Flood Watch 2, NWS Austin/San Antonio, TX

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
1236 PM CDT Mon Aug 15 2022

...New AVIATION...

.UPDATE...
Issued at 623 AM CDT Mon Aug 15 2022

Updated POPs to reflect current radar trends across the region. An
outflow is moving north from San Marcos and could possibly produce a
stray shower into areas that was expected to remain rain free this
morning. The rain shield with few embedded lightning strikes within
the heaviest mesoscale banding will gradually shift westward this
morning and into the afternoon as the weak surface low continues to
advance more inland across northern Mexico. This means activity will
eventually become more spotty and scattered around the San Antonio
metro area before becoming more isolated for the afternoon. Activity
will continue for our western areas, especially across the Winter
Garden region and along the Rio Grande. Latest convective allowing
models continue to support potential for a few inches of rain across
this region with heavier activity as we go through the day. Minor
flooding continues to be possibility, especially across those areas.

&&

.SHORT TERM...
(Today through Tuesday)
Issued at 327 AM CDT Mon Aug 15 2022

The weak surface low has now moved to the west of the Rio Grande
around Laredo and will continue west-northwestward across the Mexico
states of Nuevo Leon and Coahuila through Monday into Tuesday. The
greatest concerns from overnight through Monday morning will be
pockets of heavy rainfall embedded with any banding across our
western zones, especially across the Winter Garden region and along
the Rio Grande. This region is where the best deep layer moisture
convergence flux and PWATS in the 2 to 2.5 inch range align. The 00Z
deterministic and HREF probability matched mean guidance shows a
solid widespread swath of 1 to 3 inches for the Winter Garden region
with locally higher amounts. Hourly rainfall rates could be as high
as 1 to 3 inches at times underneath the heaviest convection. The
higher rainfall rates could result in some isolated flooding despite
the antecedent very dry soils. Several of the HREF members show that
some banding could continue to extend out to the I-10/37 corridor,
including Bexar County and San Antonio into Monday afternoon. To the
east, including the Austin metro area, conditions are expected to
primarily remain dry. In addition to the sharp gradient on rain
chances, there will also be a large contrast in temperatures across
the region on Monday. Underneath the rain and overcast skies, expect
temperatures to only top out in the low to mid 80s while locations
farther east under a few breaks of sunshine should climb into the
mid to upper 90s. Rain chances are expected to decline into Monday
night with any lingering rain chances becoming confined to locations
along the Rio Grande. Overnight lows fall into the low to mid 70s
while a few locations in the Hill Country may dip just below 70
degrees.

Mid-level 500 mb heights gradually start to rise in the wake of the
low pressure system across northern Mexico on Tuesday. Subsidence
with the rising 500 mb heights will lead to a drier and warmer day
where PWATS fall back into the 1.5 to 1.8 inch range. Most will not
see rain on Tuesday with only low chances lingering along the Rio
Grande. Temperatures generally will trend in the low to mid 90s out
west with mid to upper 90s elsewhere with a few locations reaching
or topping 100 degrees.

&&

.LONG TERM...
(Tuesday night through Sunday)
Issued at 327 AM CDT Mon Aug 15 2022

The presence of the mid-level subtropical ridge axis will result in a
dry and warm day across south central Texas on Wednesday. Some
lingering cloud cover along with anticipated rains from today over
the Rio Grande plains may actually keep high temperatures down in the
mid 90s. Elsewhere, it will be hot with highs in the mid 90s to near
104 degrees. The heat and humidity may produce some heat index values
near Heat Advisory thresholds Wednesday afternoon generally along and
east of the I-35 corridor. We will continue to monitor, but will not
issue and heat headlines at this time.

A change in the mid-level pattern begins to take shape for the latter
half of this week. Northwest flow aloft associated with a large upper
trough over the eastern half of the lower 48 will take shape across
most of Texas. The medium range models continue to remain consistent
in showing a weak cold front moving into the region on Thursday. Some
minor cooling behind the front will be realized over the Hill
Country. However, the front will likely not have too much of an
impact on temperatures elsewhere. The front is expected to aid in the
development of some convection beginning Thursday and continuing into
Friday. Rain chances will be favored during the afternoon and early
evening hours as peak heating kicks in. Any remnants of the front
will likely dissipate Friday night as southerly winds return to all
areas.

For the upcoming weekend, there are some model differences regarding
the flow aloft. Regardless, it looks like the flow remains very weak
and disorganized. Temperatures should remain at or perhaps just
below normal along with a low chance for some afternoon showers and
storms across most of the region. If the GFS verifies in showing a
weak upper trough approaching from the west, we may need to boost
rain chances slightly. For now, we will keep rain chances capped at
20% for most of the region.

&&

.AVIATION...
(18Z TAFS)
Issued at 1226 PM CDT Mon Aug 15 2022

Highly variable conditions are evident at our terminals this
afternoon. Remnants of an upper disturbance continue to bring impacts
largely to DRT, SAT, and SSF, where cig reductions and RA/TSRA have
been reported periodically through the AM. Expect these trends to
continue to hold through the early afternoon at the Bexar County
terminals, and through the overnight at DRT. Have continued to hold
VCSH at SAT and SSF through 00Z to account for any remaining banded
precipitation in the vicinity. Have held at least VCSH mentions at
DRT through 15Z Tuesday, where rainfall will persist the longest of
the four aerodromes. Short term model guidance continues to point
toward a period of potentially heavier activity after midnight, so
have inserted a TEMPO +TSRA between 02 and 05Z to account for this
potential. Rain chances should finally reach their conclusion at DRT
by late tomorrow morning/early tomorrow afternoon.

Other big impact of the period will be cig reductions at all fields through
the overnight hours tonight. Have gone with prevailing MVFR at AUS,
SAT, and SSF from predawn through 15Z Tuesday, and have continued the
forecast for a period of IFR at DRT between 05 and 15Z Tuesday.
Conditions should gradually improve to VFR through the afternoon
hours tomorrow.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              98  76 101  77 /  10   0   0   0
Austin Bergstrom Intl Airport  97  74  99  75 /  10   0  10   0
New Braunfels Muni Airport     97  74  98  75 /  50   0  10   0
Burnet Muni Airport            96  74  98  74 /  10   0   0   0
Del Rio Intl Airport           82  75  91  76 /  90  70  40  10
Georgetown Muni Airport        98  75 100  76 /   0   0   0   0
Hondo Muni Airport             89  74  96  75 /  80  10  10   0
San Marcos Muni Airport        97  74  99  73 /  30   0  10   0
La Grange - Fayette Regional   97  75 100  76 /  10   0  10   0
San Antonio Intl Airport       92  75  96  76 /  70  10  10   0
Stinson Muni Airport           93  76  97  76 /  80  10  10   0

&&

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

Short-Term...Brady
Long-Term...Platt
Aviation...Quigley

Hazardous Weather Outlook
National Weather Service Austin/San Antonio TX
1054 AM CDT Mon Aug 15 2022

TXZ171>173-183>194-202>209-217>225-228-161600-
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-
1054 AM CDT Mon Aug 15 2022

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

.DAY ONE...This Afternoon And Tonight.

Areas of locally heavy rainfall is possible through tonight for
locations mainly along and to the west of the I-10 and I-37
corridor, especially in the Winter Garden region and along the Rio
Grande. The highest expected rainfall totals of 4 to 5 inches
over the Winter Garden region could result in minor flooding.
Later tonight into early Tuesday morning, isolated 2 to 4 inch
rainfall amounts may develop over parts of Val Verde county lead
to localized flooding.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not anticipated.

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