Weathercatch: How last weekend’s western storm system swept across the U.S.

As a major storm system approached the western United States Friday, a satellite 22,000 miles overhead captured images of its dynamic and moisture-laden pattern. That evening, the storm began making its way across the Pacific Northwest, unleashing an array of winds, snow, rain and freezing rain through the next day.

The system also pushed into northern California, closing stretches of highways and burying mountains in 4 feet of snow. Here in the Inland Northwest, 5 inches of snow fell in Spokane, followed by freezing rain and plain rain. In the normally temperate city of Yakima – nicknamed the Palm Springs of Washington – a half-foot of heavy snow fell. Walla Walla experienced sustained winds up to 40 mph and gusts reaching more than 50 mph.

The storm pulled out of the region late Saturday afternoon, but its work was far from done.

Instead of weakening as it traveled east over the Rocky Mountains, the system picked up strength and kept lumbering eastward. On Monday, nearly 15 million people from Montana to Wisconsin and as far south as Texas faced storm warnings, alerts or watches.

“The storm system will lead to numerous, widespread and impact weather hazards,” the National Weather Service warned.

Sure enough, on Tuesday the sprawling weather system triggered blizzard conditions in South Dakota, Wyoming and Nebraska, and an outbreak of severe thunderstorms that included tornadoes in parts of Oklahoma, Texas and Louisiana.

The system then took aim at the central East Coast before trekking into the Northeast, where it is unleashing winds, rain, ice and snow Thursday.

Several meteorological factors made it possible for the storm that formed off the western coast to plow cross-country to the eastern coast. Initially, the system was driven eastward by a powerful jet stream. During that period, it drew ample moisture from a high-altitude plume of water vapor known as an atmospheric river. As the storm moved farther east, it tapped into moisture from the Gulf of Mexico.

Additionally, the system created spinoff storms fueled by loads of moisture, cold air and atmospheric spin.

The snow that fell over the Inland Northwest Wednesday was courtesy of a new, weak system that traveled from Canada. Heading into this weekend, conditions look to be cool and uneventful. Because model ensembles are rapidly changing and showing a spectrum of outcomes, it’s too soon to predict what next week will bring. Even so, we’re confident it will continue to feel like winter.

Nic Loyd is a meteorologist in Washington state. Linda Weiford is a writer in Moscow, Idaho, who’s also a weather geek. Contact: ldweiford@gmail.com.