See Mysterious 'Milky Rain' on Cars in the Northwest

— -- Officials in the Northwest are investigating mysterious, milky-looking raindrops that left residue on cars, jackets and phones in the region.

The National Weather Service in Spokane, Washington said cars at their office were covered in dirty, milky raindrops on Friday.

The milky rain was reported in about a dozen cities in the Northwest, including Ritzville, Walla Walla and Coeur d'Alene.

Weather Service forecaster Greg Koch told ABC News today that a muddy, brown-tinted rain is common during summer storms, but "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."

Koch said the mysterious rain may have been caused by "a strong wind event in Northwest Nevada Thursday night, which continued into Friday, and that caused a lot of blowing dust in the Reno area and points north and east of there."

Other theories for where the residue came from include "volcanic ash from Mexico or Russia... or perhaps ash from last year's wildfires over SE Oregon/SW Idaho," the Weather Service said on Facebook, adding that they still "don't have a definitive answer."

The Weather Service said it reached out to other agencies to see if they have collected samples for testing.