Weather blog: What is a microburst/downburst?

TWIN FALLS, Idaho (KMVT/KSVT) Storms moved over the Magic Valley around 4 p.m. Saturday afternoon. There was thunder, very little rain, but a whole lot of wind. While I don’t have an accurate estimate on wind speeds during the event, based on damage I saw in my neighborhood alone, I’d guess at least 60 mph if not greater in a few isolated locations. So what caused the damage many of you saw Saturday?

I’ve seen a few people say on social media that we had a “tornado” that’s not true. Given all I saw Saturday afternoon as I shot photos and video for KMVT Local 11 News that night all the trees and damage seemed to be in the same direction. If it were a tornado, we’d have had different types of storms, more rain associated with them and more reports of funnels, which we didn’t have. This was a dry microburst.

A dry microburst comes from a storm that is caused when rain falls from the cloud base, but then evaporates before reaching the ground as it hits drier air near the surface. As this rain evaporates downwards, it cools and accelerates toward the surface. As it hits the surface, it starts to fan out and we will tend to call these straight-line winds. Also, it’s important to note in some of the areas I saw, I’d guess that many of these trees were tipped over from the top down, not just from the side as that air came crashing down to the surface.

Here in the Magic Valley, these events are not only very difficult to predict, but also very difficult see on radar. The radar looked like regular summer-time storms, but the radar beam is a lot higher here than locations closer to Boise and Pocatello where the two radars we use originate from. Because of that, it is nearly impossible to see a storm as it is about to collapse and cause one of these very localized microburst and downburst. Glad to hear that while there was damage, there weren’t many, if any, reports of injuries.




 
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