The airmass over South Central Texas was very moist with high precipitable water. A weakness developed in the ridge in the mid-levels of the atmosphere above this moist boundary layer.
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Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS EWX wrote it up.
The airmass over South Central Texas was very moist with high precipitable water. A weakness developed in the ridge in the mid-levels of the atmosphere above this moist boundary layer. This allowed thunderstorms to develop and some of these storms produced heavy rain that led to flash flooding.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Austin/San Antonio, TX wrote its last area forecast discussion before the first event at Sep 4, 5:33 AM CST, 2 hours 27 minutes earlier.
Area Forecast Discussion National Weather Service Austin/San Antonio TX 633 AM CDT Fri Sep 4 2020 .AVIATION... SHRA will move across KAUS this morning with TS in the VCNTY with VCSH at the other sites. SHRA/TSRA will be more numerous by this afternoon and continue into at least this evening and have gone VCTS with the expectation that one or more sites will need updating to prevailing SHRA/TSRA. The SHRA/TSRA should wane late evening into the overnight hours. MVFR CIGs will lift to VFR late this morning. MVFR CIGs are possible again overnight at KSAT/KSSF. Variable mainly easterly winds less than 10 KTs will prevail. However wind gusts up to 40 KTs are possible with the stronger TSRA Friday. && .PREV DISCUSSION... /ISSUED 335 AM CDT Fri Sep 4 2020/ SHORT TERM (Today through Saturday)... An upper level trough remains over South Central Texas early this morning. Two MCVs formed from yesterday's afternoon into evening showers and thunderstorms, one south of San Antonio and the other northeast of Austin. Showers and thunderstorms will gradually increase this morning due to a moist airmass and weak upward forcing from the trough and MCVs. Models have various locations of the redevelopment and none capture the locations of the ongoing redevelopment. With that in mind, as well as, additional surface boundaries to provide upward forcing will use the blended POPs for today into this evening with scattered to numerous showers and thunderstorms. PWs near 2 inches and slow or repeat storm motions indicate a potential for locally heavy rains and possible minor flooding. Moderate DCAPE suggests a potential for strong winds gusts with the strongest storms. Expect showers and thunderstorms to wane tonight with loss of heating while the upper level trough gradually weakens and drifts to the southwest. Isolated to scattered showers will redevelop on Saturday due to heating and weak upward forcing from the trough of a moist airmass. Locally heavy rains and gusty winds, although possible, will be more isolated. Below normal high temperatures are expected due to the clouds and rain. LONG TERM (Saturday Night through Thursday)... With the upper trough weakening, Sunday should continue the drying trend with lower chances for showers and storms. Temperatures are also on the upward trend with less rain and less clouds in the area. Highs though should remain near normal for Sunday and Monday. Monday will be mostly dry with only some stray showers from the coast. All eyes are on the potentially strong cold front progged for Tuesday/Wednesday. While both the GFS and Euro show a deep trough dig into the central US before cutting off a low over the Rockies. The GFS offers a more progressive run with the low and associated cold front with a much cooler airmass down into south central Texas. The Euro is still showing the low hanging out over the Rockies through Thursday before it lifts to the northeast, keeping the colder air north of the area. What the models do agree on are the increased rain chances for mid-week next week. Chance PoP starts on Tuesday afternoon, then becoming likely throughout the day Wednesday for most of the area. && .PRELIMINARY POINT TEMPS/POPS... Austin Camp Mabry 85 73 89 73 91 / 80 30 50 10 20 Austin Bergstrom Intl Airport 85 71 88 71 90 / 70 30 50 10 20 New Braunfels Muni Airport 86 72 88 72 91 / 80 30 50 20 30 Burnet Muni Airport 83 71 86 69 89 / 80 30 50 10 20 Del Rio Intl Airport 93 74 91 74 92 / 60 20 60 40 10 Georgetown Muni Airport 85 72 88 71 91 / 80 30 50 10 20 Hondo Muni Airport 89 73 91 72 92 / 70 30 50 20 30 San Marcos Muni Airport 86 71 88 71 91 / 80 30 50 10 30 La Grange - Fayette Regional 90 74 92 74 94 / 70 30 50 10 20 San Antonio Intl Airport 88 74 90 74 92 / 80 30 50 20 30 Stinson Muni Airport 88 74 90 74 91 / 70 30 50 20 30 && .EWX WATCHES/WARNINGS/ADVISORIES... None. && Short-Term/Aviation...04 Long-Term...YB
Hazardous Weather Outlook National Weather Service Austin/San Antonio TX 414 AM CDT Fri Sep 4 2020 TXZ171>173-183>194-202>209-217>225-228-050915- 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- 414 AM CDT Fri Sep 4 2020 This Hazardous Weather Outlook is for South-Central Texas.. .DAY ONE...Today And Tonight. Scattered to numerous showers and thunderstorms are expected today into this evening. Locally heavy rainfall and gusty winds are possible with the strongest storms. .DAYS TWO THROUGH SEVEN...Saturday through Thursday. Scattered showers and thunderstorms are expected Saturday. Locally heavy rainfall and gusty winds are possible with the strongest storms. .SPOTTER INFORMATION STATEMENT... Spotter activation is not anticipated.
The Austin/San Antonio radar (KEWX), 47 km away, was scanning. The volume nearest the first event began at 14:01 UTC.
2 flash flood. Local standard time, as filed.
Thunderstorms produced heavy rain that led to flash flooding. ATXFloods reported that Onion Creek ran out of its banks closing Garrison Rd. in Buda.
Thunderstorms produced heavy rain that led to flash flooding along the Andrews Branch in Buda. ATXFloods reported that Dacy Ln. was flooded north of Windy Hill Rd.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Texas in 2020Every state in 2020This day in weather historyWarnings in Texas, September 2020
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 920676, 920677.