The May 9th, 2024 Large Hail and Damaging Wind Storms
A look back at the two prolific supercell thunderstorms that produced giant hail and strong damaging winds across the Hill Country and I-35
Introduction
A series of supercell thunderstorms moved through the Texas Hill Country and I-35 Corridor during the evening of May 9. One of these storms produced giant hail and damaging wind gusts from Johnson City to near Luling. The third largest hailstone ever reported in Texas fell in Johnson City. The most extensive wind damage was in San Marcos. This StoryMap documents the event showing the storm track, radar imagery, atmospheric setup, timeline, and pictures of the hail and wind damage.
Local storm reports, includes the reports of large hail and damaging winds, from the night of May 9th from the supercells that tracked through the Hill Country and the I-35 corridor.
Photo of the third largest hailstone in the Texas state records that fell on May 9th in Johnson City, Texas. The Insurance Institute for Business and Home Safety estimated the size of the stone at 6.14 inches in diameter at the time of this photo.
Paul Yura (pictured measuring the hail stone), our Warning Coordination Meteorologist, and Jon Zeitler, our Science Operations Officer, traveled out to Johnson City about a week after the storm to measure the pictured third largest hailstone in state history. While the hailstone was promptly placed in the freezer after the storm, it still had shrunk down to 5.4 inches in diameter as a result of sublimation.
A loop of the GOES-16 sandwich composite satellite imagery throughout the duration of the severe thunderstorm event from the night of May 9th across Texas where the infrared satellite imagery is overlayed on top of the daytime visible satellite imagery.
Hail Map
Image of the hail swaths in association with the supercells that moved through the Hill Country and across the I-35 corridor from the night of May 9th; this includes estimated hail sizes with each of the hail swaths from the Multi-Radar Multi-Sensor (MRMS) system.
Radar Loop
Base Reflectivity loop from the New Braunfels (EWX) radar showing the supercells that produced the giant hail and damaging winds moving southeastward from the Hill Country across the I-35 corridor, including impacts to Johnson City and San Marcos, Texas.
Three dimensional view of Reflectivity from New Braunfels radar over Johnson City, TX. The white and purple shades are very large hail suspended aloft and falling through the downdraft to the surface. The top of this storm was between 50,000 and 60,000 feet above the ground.
Technical Discussion
A large, positively tilted upper-level trough covered much of the continental United States. An embedded mid to upper-level low moved slowly toward the eastern Great Basin, with moderate to strong westerly midlevel flow extending eastward across the Southern Plains. A cold front moved across parts of the Southern Plains during the day.
The morning surface analysis showed the front quasi-stationary through a weak low south of Abilene with a dryline extending south into the Big Bend region. This front sagged southward through the day, and stalled across the Edwards Plateau. In the warm sector south of the front and east of the dryline dewpoint temperatures were in the middle to upper 70s making the airmass strongly buoyant. Mesoanalysis showed 3000-4000 J/kg of surface-based CAPE, 50-60 kts of effective bulk wind shear, and 700-500 mb lapse rates near 8.0 °C/km. In their noon update, the Storm Prediction Center extended the Enhanced (Level 3 of 5) Risk into the eastern Hill Country and northern I-35 Corridor with the Slight (Level 2 of 5) Risk surrounding it.
Storms initially formed near the intersection of the dryline and the front near San Angelo around 3 pm. There were several reports of half dollar size hail as this storm moved toward the southeast. This storm developed into the first supercell producing tennis ball size hail in Brady. A second updraft developed as the storm entered northern Blanco County around 7 pm. This became the supercell that produced the giant hail and most damaging winds. This storm intensified rapidly as it moved toward the southeast producing hail up to 6.14 inches at 7:21 pm in Johnson City. It continued to drop tennis ball size hail as it moved through western and central Hays County. When the storm got near San Marcos strong wind gusts accompanied the hail. The strongest wind gusts were estimated at 80 mph and caused damage in San Marcos, Martindale, and Staples. The storm weakened as it crossed I-10 and turned toward the east around 9:30 pm.
Event Timeline
2:48 PM CDT May 09, 2024
The Storm Prediction Center (SPC) releases updated Day 1 Convective Outlook highlighting a level 3 (enhanced) risk for severe thunderstorms across the Hill Country into the I-35 corridor. A level 2 (slight) risk to level 1 (marginal risk) was also issued farther southwest and south of the level 3 risk. Greatest concerns was for very large hail followed by damaging winds and the potential for a few tornadoes.
5:45 PM CDT May 09, 2024
The Storm Prediction Center (SPC) in coordination with the Weather Forecast offices issues a Severe Thunderstorm Watch until 12:00 AM CDT for portions of the Hill Country and the Interstate 35 corridor from Hays, Caldwell counties northward. Scattered large hail with isolated very large hail up to 3 inches in diameter (apple size), scattered damaging wind gusts including isolated significant gusts up to 80 mph were possible. A couple of tornadoes were possible but was a lower threat in comparison to the large hail and damaging winds.
5:51 PM CDT May 09, 2024
A supercell thunderstorm was approaching our Hill Country counties and prompted a tornado warning across Llano County. This thunderstorm was already tornado warned by the NWS San Angelo office across Mason and San Saba counties as the radar indicated enough rotation for a possible tornado. A tornado did not occur across the area. The NWS Austin/San Antonio tornado warning included the potential for large hail as well of up to 2 inches in diameter.
6:29 PM CDT May 09, 2024
The supercell thunderstorm had now entered Llano county and was no longer indicating rotation for a possible tornado. As a result, a Severe Thunderstorm warning instead of a tornado warning had been issued across Llano county. The thunderstorm was warned for consisting of large hail and strong damaging winds.
6:58 PM CDT May 09, 2024
A new Severe Thunderstorm Warning was issued downstream across portions of Blanco, Burnet, Llano and Gillespie Counties. This had included the town of Johnson City located in Blanco County.
7:20 PM - 7:30 PM CDT May 09, 2024
Numerous storm reports of large to very large hail near or within the town of Johnson City in Blanco County. This includes the 6.14 inch estimated hailstone.
7:34 PM CDT May 09, 2024
After receiving the very large storm reports from Johnson City, a Destructive Severe Thunderstorm Warning was issued from Blanco into Hays and Travis counties with the potential for baseball plus size hail.
8:00 PM CDT May 09, 2024
A Severe Thunderstorm Warning was issued across Burnet into Williamson Counties as a second supercell capable of large hail and strong damaging winds entered the region.
8:22 PM CDT May 09, 2024
Tornado Warning issued across Hays into Caldwell and Guadalupe Counties as the supercell across Hays County nearing San Marcos as radar indicated a strengthening circulation within the storm. This circulation to the northwest of San Marcos was brief and then got overtaken by a region of very strong straight line winds in excess of 70 mph. A tornado did not occur as a result of the brief circulation. The much greater impacts from this storm was the very large hail and those very strong winds.
8:25 PM - 8:35 PM CDT May 09, 2024
Several reports of very large hail up to tennis ball size and strong damaging winds knocking down trees, power lines, and leading to minor structural damage reported in San Marcos and southeastern portions of Hays County. A damage survey conducted the day after the storm estimated that the wind damage was caused by an estimated wind speeds between 65 and 75 mph.
8:29 PM CDT May 09, 2024
A new Severe Thunderstorm Warning was issued as the northern most supercell entered Williamson county. This warning indicated the potential for large hail of 2 inches in diameter or greater and winds above 60 mph.
8:36 PM CDT May 09, 2024
As the damage reports still were coming in from the supercell near San Marcos and across Southeastern Hays County, a new Severe Thunderstorm Warning was extended for this cell through Caldwell, Guadalupe counties and into Gonzalez County. Damaging straight line winds in excess of 70 mph and hail up to tennis ball size remained the primary hazards.
8:40 PM - 9:00 PM CDT May 09, 2024
Additional damaging wind reports arrive across Caldwell and Guadalupe counties from the southern severe storm, including within the towns of Martindale and Staples. The outflow advancing away from the storm had also produced several wind gusts of 59 and 61 mph.
9:11 PM CDT May 09, 2024
New Severe Thunderstorm Warning was issued into portions of Dewitt, Karnes, Gonzalez, Lavaca and Wilson Counties for the southern supercell that was located over Caldwell and Guadalupe counties. Winds around or in excess of 60 mph and up to 2 inch in diameter hail were the main threats. The warning had been larger than usual and flared out to capture the severe winds along the outflow boundary that pushed out of the storm.
9:20 PM CDT May 09, 2024
New Severe Thunderstorm Warning was issued into portions of Bastrop, Lee and Travis counties on the northern supercell that was located across southeastern Williamson county. Like the previous warning, winds around or in excess of 60 mph and up to 2 inch in diameter hail were the main threats. Additionally, like the southern storm, the warning also had been larger than usual and flared out to capture the severe winds along the outflow boundary that pushed out of the storm.
10:04 PM CDT May 09, 2024
The final Severe Thunderstorm Warning of the night was issued for the northern supercell across portions of Lee and Fayette Counties. The main threats continued to be winds in excess of 60 mph and hail up to 2 inches in diameter.
10:08 PM CDT May 09, 2024
Final storm report of the night was 2 inch diameter hail that fell in the town of Giddings.
Pictures
Hail and wind damage photos from the Hill Country into the I-35 corridor and into portions of the coastal plains.
