Chances are you have witnessed many thunderstorms in your life, heard the unmistakable crack of thunder, seen the bright flashes of lightning, and maybe have fallen asleep to the ever familiar sound of the rain tapping against your window. But unless you live in an arid climate, you have likely not experienced, or maybe even heard of, dry thunderstorms.
Dry thunderstorms are thunderstorms where little to no precipitation makes it to the surface. This can be common in thunderstorms that occur in deserts or areas where the lower atmosphere is very dry. Dry thunderstorms do produce rain, however, as the rain falls through dry layers of air beneath the cloud base, much of the rain then evaporates. The falling rain that doesn’t make it to the ground is also known as virga. As this rain evaporates, it cools the air beneath it causing that air to become “heavier” than the surrounding warmer air. This air can rapidly fall and cause strong winds to fan out at the surface. This phenomenon is also known as a dry microburst.
Dry thunderstorms are also an important phenomenon when it comes to fire weather. Since little precipitation makes it to the surface, dry areas experiencing dry thunderstorms are more susceptible to fire ignition by lightning strikes. In a typical thunderstorm, the rainfall can prevent lightning from igniting fires. For fire weather purposes, dry thunderstorms can be classified as producing less than .1 inches of rain, although this threshold can depend on how dry the area is as well as the amount of vegetation in the area. Both of these factors can determine how much rain is necessary to properly wet the surface and prevent lightning-caused fire ignition.
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©2019 Meteorologist Stephanie Edwards