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Microbursts vs. tornados

A couple of weeks ago I saw one patch of lodgepole pine trees on the side of the mountain that had all blown down. The trees were all pointing in the same direction. It was like a giant Paul Bunyon had chopped down a bunch of trees all at once with a huge ax.

The downed trees made me wonder: What had caused only that one patch of timber to fall while all of the other trees around it were still standing?

Sometimes trees are blown over by what’s known as a microburst. A microburst is a strong downward draft of wind. That wind can reach 60 mph as it speeds to earth. When the wind hits the ground it’s like water splashing out in all directions. When the wind splashes it may move even faster, creating straight winds that can blow at speeds up to 120 mph.

Seems like either one of those speedy winds could take down a shallow-rooted lodgepole pine.

Microbursts come in two styles — ones that are wet, which are more common in the southeastern portion of the United States; and ones that are dry, which are more likely to be found in mountainous areas like Montana.

Strong summer thunderstorms can create microbursts by holding warm air up in the clouds. If that warm air is quickly cooled, it can fall to the earth as a microburst. That’s because cool air is heavier than warm air.

Tornadoes will also sometimes occur in the mountains, but it’s not very common. One tornado hit high in the mountains of northwestern Wyoming  at about 10,000 feet  in 1987. The winds in that storm blasted down trees by blowing at about 200 mph.

Usually tornadoes won’t develop in the mountains because the air is cooler. Tornadoes need lots of warm, wet air to get started.

— Brett French,

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