Why We Don't Get Much Snow, But Plenty of Ice with Snow

Nov 29, 2013

Western Washington winters are relatively mild. We rarely see snow in the lowlands. But when it does snow, things freeze over in a hurry. 

Why does that happen? It has to do with our mild temperatures, says KPLU Weather expert Cliff Mass.

Snow: Why So Rare, and Why So Hard to Predict? 

Local conditions are stacked against snow, says Mass, and that's what makes snow so hard to forecast; the conditions have to be just so.

“It’s really hard to get snow here. It’s very easy for us to be warm and wet,” said Mass, who teaches atmospheric sciences at the University of Washington. “Normally, these weather systems come off the Pacific Ocean, and that’s relatively warm. The temperature is about 50 degrees, so it’s very easy to be mild and relatively warm, and have nice rain.”

Sometimes we see cool and dry weather when high pressure builds inland. In those cases, we might see fog followed by clear skies, but still no snow.

“To get snow, you’ve got to be cold and wet at the same time,” said Mass. “And that’s extraordinarily hard to do around here, and that’s very hard to forecast.”

And Yet, So Much Ice—Why?

We may be too warm to see much snow, but when we do get snow, we tend to be much icier than most places.

Here's why that is, says Mass. Our mild winter days keep the temperature of the roads, as well as the soil beneath the surface, above freezing.

“So if we get some snow falling on these road surfaces, it tends to melt, so we tend to get this slushy stuff. And then, if cold air comes in behind it—if an Arctic Blast from British Columbia comes over—it’s cold enough to freeze that slushy mixture into solid ice,” said Mass.

We’ve seen this happen times over, says Mass, including during the storm of December 2008.

“We had snow melted, it got cold, then we had that ice layer that was almost impossible to take off,” he said.

How to Stay Safe When Snow Hits

Since snow is hard to predict, and icy roads are a known danger around here, Mass recommends several websites to stay up-to-date when snow is in the forecast, as it is this weekend

Snowwatch: Latest forecasts from the Weather Service for the Seattle area

Snoqualmie Pass Report

Stevens Pass Report

Weather with Cliff Mass: Latest updates form Mass possibility of snow this weekend 

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The weekly KPLU feature "Weather with Cliff Mass" airs every Friday at 9 a.m. immediately following BirdNote, and twice on Friday afternoons during All Things Considered. The feature is hosted by KPLU Environment Reporter Bellamy Pailthorp. Cliff Mass is a University of Washington Professor of Atmospheric Sciences, a renowned Seattle weather prognosticator, and a popular weather blogger. You can also subscribe to a podcast of “Weather with Cliff Mass” shows.