In early February, parts of the Pacific Northwest experienced what was described as "milky rain," precipitation characterized by suspended silty particulates. Once evaporated, the rain left behind a chalky residue.

The milk rain befuddled local meteorologists -- though that didn't stop them from offering a range of theories.

But now scientists have an official explanation for, or better yet, an official source of the milk rain: a shallow saline lake in Oregon, called Summer Lake.

After testing rain samples and examining local wind patterns from the time period, scientists determined the most likely explanation was that a series of storms churned up the salty sediments of Summer Lake. Weather carried the milky moisture several hundred miles to the northwest, dropping it on portions of Idaho, Oregon and Washington along the way.

"A lot of sodium was in that milky rain," Kent Keller, a hydrochemist at Washington State University, explained in a press release. "The chemistry is consistent with a saline source from a dry lake bed."

The researchers tested alternative explanations and ruled them unlikely -- like suggestions that the milky sediment was ash from nearby forest fires or faraway volcanic eruptions, or Nevadan dust storms.

"At first we suspected it was related to wind erosion of landscapes that had previously burned, but the wind trajectory analyses didn't add up," admitted Brian Lamb, head of Washington State's Laboratory for Atmospheric Research.

A similar episode of milky rain was reported in New Mexico seven years ago. The rain was also linked to a nearby salty lake.