Severe thunderstorm broke out across Denver and the surrounding metro area and produced large damaging hail, strong winds, heavy rain and flash flooding.  Large hail up to baseball size, caused extensive property damage to cars, homes and businesses across a large part of Denver and the western suburbs including Arvada, Lakewood and Wheat Ridge. According to the Rocky Mountain Insurance Agency Association, the storm was Colorado���s most expensive insured catastrophe, around $2.3 billion.  It also ranked as the second costliest hailstorm in U.S. history.  The group estimated more than 150,000 auto insurance claims and 50,000 homeowner insurance claims would be filed.  Businesses and homes sustained holes in siding along with broken windows and torn screens. Severe thunderstorm producing large hail, strong winds and heavy rain impacted areas around Greeley as well.
The high cost incurred from the storm was due to a number of factors including:  the size of the hail, the densely populated area, the time of day, the escalating costs to repair high-tech cars, and more expensive homes.  Colorado Mills Mall in Lakewood was severely damaged after hail busted skylights and caused flooding inside stores.  The common areas and tenant spaces suffered substantial water damage.  Extensive damage to electrical systems, mechanical systems, including HVAC and lighting, kept the mall closed until November 2017.  In Lakewood, the loss in sales tax was projected to be about $350,000 per month, which was 3 to 4 percent of the city's monthly budget.  Prestige Imports in Lakewood which sells Audis and Porches,  estimated 250 to 300 vehicles were impacted by the storm.  Some of those vehicles were valued at nearly $200,000 each.
Significant damage was reported at Lutheran Medical Center after a hailstorm tore through Wheat Ridge.  The hospital building and some of the medical office buildings sustained broken windows.  The storm also hit the office of the Colorado Bureau of Investigation in Lakewood. The offices were flooded, several cubicles destroyed, and even some ceiling tiles fell off.  The storm damage prompted school officials to close all thirteen Adams 12 Five Star schools in Commerce City and Beach Court Elementary school in Denver. Most of the schools in the Adams 12 Five Star District are at least 50 years old and sustained flood damage.  Large hail damaged an apartment building near Regis University, shattered windows and punctured the siding on the west-facing side of the building.   Severe thunderstorms also produced large hail across parts of Larimer, Lincoln and Weld Counties.
Hail and heavy rain clogged drains and caused flash flooding throughout Greeley. Up to three feet of water covered the roadway near U.S. 34 and U.S. 85.  Flooding was reported throughout Greeley.  The Greeley Fire Department received 30 calls of flooding.  Firefighters helped several residents get out of garden level apartments that had flooded.  Several other businesses and buildings suffered flood damage, including Greeley City Hall and an apartment complex in Evans.  The Greeley Mall was extensively damaged when water poured into the mall from the roof and debris inundated the main floor.  The Frontier Academy Elementary School was also flooded, with administrators canceling classes the following day to clean up the damage.  Windsor-Severance Fire Protection District had multiple reports of lightning strikes, including one that hit near Windsor Middle School and set off the school's fire alarms.

Hail in JEFFERSON, COLORADO
From 08-MAY-17 13:30:00 to 08-MAY-17 13:30:00 (MST-7)
Location: IDLEDALE
Magnitude: 1.00 
Reported by: Trained Spotter

Hail in JEFFERSON, COLORADO
From 08-MAY-17 13:40:00 to 08-MAY-17 13:40:00 (MST-7)
Location: PLEASANT VIEW
Magnitude: 1.25 
Reported by: Trained Spotter

Hail in JEFFERSON, COLORADO
From 08-MAY-17 13:48:00 to 08-MAY-17 13:48:00 (MST-7)
Location: LAKEWOOD
Magnitude: 1.25 
Reported by: CoCoRaHS

Hail in JEFFERSON, COLORADO
From 08-MAY-17 13:50:00 to 08-MAY-17 13:50:00 (MST-7)
Location: PLEASANT VIEW
Magnitude: 2.00 
Reported by: Trained Spotter

Hail in JEFFERSON, COLORADO
From 08-MAY-17 13:52:00 to 08-MAY-17 13:52:00 (MST-7)
Location: LAKEWOOD
Magnitude: 1.00 
Reported by: CoCoRaHS

Hail in JEFFERSON, COLORADO
From 08-MAY-17 13:52:00 to 08-MAY-17 13:52:00 (MST-7)
Location: GOLDEN
Magnitude: 1.75 
Reported by: Trained Spotter

Hail in JEFFERSON, COLORADO
From 08-MAY-17 13:52:00 to 08-MAY-17 13:52:00 (MST-7)
Location: EDGEWATER
Magnitude: 2.00 
Reported by: CoCoRaHS

Hail in JEFFERSON, COLORADO
From 08-MAY-17 13:55:00 to 08-MAY-17 13:55:00 (MST-7)
Location: LAKEWOOD
Magnitude: 1.00 
Reported by: Trained Spotter

Hail in DENVER, COLORADO
From 08-MAY-17 14:05:00 to 08-MAY-17 14:05:00 (MST-7)
Location: DENVER
Magnitude: 1.00 
Reported by: CoCoRaHS

Hail in JEFFERSON, COLORADO
From 08-MAY-17 14:05:00 to 08-MAY-17 14:05:00 (MST-7)
Location: WHEAT RIDGE
Magnitude: 1.75 
Reported by: CoCoRaHS

Hail in ARAPAHOE, COLORADO
From 08-MAY-17 14:15:00 to 08-MAY-17 14:15:00 (MST-7)
Location: (BKF)BUCKLEY AIR FORCE BASE
Magnitude: 1.25 
Reported by: Trained Spotter

Hail in DENVER, COLORADO
From 08-MAY-17 14:15:00 to 08-MAY-17 14:15:00 (MST-7)
Location: DENVER
Magnitude: 1.00 
Reported by: Public

Hail in ADAMS, COLORADO
From 08-MAY-17 14:27:00 to 08-MAY-17 14:27:00 (MST-7)
Location: BRIGHTON
Magnitude: 1.00 
Reported by: Trained Spotter

Hail in DENVER, COLORADO
From 08-MAY-17 14:27:00 to 08-MAY-17 14:27:00 (MST-7)
Location: DENVER
Magnitude: 1.50 
Reported by: Public

Hail in JEFFERSON, COLORADO
From 08-MAY-17 14:30:00 to 08-MAY-17 14:30:00 (MST-7)
Location: GOLDEN
Magnitude: 2.00 
Reported by: Trained Spotter

Hail in WELD, COLORADO
From 08-MAY-17 14:30:00 to 08-MAY-17 14:30:00 (MST-7)
Location: WINDSOR
Magnitude: 1.00 
Reported by: CoCoRaHS

Hail in ADAMS, COLORADO
From 08-MAY-17 14:45:00 to 08-MAY-17 14:45:00 (MST-7)
Location: WESTMINSTER
Magnitude: 1.00 
Reported by: Trained Spotter

Hail in JEFFERSON, COLORADO
From 08-MAY-17 13:45:00 to 08-MAY-17 13:45:00 (MST-7)
Location: EDGEWATER
Magnitude: 1.75 
Reported by: CoCoRaHS

Flash Flood in WELD, COLORADO
From 08-MAY-17 16:00:00 to 08-MAY-17 19:00:00 (MST-7)
Location: PECKHAM
Flood cause: Heavy Rain
Property damage: 500.00K
Crop damage: 50.00K
Reported by: Law Enforcement

Heavy rain combined with torrential hail, clogged drains and caused flash flooding throughout Greeley.  The intersection near U.S. 34 and U.S. 85 was inundated with up to 3 feet of water.  Firefighters rescued several residents from garden level apartments that had flooded.   Several businesses and buildings suffered flood damage, including Greeley City Hall and an apartment complex in Evans. The Greeley Mall was extensively damaged as water poured into the mall from the roof and debris inundated the main floor.  The Frontier Academy Elementary School was also flooded, with administrators canceling classes the following day.

Lightning in WELD, COLORADO
From 08-MAY-17 15:40:00 to 08-MAY-17 15:40:00 (MST-7)
Location: GREELEY
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Windsor-Severance Fire Protection District had multiple reports of lightning strikes, including one that hit near Windsor Middle School and set off the school's fire alarms.

Hail in JEFFERSON, COLORADO
From 08-MAY-17 13:53:00 to 08-MAY-17 13:53:00 (MST-7)
Location: PLEASANT VIEW
Magnitude: 1.75 
Reported by: Trained Spotter

Hail in ARAPAHOE, COLORADO
From 08-MAY-17 13:57:00 to 08-MAY-17 13:57:00 (MST-7)
Location: (BKF)BUCKLEY AIR FORCE BASE
Magnitude: 1.50 
Reported by: Trained Spotter

Hail in JEFFERSON, COLORADO
From 08-MAY-17 14:00:00 to 08-MAY-17 14:00:00 (MST-7)
Location: ARVADA
Magnitude: 0.88 
Reported by: NWS Employee

Hail in LARIMER, COLORADO
From 08-MAY-17 14:01:00 to 08-MAY-17 14:01:00 (MST-7)
Location: KELIM
Magnitude: 1.50 
Reported by: Trained Spotter

Hail in JEFFERSON, COLORADO
From 08-MAY-17 14:03:00 to 08-MAY-17 14:03:00 (MST-7)
Location: EDGEWATER
Magnitude: 1.75 
Reported by: COOP Observer

Hail in DENVER, COLORADO
From 08-MAY-17 14:04:00 to 08-MAY-17 14:04:00 (MST-7)
Location: DENVER
Magnitude: 2.00 
Reported by: NWS Employee

Hail in JEFFERSON, COLORADO
From 08-MAY-17 14:04:00 to 08-MAY-17 14:04:00 (MST-7)
Location: EDGEWATER
Magnitude: 2.50 
Reported by: COOP Observer

Hail in JEFFERSON, COLORADO
From 08-MAY-17 14:05:00 to 08-MAY-17 14:05:00 (MST-7)
Location: EDGEWATER
Magnitude: 2.75 
Property damage: 2.30B
Reported by: Trained Spotter

The estimated damage is for the entire episode.

Hail in DENVER, COLORADO
From 08-MAY-17 14:06:00 to 08-MAY-17 14:06:00 (MST-7)
Location: DENVER
Magnitude: 2.50 
Reported by: Trained Spotter

Hail in JEFFERSON, COLORADO
From 08-MAY-17 14:09:00 to 08-MAY-17 14:09:00 (MST-7)
Location: EDGEWATER
Magnitude: 1.00 
Reported by: Trained Spotter

Hail in DENVER, COLORADO
From 08-MAY-17 14:15:00 to 08-MAY-17 14:15:00 (MST-7)
Location: DENVER
Magnitude: 1.00 
Reported by: Trained Spotter

Hail in DENVER, COLORADO
From 08-MAY-17 14:16:00 to 08-MAY-17 14:16:00 (MST-7)
Location: DENVER
Magnitude: 1.75 
Reported by: Trained Spotter

Hail in ARAPAHOE, COLORADO
From 08-MAY-17 14:20:00 to 08-MAY-17 14:20:00 (MST-7)
Location: DEER TRAIL
Magnitude: 2.00 
Reported by: Trained Spotter

Hail in DENVER, COLORADO
From 08-MAY-17 14:20:00 to 08-MAY-17 14:20:00 (MST-7)
Location: DENVER
Magnitude: 1.75 
Reported by: COOP Observer

Hail in ADAMS, COLORADO
From 08-MAY-17 14:25:00 to 08-MAY-17 14:25:00 (MST-7)
Location: FEDERAL HGT
Magnitude: 1.00 
Reported by: Trained Spotter

Hail in JEFFERSON, COLORADO
From 08-MAY-17 14:29:00 to 08-MAY-17 14:29:00 (MST-7)
Location: LAKEWOOD
Magnitude: 2.00 
Reported by: Public

Hail in WELD, COLORADO
From 08-MAY-17 14:47:00 to 08-MAY-17 14:47:00 (MST-7)
Location: JOHNSTOWN
Magnitude: 1.00 
Reported by: NWS Employee

Hail in LINCOLN, COLORADO
From 08-MAY-17 15:50:00 to 08-MAY-17 15:50:00 (MST-7)
Location: (LIC)LIMON ARPT
Magnitude: 1.25 
Reported by: Storm Chaser