The September 24, 2023 Round Rock / North Austin Hail Storm
Revisiting the Giant Hailstorm
Introduction
On the evening of September 24, 2023 a severe supercell produced giant sized and destructive hail along the Interstate 35 corridor between Georgetown and the north side of Austin, Texas. The city of Round Rock experienced the largest hail, up to 4 inches in diameter (softball sized). The destructive hail fell over an urban area, producing damage to roofs, vehicles, and windows. This one storm produced over $600 million (2023 USD) in estimated damages. When combined with other severe storms in the Central Texas region September 23-24, over $1 billion (2023 USD) in estimated damages were reported, making it one of 28 billion-dollar weather and climate disasters in the United States in 2023. This StoryMap looks back at the hail track, radar imagery, atmospheric setup, timeline, and pictures from this hail storm.
Billion Dollar-Weather and Climate Disasters from 2023 - The Central Texas hail storms on September 23-24, including the Round Rock storm, are one of 28 billion-dollar disasters from 2023. The Round Rock storm produced $600 million in damages alone.
Giant hail stones collected in the North Austin/Round Rock area
The severe supercell that produced the giant hail was highly electrified with continuous lightning observed. (Video Courtesy Levi Riggins)
Hail Map
Radar Loop
Base Reflectivity loop from the Granger (GRK) radar showing the supercell that produced the giant hail moving down the Interstate 35 corridor from Georgetown, through Round Rock, and into the north side of Austin.
Three dimensional view of Reflectivity from Granger (GRK) radar over Round Rock, TX. The white and purple shades are large hail suspended aloft and falling through the downdraft to the surface. The top of this storm was between 50 and 60 thousand feet above the ground.
Technical Discussion
Upper level high pressure was situated across northern Mexico leading up to the event with a weak upper level trough passing through Oklahoma into North Texas. This system would interact with a slow moving cold front to the north of the area to allow for storm development during the evening hours. The convective environment was very conducive for any storm to quickly intensify as afternoon temperatures ranging from the middle to upper 90s led to surface-based CAPE values in excess of 3000 J/kg. Dewpoints were near 70 degrees, which helped ensure that there was little to no inhibition to prevent storm development. With the upper ridge to the southwest and the approaching upper trough to the north, mid-level flow was strong enough to lead to effective shear values near 30-35 knots. Given this CAPE and shear environment, any storm that developed had the potential to quickly become severe with the capability of producing very large hail.
Storms initially developed just after 7 PM in the Hill Country over Blanco and Gillespie County in an area of modest low-level convergence ahead of the approaching weak frontal boundary with upper support from the approaching upper trough. These storms did become severe, producing 1 inch diameter (quarter sized) hail. Shortly after this development, the storm that would eventually affect Round Rock developed in northwest Williamson County around 7:40 pm and then tracked to the south-southeast slowly near 10 mph. With the atmosphere highly unstable, this storm continued to strengthen as it progressed south-southeast and produced hail in excess of 2 inches in diameter in Georgetown around 8:45 pm. The storm then continued to move south-southeast where it intensified and produced its largest hail size through the life-cycle of the storm with 3 to 4 inch diameter hail stones reported across the city of Round Rock mainly between 9:15 and 9:25 pm. After the storm peaked it produced severe hail ranging from 1.5 to 2.25 inches in the city of Austin along and just west of Interstate 35 before the storm finally weakened as it approached the Colorado River south of downtown Austin around 10:30 pm.
Event Timeline
Graphic for the Mesoscale Discussion issued from the Storm Prediction Center illustrating the potential for severe thunderstorms from the Hill Country north toward the DFW Metroplex.
Graphic showing the Texas counties included in Severe Thunderstorm Watch from the Storm Prediction Center.
Image showing the severe thunderstorm warning polygon issued by NWS Austin/San Antonio for portions of Burnet and Williamson Counties at 6:55 PM CDT.
Image showing the severe thunderstorm warning polygon issued by NWS Austin/San Antonio for portions of Williamson County at 7:55 PM CDT.
Image showing the severe thunderstorm warning polygon issued by NWS Austin/San Antonio for much of the Austin metro and points southeast at 9:40 PM CDT.
