Figure 1: The devastating, large hailswath produced by the long-lived HP supercell is shown in yellow (primary swath). Smaller hailswaths produced by 2 other supercells are shown in blue. The cumulative hailswath produced by all three supercells is 325 miles (525 km) in length. The longer tornado tracks are also evident as red lines.
Figure 2: Tracks of the supercells observed with each color representing a different storm. The track of the HP supercell that produced the historic hailstorm is in red. This HP evolved over western Missouri between 2200-2230 UTC from the merger of two supercells with classic structure. Longevity of the HP supercell was over 5 hours.
Figure 3: Manual surface analysis for 2200 UTC 10 April 2001 showing the stationary front which the storm became anchored to and tracked along.
Figure 4: Barograph trace from the NWS office in Weldon Spring (KLSX) showing first a pressure dip associated with the mesolow, followed by sharp rise associated with the wake bubble-high passage.
 
 
 
 
Figure 5: Destroyed mobile home near Route F around 1 mile west of Highway 54 in Fulton.
Figure 6: A collapsed storage garage along the South Outer Road of Interstate 70, east of the Foristell exit in western St. Charles County.
Figure 7: Damage to an apartment complex in Lake St. Louis.
Figure 8: Damage to an apartment complex in the Granite City-Pontoon Beach area.
Figure 9: Radar loop from the Springfield WSR-88D (KSGF) covering the period from 2026-2217 UTC. This loop shows one radar viewing angle of the merger and development of the HP supercell near KEAX.
Figure 10: Radar loop from the Kansas City/Pleasant Hill WSR-88D (KEAX) covering the period from 1921-2251 UTC. This alternative radar view shows at very close range the merger and development of the HP supercell.
Figure 11: A 4-panel view of the two supercells at 2141 UTC from the KEAX WSR-88D. Base reflectivity is on top and storm-relative velocity is on the bottom, while the right images are from the 16.7° radar elevation and the left images are from 0.5°. Intense rotating updrafts are evident with the appearance of Bounded Weak Echo Regions (BWERs) in the reflectivity data and mesocyclones (dashed) in the SR velocity data.
Figure 12: A 4-panel view of the merger of the two supercells at 2211 UTC from the KEAX WSR-88D. Base reflectivity is on top and storm-relative velocity is on the bottom, while the right images are from the 8.7° radar elevation and the left images are from 0.5°. A large updraft region is evident in the 8.7° reflectivity data with multiple intense updraft centers (note two BWERs).
Figure 13: A west-east oriented radar reflectivity cross section from the KLSX WSR-88D at 0058 UTC when the HP supercell was centered in Montgomery County Missouri. The cross section depicts a large updraft region with multiple intense centers, and an echo overhang of around 10 miles.
Figure 14: Radar loop from the St. Louis WSR-88D (KLSX) covering the period from 0129-0246 UTC, when the supercell was producing destructive hail across the St. Louis Metropolitan Area. This loop also shows the unusual transition from a HP storm structure to a more classical supercell structure as the storm exits Missouri and moves into Madison County Illinois.
Figure 15: A 4-panel view at 0129 UTC as the HP supercell was beginning to move into western St. Charles County. The velocity images on the bottom depict an intense rear flank downdraft (winds of 70+ mph) and mesocyclone which comprise a feature know as a “Deep Convergence Zone” or DCZ. The white line marks the leading edge of the storm’s gust front.
Figure 16: A 4-panel view at 0144 UTC of the HP supercell while it was producing a tornado near Interstate 70 between Foristell and Wentzville in St. Charles County. Reflectivity is on top and storm-relative velocity is on the bottom, while the right images are from the 8.7° radar elevation and the left images are from 0.5°. A mesocyclone and tornado cyclone are evident in the storm-relative velocity data. Note that the tornado is in the rear of the storm embedded in precipitation.
Figure 17: 0.5° KLSX radar reflectivity image at 0215 UTC when the storm was producing destructive hail in northern St. Louis County including Lambert-St. Louis International Airport.
Figure 18: A west-east oriented radar reflectivity cross section from the KLSX WSR-88D at 0215 UTC when the HP supercell was producing destructive hail in northern St. Louis County including Lambert-St. Louis International Airport. The cross section depicts a large updraft region with the purple and while colors indicative of very large hail.
Figure 19: A north-south oriented radar reflectivity cross section from the KLSX WSR-88D at 0215 UTC when the HP supercell was producing destructive hail in northern St. Louis County including Lambert-St. Louis International Airport. The area of purple on the left side of the image depicts the large hail core extending to the ground across northern St. Louis County.
Figure 20: A 2-panel view at 0235 UTC of the supercell after it had transitioned to a more classic structure and while it was producing a tornado in the Granite City-Pontoon Beach area in Madison County Illinois. A hook echo is clearly evident in the reflectivity image on the left, while the adjacent blue and red colors in the storm-relative velocity image on the right depict a low-level mesocyclone.

NWS
St. Louis, Missouri

The April 10, 2001 Historic Hailstorm and Supercell

Overview:

During the afternoon and evening hours of April 10, 2001, a long-lived high precipitation (HP) supercell thunderstorm traversed portions of Missouri and southwest Illinois producing catastrophic hail damage. The HP supercell produced a swath of large hail approximately 245 miles (395 km) in length and up to 22 miles (35 km)  in width as it moved east through the highly populated Interstate 70 corridor from southeast of Kansas City through St. Louis.    Most of the hail ranged in size from 1.00-3.00 inches in diameter, however south of the largest hail, marginally severe hail (0.75-1.00 inch) also caused considerable damage as it was propelled by 70+ mph downburst (rear flank downdraft) winds. This storm has been named the “Tristate Hailstorm” by Changnon and Burroughs (2003), and is considered the most costly hailstorm in U.S. History with insured losses of $1.5 billion. (*see the authors note below).  Known Missouri insurance claims consist of 120,000 home claims, 65,000 auto claims, and 8,000 commercial claims. It is believed nearly every home and business in northern St. Louis County suffered hail damage.  All of the SUVs parked outside at the Ford Motor Company assembly plant in Hazelwood were damaged (hundreds), while in the adjacent community of Florissant, every home was estimated to have received damage. Twenty-four commercial and military aircraft at Lambert St. Louis International Airport were also damaged. Uninsured losses are unknown. Largely overshadowed by the devastating hail were the tornadoes produced by the HP supercell. This single storm produced a total of 9 weak tornadoes (6 - F1, 3 - F0) with path lengths ranging from 1-10 miles (1.6-16.0 km). The F1 tornado which struck Fulton (southeast of Columbia) destroyed a mobile home producing the first tornado fatality in Missouri since 1994. With $12 million damage reported from the tornadoes, the total damage from the tornadoes paled in comparison to the hail damage.

* Careful and detailed radar analysis (some of which is briefly presented in this event review) reveals that the “Tristate Hailstorm” hailswath as defined by Changnon and Burroughs (2003) was actually the cumulative impact of three distinctly different supercell thunderstorms, rather than one exceptionally long-lived classic supercell. The HP supercell documented in this event review produced the largest hailswath of the three storms, and nearly all of the catastrophic damage. 

If you have questions about this event, or have any photos of the hail or damage that you would be willing to share, please email Lead Forecaster Fred Glass.

Glass, F.H. and M. Britt 2002, The Historic Missouri-Illinois High Precipitation Supercell Of 10 April 2001. Preprints, 21st Conference on Severe Local Storms San Antonio, TX Amer. Meteor. Soc., P3.3.

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SPECI KSZL 102248Z 28036G73KT 220V310 1/4SM +TSRA OVC004 20/18 A2966 RMK TS OHD MOV NE OCNL LTGICCGCC

SPECI KCOU 110014Z 31046G59KT 3/4SM +TSRA BR SQ BKN012 BKN042 OVC080 17/17 A2971 RMK A02 PK WND 33059/0010 WSHFT 2354 RAB08 PRESRR P0030
 

SPECI KSTL 110220Z 30011G37KT 270V340 1SM R30R/1200VP6000FT +TSRA SCT017 SCT046CB BKN050 18/17 A2975 RMK A02 PK WND 30037/0214 WSHFT 0202 TSE14B19RAB14 LTGICCGCAIC TS OHD MOV E GR2 P0050 

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