What is a microburst? Everything you need to know

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After a drier and hotter-than-normal trend hit Arizona in midsummer, the state is ushering in a wetter end to the monsoon with thunderstorms, hail, strong winds and heavy rain — as well as small blasts — sweeping through parts of the valley.

In Arizona, you may have seen a small explosion without knowing what it was. In short, this phenomenon is a column of fast air rushing over a small area, and it occurs when a pocket of cold air forms within a thunderstorm.

Cold air is denser. When this pocket of air is concentrated enough, it becomes heavier than the air around it, causing it to fall like a bomb; Usually over an area smaller than 2.5 miles in diameter.

According to the Weather Service, small explosions can generate winds of up to 150 mph and cause more surface damage than a tornado and, in some cases, can be life-threatening.

Here’s everything you need to know about interesting weather occurrences and how to stay safe.

Are micro-eruptions common in Arizona?

Alex Young, a meteorologist with the National Weather Service in Phoenix, said small explosions occur frequently in the state.

“With any thunderstorm activity, especially during the monsoon season, a downburst or microburst is common,” he said.

Microbursts can also come with heavy rain and sometimes hail, which are called wet microbursts. Young said dry microbursts are the most common type in Arizona, but more wet minibursts can be seen during the summer months.

What happens during a microburst?

Every thunderstorm forms with an updraft and a downdraft, according to Young. The updraft drives a thunderstorm by quickly pulling in moisture, and the downdraft is where precipitation from the storm falls.

During small eruptions, moisture and air pulled in by the updraft become denser as they are pulled upward, Young said. The updraft will then reach a point where it condenses into water droplets and sometimes hailstones that get stuck in the upper parts of the thunderstorm.

As the updraft continues to bring in more water that later condenses, the updraft weakens, at which point it is no longer able to hold the concentrated air and water in the storm, causing this core to sink to the ground.

In a dry environment, such as in Arizona, these water droplets are likely to evaporate again in the storm. This evaporation cools the air, increasing the downdraft effect on the ground.

“That’s why small, dry eruptions are usually more common in Arizona, and they can have a big impact, because that evaporative cooling process is going to accelerate that downdraft to make it stronger,” Young said.

How long do micro-eruptions last?

The initial strong boost of winds could last 5 to 20 minutes, Young said. He added that the stormy winds sweeping through the area could last for up to an hour.

“Actually, that initial boost is usually the worst, because that’s going to be the strongest winds when a small explosion occurs,” Young said.

What are the risks of micro explosion?

The biggest threat that can come with a small explosion is wind, Young said.

Even if the area is not directly affected by the small explosion, Young said the winds blowing over the place will spread to neighboring areas, resulting in strong, gusty winds.

Even after winds hit the ground, they can spread at speeds of about 60 mph, although that can vary depending on the strength of the blast and humidity levels, among other conditions, Young said.

Damage in areas directly affected by the first shot of air could be more severe, according to the weather service. The wind speeds of small blasts are equivalent to an EF1 tornado and can do significant damage to residences and down a large number of trees in a matter of minutes.

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Monsoon winds blow down utility poles in Phoenix near 16th and 20th Streets

Twelve power poles between 16th and 20th Streets in Phoenix were among the damage seen on September 13, 2023, after a night of gusty winds and heavy rain.

Rob Schumacher, Arizona Republic

The weather service advised residents to take severe thunderstorm warnings as seriously as tornado warnings.

Both types of small explosions, wet and dry, generate strong winds, and both can be equally dangerous, Young said.

However, the effects can be different. Some other risks that can come with wet microbursts are hail and heavy rain, which can increase the risk of flooding. On the other hand, small dry explosions can also produce localized dust above accelerating winds.

“Especially if you have a complex cluster of thunderstorms, and all the small explosions combined together, it can create dust amplification that typically ends up arriving in metro Phoenix from southern and eastern Arizona,” Young said.

What are the signs of a mini-explosion?

Although small explosions are difficult to predict and occur quickly, people in the vicinity of a thunderstorm can see heavy explosions coming if they see heavy rain concentrated in the distance.

“This is a way that you can monitor the weather and try to at least identify something that could potentially happen in your area in terms of a microburst,” Young said.

According to the Weather Service, ideal conditions typically occur during hot, humid summer afternoons.

Young advised residents to check the weather frequently and stay aware of thunderstorm activity.

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