“When this happens, a storm can form from the moisture up high, but as it creates rain, the rain falls into the very dry air near the ground, and it evaporates, which cools the air.” Precipitation that evaporates before it hits the ground is called virga. This kind of situation happens relatively often in places like Denver,” said Gallus. “For dry microbursts, we know they are more likely when the relative humidity a few thousand feet up in the sky is rather high, but it is much lower (dryer) below that level, especially near the ground. These microbursts are typically driven by both dry air entrainment and water loading.ĭry microbursts usually begin with dry air entrainment due to moisture in the upper levels but eventually turn into wind-driven events with no surface precipitation. Wet microbursts are more common in humid climates where there are plenty of thunderstorms, such as the Southeastern United States. Depending on where you are in the country will determine which type you are more likely to encounter. Microbursts are divided into two basic types: wet and dry. When this cool, dry air is further pulled down by the weight of precipitation, it is called water loading, and this causes the air to drop even faster. William Gallus, a professor of meteorology and numerical weather prediction in the department of geological and atmospheric sciences at Iowa State University, explains this phenomenon: “Cool air is heavier than warm air, so this blob of cold air can plunge toward the ground, and it spreads out rapidly when it hits the ground, kind of like how water explodes sideways when a water balloon is dropped and hits the ground,” he told Live Science.
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