What is a Microburst?

It isn't really a tornado.

Formation of a Microburst
Judy Hedding

Arizona's monsoon brings summer thunderstorms, dust storms, and occasional microbursts. Each summer these weather patterns result in dangerous situations and damage.

What is a Microburst?

A downburst is defined as a strong downdraft with an outrush of damaging winds on or near the ground. If the swath is less than 2.5 miles, it is called a microburst.

A microburst is a small, very intense downdraft that descends to the ground resulting in a strong wind divergence. The size of the event is typically less than 4 kilometers across. Microbursts are capable of producing winds of more than 100 mph causing significant damage. The lifespan of a microburst is around 5-15 minutes. There are wet microbursts and dry microbursts.

When rain falls below cloud base or is mixed with dry air, it begins to evaporate and this evaporation process cools the air. The cool air descends and accelerates as it approaches the ground. When the cool air approaches the ground, it spreads out in all directions and this divergence of the wind is the signature of the microburst. In humid climates, microbursts can also generate from heavy precipitation.

Microbursts are quick-hitting events and are extremely dangerous to aviation. Microbursts are sub-classified as dry or wet microbursts, depending on how much rain accompanies the microburst when it reaches the ground. If the swath is more than 2.5 miles, it is called a macroburst. Macrobursts last longer than microbursts.

Is a Microburst a Tornado?

No, but there are some similarities. There is often a lot of wind that develops very quickly. Different than a microburst, though, wind flows into a tornado and not out, like it does in a downburst. Tornados also result in that swirling wind that you see in most movies and videos, which is not necessarily present during a microburst. Microbursts are much more common than tornadoes, and it is very rare to have a tornado in the Phoenix area even during the summer monsoon.

Do Microbursts Cause Damage?

Yes, they certainly can. Tornado damage often has a chaotic appearance, with larger uprooted trees often crossing each other, while microburst damage often leaves them laid in the same direction or flattened out. 

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