Scientists at Washington State University say they have the final word on the cause of the strange milky rain that left white splotches on cars and windows in the Tri-Cities on Feb. 6.
As suspected for the past couple of months, it was the result of a severe wind storm stirring up sand and soil at Oregon’s remote Summer Lake, they said.
Researchers at Washington State University analyzed weather data and samples collected by the Benton Clean Air Agency to reach that conclusion.
“A lot of sodium was in that milky rain,” said WSU hydrochemist Kent Keller. That’s consistent with the dry ground near shallow, saline Summer Lake about 250 miles southwest of the Tri-Cities.
The chemical composition and weather patterns ruled out other leading theories — ash from a distant volcanic eruption, dust storms in the Middle East, ashy debris stirred up from 2014 wildfires in the Northwest and fallout from a Nevada dust storm.
The Benton Clean Air Agency said in late February that the samples it collected and tested included sodium, silicon and trace amounts of aluminum, potassium, magnesium, calcium, iron and manganese. There also was a trace of organic carbon.
Its concern was to rule out a health risk. After concluding that nothing in the sample suggested a risk, it left further analysis to WSU.
“At first we considered it was related to wind erosion of landscapes that had previously burned, but the wind trajectory analysis didn’t add up,” said Brian Lamb, who runs the WSU Laboratory for Atmospheric Research.
Nor did the trajectories look like they could have been feasible when traced to two volcanic eruptions shortly before the milky rainfall, one in Russia and the other in Mexico, said WSU meteorologist Nic Lloyd.
But the air flow from the south did arc over Summer Lake. Wind gusts of 60 mph had stirred up dust there the night before the milky rainfall to the north.
“That would have been powerful enough to lift a good-size dust plume,” Lloyd said. Rain from Hermiston to the Tri-Cities to Spokane then washed the dust out of the air, depositing it in gray and white drops.
“It was like a big dust storm blew through, but the weird part was there was no wind or dust in the air that I noticed,” said Mike Savage of Kennewick, in February, after finding his Ford F-150 pickup covered with milky rain spots.
A similar event was recorded about seven years ago in southern New Mexico, according to WSU. Dust that was high in sodium was carried from a dry, salty lake bed 120 miles away before it was deposited on the ground.