Dear Tom,
Are orographic thunderstorms common in the US? Are they ever severe?
Thanks,
Jake Doss, Morris

Dear Jake,

Orographic thunderstorms are common in the U.S, occurring in areas where moisture-laden winds are forced upward as they encounter mountain ranges. While the vast majority of these storms are not severe, they can be prolific precipitation producers and account for excessive annual rainfall on the windward slopes of mountains. Prime examples are in portions of Hawaii and the Pacific Northwest. These type of storms tend to be slow-moving, and the heavy rainfall can trigger flash flooding. On occasion, they can also produce hail, intense lightning, and even brief tornadoes. In June 1972 orographic thunderstorms produced devasting flash floods in the Rapid City, South Dakota area killing 238 and injuring several thousand people.