Special Weather Statement, NWS Austin/San Antonio, TX

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
309 PM CDT Thu Sep 3 2020

.SHORT TERM (Tonight through Friday Night)...
An outflow boundary, from morning convection across Central Texas,
is evident on radar and visible satellite and is now south of a
Giddings to Austin Bergstrom, to near Fredericksburg line.
Differential heating and this boundary have continue to lead to the
development of scattered showers and storms. Influence from a MCV
near Waco has also led to the continued development of showers and
storms north of the outflow boundary, across Williamson county. In
addition, elevated showers and storms are occurring across the
southeast CWA in the southwest flow aloft.

Convective initiation has also begun back into the Hill Country and
Edwards Plateau, roughly where many high-res models insisted, with
the help of diurnal heating, broad low level convergence, and mid
level PVA dropping south. Coverage of showers and storms should
continue to increase over portions of the northern I-35 corridor and
Hill Country over the next hour or so, and gradually build south and
southwest late afternoon and evening towards San Antonio and along
and south of U.S. 90 into a pool of MLCAPE values of 1000-2500 J/kg.
Strong storms, and an isolated severe storm or two, are possible,
with damaging wind gusts the primary threat given DCAPE values of
around 1400 J/kg. In addition, some pockets of locally heavy
rainfall are possible, and few locations could pick up a quick 1-3
inches leading to minor flooding.

There may be a downward trend in activity after sunset. However
several models indicate re-development of isolated to scattered
showers during the early morning hours. Therefore we will keep PoPs
in the forecast through the night. On Friday, the blends continue to
show high PoPs. With the mid and upper level trough axis over the
region we expect at least scattered convection though the day,
assisted also by daytime heating and mesoscale boundaries. Again,
some isolated pockets of heavy rainfall are possible. Highs tomorrow
should be cooler in many areas.

&&

.LONG TERM (Saturday through Thursday)...
An inverted, mid-level trough over the southern and eastern portions
of the state of Texas will slowly weaken on Saturday. The models
continue to show we will see plenty of atmospheric moisture in place,
with precipitable water values in the 1.5-2.25" range across south
central Texas. With afternoon heating and any remnant outflow
boundaries, we should see scattered showers and thunderstorms across
the region, especially during the afternoon hours. Given the amount
of moisture and weak flow aloft (slow storm movement), some locally
heavy rainfall is possible. We should see partly to mostly cloudy
skies as well and this along with expected rainfall should help keep
high temperatures in the upper 80s to mid 90s. For Sunday, the mid-
level trough continues to weaken, while the atmosphere begins to
slowly dry out. We should see a downward trend in rain chances, but
we will keep a mention of showers and storms for areas generally
south of a Del Rio to Austin line. Temperatures should warm slightly
given a decrease in expected cloud cover. However, we should still
see highs right at climatological normals for early September.

Most areas will remain precipitation free on Monday as the mid-levels
continue to dry and stabilize. The exception will be near the coastal
plains where the afternoon sea breeze will likely help initiate some
afternoon showers and storms. It will be warm and humid on Monday
with highs back into the 90s for most areas. The weather pattern
will begin to change on Tuesday as the medium range models show
either a closed low or very sharp upper trough dropping southward
through the southern Rockies. We could see a slight uptick in the
southwest flow aloft and this along with daytime heating should allow
for some afternoon convection to develop. With moisture levels
higher to our east, rain chances will be favored generally east of
I-35. High temperatures on Tuesday will be in the 90s and if the
low-level thermal ridge continues to amplify, we may need to boost
highs on Tuesday in later forecasts.

A significant change in the weather pattern is advertised mid-late
week as the first stout cold front in what seems like a long, long
time moves southward into the southern U.S. plains. There are
differing model solutions with how fast the cold front moves into the
region. The GFS and Canadian are faster, while the ECMWF is slower.
The consensus seems to be trending with the faster moving cold front
and we will follow this solution for now. This scenario will bring
the cold front into the region late Tuesday or early Wednesday. Much
cooler temperatures are in store for Wednesday and Thursday, with
highs in the upper 70s to mid 80s. Overnight lows will also trend
downward and if we can manage to get some breaks in the overnight
cloud cover, lows in the mid-50s are possible across the Hill Country
Wednesday night. With a mid-level trough axis moving in from the
west, we should see some scattered showers and thunderstorms across
the region on Wednesday and Thursday.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              73  87  73  91  73 /  40  60  20  40  -
Austin Bergstrom Intl Airport  73  86  72  91  72 /  40  60  20  40  -
New Braunfels Muni Airport     73  87  72  92  72 /  60  60  20  40  -
Burnet Muni Airport            71  84  71  88  69 /  40  60  20  30   0
Del Rio Intl Airport           75  92  75  93  74 /  50  60  50  40  20
Georgetown Muni Airport        73  86  72  91  72 /  40  60  20  40   0
Hondo Muni Airport             74  90  72  94  72 /  60  60  30  40  10
San Marcos Muni Airport        73  87  72  91  72 /  50  60  20  40  -
La Grange - Fayette Regional   76  91  74  94  74 /  40  60  20  40  -
San Antonio Intl Airport       75  89  74  93  74 /  60  60  20  40  -
Stinson Muni Airport           75  89  74  92  75 /  60  60  20  40  10

&&

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

Short-Term/Aviation...Runyen
Long-Term...Platt
Decision Support...05

Hazardous Weather Outlook
National Weather Service Austin/San Antonio TX
345 AM CDT Thu Sep 3 2020

TXZ171>173-183>194-202>209-217>225-228-041200-
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-
345 AM CDT Thu Sep 3 2020

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

.DAY ONE...Today And Tonight.

Scattered to numerous showers and thunderstorms are expected today
and this evening across much of the area. The strongest storms
will bring locally heavy rainfall and gusty winds.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

Additional rainfall is likely across the region Friday through
Sunday and at times could pose a heavy rainfall threat. The
location and timing of the heaviest rain is still uncertain, so
continue to check forecasts and outlooks for updated information.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not anticipated.

Special Weather Statement
National Weather Service Austin/San Antonio TX
127 PM CDT Thu Sep 3 2020

TXZ192-031915-
Travis TX-
127 PM CDT Thu Sep 3 2020

...SIGNIFICANT WEATHER ADVISORY FOR CENTRAL TRAVIS COUNTY UNTIL 215
PM CDT...

At 126 PM CDT, Doppler radar was tracking a strong thunderstorm over
West Lake Hills, or near Austin, moving northeast at 5 mph.

Wind gusts up to 50 mph will be possible with this storm.

Locations impacted include...
Austin, Bee Cave, West Lake Hills, Hudson Bend, Rollingwood, Barton
Creek, Mansfield Dam, Sunset Valley, Camp Mabry, and Lost Creek.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Torrential rainfall is also occurring with this storm, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

&&

LAT...LON 3018 9780 3030 9795 3047 9787 3029 9761
TIME...MOT...LOC 1826Z 223DEG 5KT 3030 9782

BF

Special Weather Statement
National Weather Service Austin/San Antonio TX
316 PM CDT Thu Sep 3 2020

TXZ184>187-032115-
Kerr TX-Edwards TX-Real TX-Bandera TX-
316 PM CDT Thu Sep 3 2020

...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN BANDERA...
NORTHWESTERN KERR...EASTERN EDWARDS AND REAL COUNTIES UNTIL 415 PM
CDT...

At 316 PM CDT, Doppler radar was tracking a strong thunderstorm 13
miles south of Telegraph, or 19 miles northeast of Rocksprings,
moving south at 10 mph.

Nickel size hail and wind gusts up to 50 mph will be possible with
this storm.

Locations impacted include...
Leakey, Vanderpool, Hunt, Barksdale, Tuff, Vance, Kerr Wildlife
Management Area, Mountain Home, Lost Maples State Natural Area, I-
10 Near The Kimble-Kerr County Line, Us-377 Near The Kimble-
Edwards County Line, Us-83 Near The Kerr-
Kimble County Line, The Intersection Of I-
10 And Us 290 and Prade Ranch.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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 3029 9931 2991 9933 2969 9958 2969 10006
      3029 10005
TIME...MOT...LOC 2016Z 344DEG 10KT 3013 9991

AAT