A Seattle Snowstorm Before Thanksgiving? It Could Happen

SEATTLE, WA — The autumnal equinox is just a week behind us, but it actually might not be too early to start dreaming of snow. Justin Shaw, founder of the popular Seattle Weather Blog, is predicting the season's first snow event will happen on or around November 22.

"Although it's, of course, impossible to accurately predict the date of Seattle's first snowfall, I do think the dice may be loaded a bit toward a mid-to-late November snowfall," Shaw said.

He points to two markers that have allowed for November snowfall in Puget Sound in years past:

• The upcoming winter is projected to be neutral, neither La Niña nor El Niño, which is historically when our region has seen the largest November snow events - in 1985, 1996 and 2003.
• A potential repeat for a "blocking pattern" of high pressure over the Eastern Pacific. Those push the jet stream up north over the artic regions, before moving back down to the Pacific Northwest packed with much cooler air.

That's the same kind of pattern that brought a major snowstorm in February and, Shaw says, one that just repeated in the Northwest last weekend.

"Because it happened in late September, and not late October, snow in Seattle was impossible —but had this pattern occurred even a month later, it probably would have led to some Puget Sound snow."

Shaw said any snow event in November is unlikely to be a "snowpocalypse" on the scale we saw in February, where Seattle was hammered with the most snowfall the city had seen in decades. The highest likelihood for November lands closer to the 1-to-3 inches range. Lowland snow would be possible region-wide, but the highest impact would probably be seen outside Seattle proper.

"While I personally would love for a February repeat, really big snows like that are so rare around here that it's hard to imagine two snowpocalypses in a year," Shaw said.