225
FXUS64 KEWX 290601
AFDEWX

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
101 AM CDT Tue Sep 29 2026

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

.KEY MESSAGES...
Updated at 1225 AM CDT Tue Sep 29 2026

- Continued above normal temperatures through Wednesday across all
  of South Central Texas.

- An active pattern will take shape mid to late week, with
  concerns for heavy rainfall and flooding on the increase,
  especially Thursday into Friday.

&&

.SHORT TERM...
(Today through Wednesday)
Issued at 1225 AM CDT Tue Sep 29 2026

Some lingering northwest flow aloft was enough to aid in the
development of a few showers across the southern Edwards Plateau
region yesterday afternoon. Radar estimated a small area of 1/4" to
3/4" in northern Edwards County. Some showers also managed to
develop over the coastal plains region with southern Fayette and
northern Lavaca showing a few spots of 1/2" to near 1.25".

For today, we will see an increase in southeasterly low-level flow
due to lee-side surface troughing over the plains of eastern CO, as
well as the remnant low-level circulation from `Polo` emerging over
far west Texas later today. Widespread low clouds will be in place
this morning, with some slow clearing of clouds in the afternoon.
Temperatures will be above normal, with highs ranging from near 90
to near 100 degrees. Heat index values may briefly approach 108
degrees in the coastal plains, with peak readings closer to 105
degrees along I-35. With the increase in low-level moisture and
onset of daytime heating, some isolated to scattered convection will
develop from the coastal plains region northward into the I-35
corridor. As we head into the evening and overnight hours, we will
continue to see a steady, low-level flow from from the southeast
along with mid and upper level moisture increasing from the west in
advance of an upper low. This should result in the higher rain
chances confined to the western portions of Val Verde County. There
is a level 1 of 4 risk for locally heavy rainfall across the far
western portion of Val Verde County late Tuesday into early
Wednesday.

The weather pattern on Wednesday will begin to change as an
approaching upper low over the southwestern U.S. weakens the
subtropical ridge axis over Texas and the western Gulf. An increase
in southwest flow aloft combined with deep moisture will help
generate some isolated to scattered convection during the daytime
hours. While we do expect to see another round of high temperatures
in the upper 80s to upper 90s, a good amount of cloud cover is
anticipated and we could be a little high with our current forecast
numbers.

&&

.LONG TERM...
(Wednesday night through Monday)
Issued at 1225 AM CDT Tue Sep 29 2026

We expect to see an increase in the coverage of precipitation
Wednesday night beginning out west across the Rio Grande plains as
a Pacific front slowly moves in from the west. Plenty of moisture
will be in place ahead of this feature as precipitable water
values likely climb to around 2" for most areas. WPC continues to
show a level 2 of 4 risk for flooding generally along and north of
a Del Rio to Austin line, with a level 1 of 4 risk farther east
through most of the I-35 corridor.

On Thursday, rain chances will increase significantly across the
region as the Pacific front and upper level trough axis approach
from the west. The medium range models hint at a southwest to
northeast oriented line of convection developing early across the
southern Edwards Plateau and northern Hill Country, with convection
expected to expand slowly eastward during the day as peak heating is
realized. With the Pacific front, well above normal moisture and
upper level trough axis, heavy rainfall is likely to develop across
a good portion of the region Thursday and into Thursday night. The
WPC continues to show a level 2 of 4 risk in place across south
central Texas, with a level 3 of 4 over the Hill Country and I-35
corridor.

Rain chances remain high into Friday, but much will depend on the
speed of the Pacific cold front. The tail end of the NAM shows the
front pushing southward into the coastal plains early Friday
morning, which would help shift the focus for heavy rainfall a
little farther to the east. The ECMWF and GFS ensembles as well as
their AI runs are starting to show some of the heavier precipitation
amounts across portions of the Rio Grande plains between Del Rio and
San Antonio, northward into the Hill Country. We are still early in
this event and as the hi-res members start to pick up on this,
additional changes to the forecast are likely. We will certainly
need to watch Thursday, Thursday night and even into early Friday
morning as models are favoring this time period for the higher
rainfall amounts. We could see some widespread rainfall amounts of 2
to 4 inches with local amounts up to 8 inches on Thursday into
Friday.

For the upcoming weekend, some remnant upper level energy may hang
back to our west as `Rachel` continues in the eastern Pacific. While
our western areas may see slightly lower moisture levels, we will
still have plenty of moisture to work with farther east into the I-
35 corridor and coastal plains. Rain chances will remain in the
forecast for the weekend into Monday. With good precipitation
chances, northerly winds in the lower levels and cloud cover, highs
will generally range from the mid 70s to the lower 80s along with
overnight lows in the 60s.

&&

.AVIATION...
(06Z TAFS)
Issued at 100 AM CDT Tue Sep 29 2026

Falling heights over the western CONUS and monsoonal instability
over the W TX/NM with tropical ties to TC Polo will send the
onshore windspeeds upward over the next 24 hours. This is already
showing up in the overnight low cloud return over the I-35
Corridor with the Satellite Nighttime Microphysics product picking
up on the clouds before 05Z. The latest frames show the pockets of
low CIGs in between AUS and SAT, so we`ll hold off adding the low
CIG period until 07Z. We have DRT getting the CIGs by 11Z as the
areas of clouds seen on satellite will have a lot of ground to
cover to spread that far west. The winds should get gusty during
the daytime, so we`ll opt for a summer-like mix out to VFR skies
by around 16Z at all TAF sites. There is a mixed bag of solutions
for what might develop in the strong onshore flow for this
afternoon in terms of convection chances, so we`ll hold off any
mention of convection for the I-35 sites until we can get a better
look at some more rapid refresh solutions. Then, with even higher
moisture content in the low levels, we`d expect to see the low
CIGs arrive into I-35 by 05Z if not earlier.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              75  97  75  91 /  20  50  70 100
Austin Bergstrom Intl Airport  74  97  75  91 /  20  50  70 100
New Braunfels Muni Airport     74  96  74  90 /  30  50  70 100
Burnet Muni Airport            73  93  73  85 /  20  40  70 100
Del Rio Intl Airport           77  98  73  89 /  40  20  90  80
Georgetown Muni Airport        74  96  74  89 /  10  50  70 100
Hondo Muni Airport             74  96  74  87 /  20  30  80 100
San Marcos Muni Airport        73  97  74  91 /  30  50  70 100
La Grange - Fayette Regional   75  97  76  94 /  20  40  40  90
San Antonio Intl Airport       76  95  76  88 /  30  40  80 100
Stinson Muni Airport           77  97  77  90 /  30  40  70 100

&&

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

$$

SHORT TERM...Platt
LONG TERM....Platt
AVIATION...18