By Linda Weiford, WSU News
PULLMAN, Wash. – The mysterious “milky rain” that hit parts of the Pacific Northwest last Friday was the result of a rarely seen weather phenomenon that began near an ancient saline lake nearly 500 miles away, according to Washington State University meteorologist Nic Loyd.
A meshing of independent weather systems that appears to have started in a remote area of southern Oregon ultimately caused dirty-white-colored raindrops to fall in eastern Washington and northeast Oregon, he said.
“It was an unusual convergence of weather factors that set up the event. Drifting ash from a volcanic eruption would have been easier to figure out,” said Loyd of WSU’s AgWeatherNet.
Nevada trajectory unlikely
The National Weather Service received reports Friday afternoon of ashy debris coating vehicles and windows as a rainstorm moved into more than 15 cities, including Spokane and the Tri-Cities in Washington and Hermiston, Ore. While the ash-like substance has not yet been scientifically confirmed, it’s believed to be from a dust storm clocking 60 mph winds that struck Summer Lake on Thursday night, according to the weather service.
Thanks to an exceptional parade of weather events, light-colored dust from Summer Lake’s alkali beds appears to have traveled – distance-wise – the equivalent of an eight-hour car ride before landing, said Loyd.
Originally, a large storm that hit northwest Nevada was blamed for the unusual-colored rainfall.
“But the trajectory just didn’t add up,” said meteorologist Mary Wister of the weather service’s Pendleton, Ore., office. “The wind direction would have carried the dust into western Montana, not in your direction.”
Winds hurl Oregon dust
Here’s what appears to have happened instead:
First, hurricane-force winds whipped across the Summer Lake region in south central Oregon, “lofting dry, light-colored sands and soils into the air,” Loyd explained. Wister said wind gusts there reportedly lasted throughout the night.
Next, strong southerly winds transported the sand and soil particles northward.
“Had the winds not been so strong or constant, the dust plume would have dispersed before it got here,” said Loyd. “As it was, it was able to travel a large distance in less than 12 hours.”
Finally, when the plume arrived, a rainstorm passing through pockets of Washington and Oregon drove the debris downward in the form of milky raindrops.