lower 90s.

Saturday night rain chances will continue to shift to the south.
Higher PoPs will be over the southern half of our CWA. The airmass
will still be very moist and locally heavy rain will be possible.

&&

.LONG TERM...
(Sunday through Friday)
Issued at 211 PM CDT Fri Sep 2 2022

The main energy from the Central US upper trough sends the deeper
convection south of Hwy 90 by Sunday morning as post-frontal air
looks to keep the cooler trend of max temperatures in place. Lowest
maxes Sunday through be over the southern counties where light
overrunning showers and isolated storms may continue. The Tech WRF
also some elevated activity developing farther north Sunday
afternoon, and the medium range models have a southward moving
shortwave on the back side of the upper trough to help with this
convection. We'd think this secondary round of activity would be in a
less tropical environment, so the potential for run-off concerns
might just be in a few isolated spots that had heavy rains the day
before. With Saturday potentially unleashing the highest rain totals
for the next few days, we'd be hesitant to say the excessive run-off
concerns will abate for Sunday at this time.

The Sunday shortwave looks to cut southwest of the forecast area to
continue a fetch of pooled Pacific and Gulf moisture over the Coastal
Plains leaving us with another day of high rain chances Monday and
below normal temps with mostly cloudy skies, and a stagnant upper
troughing pattern that's hung up over the region.

The National Hurricane Center shows a high chance of tropical
cyclone formation and a possible cyclone track hugging close to the
Pacific coast of Mexico early next week. This system may continue
to feed moisture and instability over the Mexican plateau and into
the SW side of the stubborn Central US upper trough, keeping over
South Central TX high rain chances, temperatures cooler than normal,
and unfortunately poor weather predictability due to the broad nature
of this upper pattern. There could be a long period of frontal
overrunning or the frontal forcing could retreat north and open the
area up to a deeper moisture and heavy rainfall threat. With out much
confidence in the medium range our main focus for messaging will be
over the next 2-3 days.

&&

.AVIATION...
(00Z TAFS)
Issued at 650 PM CDT Fri Sep 2 2022

Isolated convection continues to develop over the Hill Country, with
another area noted east of I-35 into the Highway 77 corridor. We will
continue to mention VCSH at AUS for the next few hours, but leave any
mention out of the remainder of our TAF sites through this evening.
Models and radar trends suggest some light showers may develop near
DRT as activity currently over the lower Trans Pecos may help
initiate a few showers overnight. Chances for convection will
increase by late morning near AUS, with SAT,SSF and DRT seeing better
chances by mid-afternoon. An outflow boundary or weak front will
progress southward and help initiate new convection. For now, we
have gone with TEMPO groups at all sites for the afternoon into early
evening hours.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              76  87  73  88 /  20  70  30  50
Austin Bergstrom Intl Airport  74  86  73  89 /  20  70  30  50
New Braunfels Muni Airport     75  88  72  88 /  20  70  40  60
Burnet Muni Airport            73  85  71  90 /  30  70  20  40
Del Rio Intl Airport           75  86  73  85 /  50  80  60  60
Georgetown Muni Airport        74  85  71  90 /  30  70  20  40
Hondo Muni Airport             76  89  73  85 /  40  80  50  70
San Marcos Muni Airport        74  87  71  89 /  20  70  40  60
La Grange - Fayette Regional   74  87  73  88 /  20  80  40  60
San Antonio Intl Airport       76  89  74  85 /  30  70  50  70
Stinson Muni Airport           76  90  74  86 /  20  80  50  70

&&

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

Short-Term...Platt
Long-Term...Morris
Aviation...Platt

Hazardous Weather Outlook
National Weather Service Austin/San Antonio TX
412 AM CDT Fri Sep 2 2022

TXZ171>173-183>194-202>209-217>225-228-031200-
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-
412 AM CDT Fri Sep 2 2022

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

.DAY ONE...Today And Tonight.

Isolated to widely scattered showers and thunderstorms are
possible this afternoon and evening. A few storms could produce
heavy rainfall that leads to localized flooding.

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

Scattered to numerous showers and thunderstorms remain possible
each day into and through the upcoming Labor Day weekend. Some
storms could produce heavy rainfall that leads to localized
flooding.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not anticipated.