By Nic Loyd, WSU meteorologist, and Linda Weiford, WSU News

weathercatch(2) (2)SPOKANE, Wash. – On Nov. 17, a giant windstorm roared through the region to a balmy high temperature of 54 degrees. A little more than a week later, temperatures plunged to 7 degrees and we saw barely any wind at all.

Call it weird, call it flip-floppy. In a relatively short time span, the weather changed dramatically across eastern Washington while delivering unusual conditions to boot.

By now, many of you know that the windstorm that downed hundreds of trees and caused a record-breaking number of power outages was historic because of its hurricane-force strength.  Gusts clocked as high as 71 mph in Spokane and 76 mph in the small farming town of Kahlotus, Wash., 98 miles away.

wind-storm,-then-frost
Winds that downed power lines and trees, left, gave way to still air and frigid temperatures to close out November.

But how the system evolved is also historic. Windstorms that strike Washington typically mature in the northern Pacific Ocean and weaken as they move across the state. Not our November storm, which did just the opposite – revving up strength while moving east and hitting its peak by the time it reached the Inland Northwest.

That storm system was unusual, but so too was the warm temperature. As winds sheared rooftops and uprooted towering trees, the mercury climbed to 54 degrees. Consider that the average high for that date is 40 degrees.

Roughly a week after the windstorm – as many residents continued to clean up its mess – frigid and near-windless conditions descended upon the area. Freezing fog, plenty of frost and an air stagnation advisory issued by the National Weather Service joined the mix.

“. . . due to limited movement of an air mass across advisory area, pollution has the potential to increase to dangerous levels,” the agency warned.

This air stagnation, like a dirty blanket in the sky, was caused by a temperature inversion that occurred when an upper layer of warm air trapped colder air beneath it. With weak winds, the inversion stayed put for seven days.

And yes, it got cold. We saw a frosty low of 7 degrees on Nov. 28 and a measly high of 20 degrees the next day. Both stand at 18 degrees below normal for this time of year.
So what’s next? For December, it looks like another “unusual” weather condition awaits us: unseasonably warm. Due to an escalating El Nino weather pattern in the tropical Pacific, above-normal temperatures are expected across most of the northern U.S.

 

Weathercatch is a bimonthly column published in the Spokesman Review