The May 8, 2017 Metro Denver Hailstorm: One of the Costliest in U.S. History (253)

Paul Schlatter, National Weather Service, Boulder, CO

Kari Bowen, National Weather Service



Hailstorms across the High Plains of the U.S. east of the Rocky Mountains are more common than just about anywhere else in the world. In Colorado, the metropolitan Denver area sees anywhere from 11-13 severe hail storms each year. The Denver metro area has also become more vulnerable to the impacts of hailstorms over the past 30 years, pun intended. The reason is rapid population growth; in 1990 the population was around 1.3 million people. Today, the population of metro Denver is estimated to be over 3.5 million people, increasing the damage potential of those hailstorms. On July 11, 1990 a hailstorm packing baseball to softball size hail moved from Estes Park to Boulder and then across a good portion of Denver, causing $1.2B in damages (adjusted for 2017), which was the costliest in U.S. history at the time. On July 20, 2009 a hailstorm across the western part of metro Denver caused $890M adjusted for 2017. Both storms pale in comparison to the hailstorm on May 8, 2017, when up to baseball hail occurred west to east across metro Denver, causing an estimated $2.2B in damages (NCEI estimate). The May 8 hailstorm is one costliest in U.S. history for purely hail damage, similar in cost to the “Tri State Hailstorm” on April 10, 2001. This presentation will detail the near-storm environmental conditions before and during hail fall, the radar and satellite observations, the warning operations in the NWS Boulder office, and finally discuss an unanticipated surprise event that occurred at about the same time as the giant hail. We will also discuss why the damages were so great, and compare/contrast this storm to the other costliest storm in U.S. history.