Mysterious "dirty rain" falling in Eastern Washington, Oregon

Photo of a dirty, milky substance that has fallen on cars outside the National Weather Service office in Spokane, Wash. on Feb. 6, 2015. (Photo courtesy: National Weather Service)

Update: The Spokane National Weather Service now has a pretty good theory on what caused the milky rain. Updated story here{>}{>}

While it's been a routine, rainy day in Seattle, those over in southeastern Washington and northeastern Oregon have had a strange phenomenon: A dirty, milky rain.

Several reports have come in from Spokane, Walla Walla, Pendleton -- and really across much of that region. The rain has left a dirty residue on cars and has flooded social media over there with people wondering what is causing the odd rain.

So far, the official cause remains a mystery, but officials with the National Weather Service offices in Spokane and Pendleton are looking into it.

The Walla Walla emergency management office posted photos of their area, which show much more of an ashen look to their rain. Their office suggests it all could be ash washing out from an eruption of Volcano Shiveluch in Kamchatka Krai, Russia. Their office says it spewed an ash plume to about the 22,000-foot level in late January and has deposited ash in a widespread area across parts of the Northwest.

The Spokane office of the National Weather Service posted a new photo Friday afternoon showing the cloudy rain that collected in their rain gauge.

"Definitely much cloudier than the typical rain water we see," they wrote on their Facebook page. "We have heard a few theories thus far including; volcanic ash from Mexico or Russia, dust picked up from last night's strong winds, or perhaps ash from last year's wildfires over SE Oregon/SW Idaho. We still don't have a definitive answer."

We'll let you know when we indeed do get more definitive answers