The National Weather Service is trying to determine the cause of a mysterious "milky rain" that left residue on cars, clothing, and more in Washington, Oregon and Idaho on Friday.
A rainstorm originating in the Pacific Ocean moved through the area Friday, prompting reports of the milky residue in more than 15 cities,
USA Today reported.
The light gray raindrops likely were caused by volcanic ash from Volcano Shiveluch in Kamchatka Krai, Russia, which erupted in January, the Walla Walla County emergency management staff posted on its Facebook page.
Weather Service forecaster Greg Koch told
ABC News that it is not uncommon to see muddy rainfall in summer months, but added "what was so unusual about this was not only that it occurred in the winter time, but it was a milky white or gray, which is very different than what we have around here."
Other speculation includes a volcano in Mexico and ash from 2014 wildfires over Oregon and Idaho.
The Weather Service office in Spokane is having a sample of the rain tested and is requesting samples from other areas that experienced the milky rain.
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