Dear Tom,

I recently heard the term “tsunami cloud”. What is it?
Thanks, Scott Bentley Woodstock

Dear Scott,
A tsunami cloud, or a cloud tsunami is really another name for a shelf cloud or a roll cloud, both ominous-looking clouds that can develop ahead of approaching thunderstorms. A shelf cloud is a low-level wedge-shaped cloud associated with the outflow or gust front from the approaching thunderstorm. It a part of the approaching storm’s cloud base and a rising motion is visible in the storm’s leading edge. The underside of the shelf cloud usually appears ragged, tattered, and turbulent. Roll clouds also precede thunderstorms but are detached from the storm’s base. They appear to be rolling along a horizontal axis. Both roll clouds and shelf clouds can occur anywhere there is thunderstorm activity.