The science behind microbursts

ST. JOSEPH, Mo. (News-Press NOW) -- Have you ever been driving and noticed a thunderstorm pouring in just one spot, while it’s completely dry everywhere else? Odds are, we all have -- as localized downpours are common during warmer months of the year.

On occasion, otherwise garden-variety thunderstorms can also contain a concentrated burst of strong to damaging wind gusts. This higher level of thunderstorm intensity, taking place over a small area, is called a microburst.

Microburst events can occur year-round, but they’re especially common in the summer when heat and humidity generate high levels of atmospheric instability. One of the necessary ingredients for the development of vigorous thunderstorms, capable to produce microbursts.

Within a thunderstorm cell, a microburst is a small, concentrated column of air that rapidly sinks and slams into the ground. Once it hits, the wind spreads out in all directions. Microbursts are technically a type of downburst, just on a smaller scale, typically spanning less than 2.5 miles in width.

Microbursts also come in two separate subtypes, wet and dry. A dry microburst contains little to no precipitation, while a wet microburst is accompanied by heavy rain and sometimes hail.

Wet microbursts are more common in Northwest Missouri and Northeast Kansas, although dry microbursts can also take place locally, given the right conditions.

Here’s how they form: High up in a thunderstorm, rain starts to fall and passes through a layer of drier air. As it falls, it evaporates, and that cools the air down quickly. That cold, dense air becomes much heavier than the air around it and sinks fast. When it reaches the ground, it has nowhere to go—so it spreads out in a violent burst of wind.

These events are short-lived, often lasting just a few minutes, but wind speeds can exceed 100 mph. That’s equivalent to an EF1 tornado.