Published: June 27,2017
Torrential downpours are frequently associated with thunderstorms, but there’s another breed of thunderstorm in the western states that produces little or no rain at all and yet presents multiple hazards.
These so-called dry thunderstorms are accompanied by lightning, but little, if any, rain from them reaches the ground. Dry thunderstorms are most common in the western United States late in spring and into early summer when monsoonal moisture is absent in the region.
(MAP: Lightning Strikes Right Now)
Rain evaporates before reaching the ground in a dry thunderstorm, but lightning is still a major hazard.This is because the air is dry near the earth's surface, but ample moisture aloft can still aid in the formation of a thunderstorm if there is a source of lift in the atmosphere. As raindrops from thunderstorm clouds encounter the dry air, they evaporate. In the world of meteorology, this is referred to as virga.
Lightning strikes from dry thunderstorms are particularly hazardous in the West because they can ignite wildfires since no rain is wetting the vegetation below. The dry fuels are a prime source for wildfire development.
In the red square are several dry lightning strikes (blue and red dots) detected in the West on June 20, 2017. Little, if any, precipitation occurred in the same general area. Precipitation is shown in green/brown contours elsewhere in the Lower 48.Fire weather forecasters also classify storms that produce very light rain amounts at the earth's surface as dry thunderstorms. This occurs when the meager amount of rain that falls has no effect on hampering the spread of a wildfire after lightning ignites it, according to the National Weather Service.
In addition to sparking new fires, strong blasts of wind from dry thunderstorms can be a nightmare for firefighters battling an ongoing wildfire because of potential for shifting winds.
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More than 10,280 lightning-sparked fires are reported in the United States annually, according to the National Interagency Fire Center. About 58 percent of those occur in the western states. It's unknown how many of those were caused by dry thunderstorms.
Dry thunderstorms present a hazard to those participating in outdoor activities. With no rain falling from a storm, campers and hikers may be unaware of nearby lightning.
As always, seek shelter if you are outdoors and hear thunder with or without rain falling. This means lightning is nearby and you could be in danger.
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