An upper level trough moved over a warm, moist airmass and generated thunderstorms. Some of these storms produced locally heavy rain that led to flash flooding.
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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.
An upper level trough moved over a warm, moist airmass and generated thunderstorms. Some of these storms produced locally 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 Aug 18, 9:37 AM CST, 1 hour 23 minutes earlier.
Area Forecast Discussion...UPDATED National Weather Service Austin/San Antonio TX 1037 AM CDT Wed Aug 18 2021 .UPDATE... Updated and increased PoPs across the southern Edwards Plateau and western Hill Country through mid afternoon. Convection is expected to keep ongoing through the next several hours over these locations with the passage of a mid level short wave through the area. Precipitable water values range from 2.2 to 2.3 inches, which bring the potential for heavy rain and flash flooding. Then later this afternoon, the activity is forecast to shift to the northern Hill Country and areas mainly along and east of Highway 183. As far as temperatures go, dropped them a few degrees across the Edwards Plateau, Hill Country and eastern zones based on current observations and short term forecast trend. Anyway, they still be able to reach the upper 80s to lower 90s with upper 90s across the southwest part of South Central Texas. Still advertising heat index values around 105 to 108 degrees across the southern counties. Can't rule out readings up to 110 degrees during peak heating or around the 3 to 4 pm time frame. && .PREV DISCUSSION... /ISSUED 623 AM CDT Wed Aug 18 2021/ AVIATION... Seeing some showers beginning to develop on radar this morning near KSAT northward to just west of KAUS. In addition, there are a few showers north of DRT as well. Will begin the TAFs off with VCSH to cover this threat. MVFR ceilings are prevailing for the I35 sites and should lift by the mid-morning hours. Could see some additional showers or storms through the day with showers possibly continuing into the evening hours mainly closer to DRT. PREV DISCUSSION... /ISSUED 219 AM CDT Wed Aug 18 2021/ SHORT TERM (Today through Thursday)... Latest water vapor imagery shows that the center of the shortwave trough is currently near the Texas/Oklahoma border at this time. To the south of this feature, weak troughing can be noted and this is leading to localized areas of rainfall production overnight. The heaviest activity, which is rooted in the boundary layer remains just to the north of our CWA, while some weak elevated returns can be seen across our western counties. Different high-res models have different solutions for today, but we can mostly discount the 00z NAM and ARW for this forecast package as both of these models progged decent QPF by now in the Hill Country and Edwards Plateau. On the flip side, the HRRR, FV3, and TTU WRF all have seemed to initialize much better. Following these solutions, points to possible development of additional activity along and east of the I35 corridor around daybreak moving north/northeastward this morning. However, the bulk of the precip looks to remain to our north in closer proximity to the departing shortwave trough. Therefore, have went with slightly lower PoPs than the NBM in the short-term to better align with the suite of models which seemed to have initialize better. As a consequence, went a degree or two degrees warmer on highs today to account for the lesser coverage of rainfall activity. Additionally, dewpoints this afternoon across the southern third of the area will remain in the upper 70s which should lead to heat index values near 105-108 degrees. This should be mostly below Heat Advisory Criteria and will handle this with an SPS instead. For tonight, the best area for possible rainfall will likely be in the southwest CWA as there are indications in both the global and the high-res models that an embedded disturbance could lead to rainfall there. Otherwise, another muggy night is in store for South- Central Texas. The main risk with any activity today and tonight will be the threat for locally heavy rainfall. PWs at or above 2 inches for much of the area which will aid in efficient rainfall production. WPC has all but the Coastal Plains in a marginal risk for excessive rainfall for today and tonight. Things should finally start to dry out some on Thursday as 500 mb heights are progged to begin to increase as upper ridging begins to strengthen across the region. Will hold onto slight chance PoPs for the eastern and northern CWA. With the increasing heights, highs should be 2-3 warmer than today, topping out in the lower to upper 90s. LONG TERM (Thursday Night through Tuesday)... Short version: A much drier outlook is in store Thursday night through early next week with only a few low chances for precipitation mainly east of I-35. The best chances will be on Friday and Saturday afternoons. With subtropical ridging strengthening across the southern CONUS Sunday and beyond, we'll undergo a warming trend and daytime highs are likely to be much to seasonal norms into the middle of next week. Longer version: As the long term begins Thursday evening, diminishing shower and storm activity may still impact western Val Verde County in association with a shortwave located near the Big Bend region, but at this time precip chances are higher to the west of our area. During the day, some isolated seabreeze development is forecast for the Coastal Plains, with a very low chance for some rain to reach the I-35 corridor. Saturday afternoon rain chances will be just a tad higher in modest onshore flow as Grace makes landfall far, far to our south, somewhere along the Mexico coast in Veracruz. Not anticipating much in the way of coverage and many locations are likely to remain dry, but slight chance POPs will extend west of I-35 to a line approximately from Eagle Pass to Georgetown. Sunday and beyond, ridging will gradually build with consensus in 594-595 dm H5 heights centered somewhere over TX by Monday night. Winds will be primarily out of the SE at the surface as is typical this time of year, with occasionally breezy conditions across the Rio Grande Plains and southern Edwards Plateau. Moisture will remain elevated, but ample daytime sunshine and subsidence should allow for daytime highs to climb back into the mid and upper 90s especially by Tuesday and Wednesday. Elevated heat indices, highest southeast, could briefly approach Heat Advisory thresholds. Will see very low PM precip chances (<25%) across mainly Lavaca, Dewitt, and Fayette counties each afternoon. PREV DISCUSSION... /ISSUED 1201 AM CDT Wed Aug 18 2021/ AVIATION... Scattered showers continue just north of AUS and patchy light rain continues near DRT but no significant impacts are expected through the overnight hours. Should see some MVFR ceilings at the terminals by morning and these should lift by the mid-morning hours. Convective evolution will be messy again today, but think we should see some scattered activity continue this afternoon and perhaps a larger complex of rain out near DRT tonight and will show that in the TAFs. Amendments and/or changes in future TAF issuances will likely be needed as the forecast changes. && .PRELIMINARY POINT TEMPS/POPS... Austin Camp Mabry 89 78 96 77 94 / 50 20 10 - 20 Austin Bergstrom Intl Airport 89 78 95 76 94 / 50 20 10 - 20 New Braunfels Muni Airport 91 77 97 77 95 / 40 20 - - 20 Burnet Muni Airport 87 76 92 76 93 / 50 30 10 - 10 Del Rio Intl Airport 94 79 97 77 98 / 20 30 10 - - Georgetown Muni Airport 88 77 94 76 94 / 50 30 20 - 10 Hondo Muni Airport 96 77 97 76 95 / 20 30 - 0 10 San Marcos Muni Airport 90 77 95 76 95 / 50 20 10 0 20 La Grange - Fayette Regional 91 79 96 79 96 / 50 20 20 0 20 San Antonio Intl Airport 94 78 96 77 94 / 30 20 - - 20 Stinson Muni Airport 96 79 99 79 97 / 20 20 - - 20 && .EWX WATCHES/WARNINGS/ADVISORIES... None. && Short-Term/Aviation...17 Long-Term...Morris Decision Support...Runyen
Hazardous Weather Outlook National Weather Service Austin/San Antonio TX 325 AM CDT Wed Aug 18 2021 TXZ171>173-183>194-202>209-217>225-228-191200- 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- 325 AM CDT Wed Aug 18 2021 This Hazardous Weather Outlook is for South-Central Texas.. .DAY ONE...Today And Tonight. Through tonight, showers and thunderstorms may produce locally heavy rain for locations along and north of an Eagle Pass to San Antonio to Austin line. Isolated rainfall amounts in excess of 3 inches are possible, with the highest risk along our northern border. Afternoon heat index values will be up to 105-108 degrees for areas along and south of an Eagle Pass to Pleasanton to La Grange line. .DAYS TWO THROUGH SEVEN...Thursday through Tuesday. No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation is not anticipated.
The Laughlin AFB radar (KDFX), 62 km away, was scanning. The volume nearest the first event began at 16:58 UTC.
1 flash flood, 1 lightning. Local standard time, as filed.
Thunderstorms produced heavy rain that led to flash flooding. FM 335 was flooded near the Nueces River north of Barksdale.
Lightning struck an oil tank battery southwest of Hallettsville. The lightning strike caused an explosion and fire. Of the eight tanks on site, three were destroyed and five severely damaged.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Texas in 2021Every state in 2021This day in weather historyWarnings in Texas, August 2021
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: 979853, 979854.