United States Record Setting Hail

July 23, 2010 - Vivan, SD

National Weather Service, Aberdeen, SD

July 23, 2020

During the late afternoon and evening of 23 July 2010, an intense supercell storm produced severe wind gusts, an EF0 tornado, and extremely large hail as it tracked southeastward across south-central South Dakota. The largest hailstone preserved from the storm was found in Vivian, SD and would go on to set United States records for maximum weight and diameter.

Setting the Stage

Surface analysis from 4 PM local time on 23 July 2010, depicted low pressure over south-central South Dakota, with a warm front (red) extending to the east-northeast and a cold front (blue) to the west-southwest.

Setting the Stage

Surface temperatures (red lines) had climbed to the upper 80s°F, while surface dew points (shading/blue dashed lines) reached the lower 70s°F. Surface mean sea level pressure is denoted in black.

Atmosphere - 6 PM Local Time

The atmosphere was highly unstable. Atmospheric instability (ML CAPE) was on the order of 4500 j/kg and in particular where hail forms (at an altitude where temperatures range between -10 C and -30 C) this value was around 1200 j/kg.

Atmosphere - 6 PM Local Time

In addition to the instability, high 0-6 km bulk shear values (changes in direction and speed of winds through the atmosphere) around 60 kts would enable storm rotation.

Atmosphere - 6 PM Local Time

The Supercell Composite Parameter (SCP) is a multiple component index that is meant to highlight the co-existence of ingredients favoring supercell thunderstorms. Any value over 1 is favorable for right moving supercells. SCP over south central South Dakota soared to 28.

Atmosphere - 6 PM Local Time

The Sig. Hail Parameter (SHIP) is based on 5 parameters, and is meant to delineate between SIG (>=2" diameter) and NON-SIG (<2" diameter) hail environments. SHIP values were around 2 on July 23, 2010.

Radar Loop

0.5 Degree Reflectivity

The storm that would eventually go on to produce record hail in Vivian initially started in southeast Haakon County, and by the time it moved into Jones County, it had already developed characteristics typical of a strong supercell. Large hail was already being reported when the storm did two more interesting things: it interacted with another supercell to the north, and ingested a pair of weaker storms that were moving northeast. The storm crossed into Lyman county, over the town of Vivian, at which point record hail began to fall out of the storm. The storm would continue to produce large hail as it moved east southeast along Interstate 90, finally weakening as it crossed the Missouri River.

Detailed Radar

Reflectivity

2258 UTC (left to right, top to bottom: 0.5, 0.9, 1.3, 1.8 degrees)

The storm was exceptionally tall, with a reflectivity core of 50-60 dBZ at nearly 45,000 ft.

The storm contained a Bounded Weak Echo Region (BWER) which is a local minimum in radar reflectivity at low levels which extends upward into, and is surrounded by, higher reflectivities aloft. This feature is associated with a strong updraft (rising air) which is needed for large hail to form.

A three body scatter spike (TBSS) was also observed. This is a spike of weak reflectivity echoes that extend out from a thunderstorm, and away from the radar site and is indicative of large hail.

Detailed Radar

Velocity

2258 UTC (left to right, top to bottom: 0.5, 0.9, 1.3, 1.8 degrees)

Strong middle level rotation was evident and is indicative of a strongly rotating updraft.

The maximum rotational velocities (1/2 * (|inbound velocity| + |outbound velocity|) were 71 kts at this time. At the peak, gate-to-gate velocity differences exceeded 110 kts.

Estimates indicate that the updraft strength in the Vivian hail storm was over 100 mph!

Local Storm Reports

First reports of hail were relayed at approximately 530pm CDT by an observer in Hayes, SD followed by several reports of golf ball sized hail as the storm neared Murdo. Additionally, wind gusts of 85 mph were observed as the storm moved over a weather station in the town of Draper. The largest hail (record setting), a brief tornado touchdown and destructive 80 mph winds were reported in and around Vivian, SD. The storm continued to produce large hail up to three inches in diameter as it moved on from Vivian and down along Interstate 90.

01 / 08

The Record

Several Vivian residents collected hailstones, including resident Les Scott, who gathered 10 hailstones of softball size or larger. One of those hailstones was preliminary estimated to have a diameter of 11 inches. Les considered mixing them into daiquiris. Thankfully he did not, and instead put them in the freezer.

The Record

National Weather Service Aberdeen staff traveled to Vivian, SD to confirm the legitimacy of the reported giant-sized hailstones and take measurements of the largest hailstone which would became known as "the Vivian Hailstone."

The Record

The Vivian Hailstone measured in 8.0 inches in diameter.

The Record

The Vivian Hailstone measured 18.625 inches in circumference.

The Record

The Vivian Hailstone weighed in at an astounding 1.9375 lbs.

The Record

On 28 July 2010, the National Climate Extremes Committee evaluated the validity of the stone and its measurements, and confirmed that the hailstone broke the US record for maximum diameter and weight. A Coffeyville, KS hailstone retained the record for circumference. Click the map locations for previous large hail records.

The Record

It is highly likely that melting and/or sublimation occurred due to exposure to the outdoors and precipitation before retrieval, repeated handling by the resident and onlookers, and the loss of power to the storage freezer before measurements were taken. Though the hailstone was certainly larger when it fell, the official dimensions were those recorded at the time of measurement.

The Record

In addition to this record hailstone, there were numerous other hailstones between baseball and softball size that went completely through vehicle windows, roofs, garages and campers. The hail caused five minor injuries to motorists on Interstate 90 as the hailstones broke through their windshields.

Research

The hailstone was packed in dry ice and relayed by meteorologists from Vivian, SD to Valentine, NE, from Valentine, NE to Cheyenne, WY and from Cheyenne, WY to Boulder, CO where National Center for Atmospheric Research (NCAR) scientist Charles Knight, studied and made casts of the original stone.

Aberdeen National Weather Service Meteorologist In Charge, James Scarlett, and hailstone discoverer, Les Scott, packing the hailstone for travel.

Research

“I think the bumps form very much the same way that icicles form. The hailstone is collecting more water than it can freeze, and that water flows over the outside of the stone and sheds off the top side as it falls. But it’s quite complicated.” - Charles Knight

Charles Knight prepares to make a three-dimensional model of the Vivian hailstone. (©UCAR. Photo by Carlye Calvin.)

10 Years Later

There are no winners when large, record breaking hailstones are found. However, 10 years later, no other hailstone has broken the diameter and weight records of the one found in Vivian, SD on July 23, 2010.