Some winter storm warnings are better than others

Over the last week, the region was hit with two storm systems. Last Saturday’s storm was a bust over Spokane/Coeur d’Alene in regards to snow, though the winds and cold temperatures did descend upon us with a fury. The second storm came with much less wind, but blanketed a large area with record-breaking 24-hour snow amounts. Both times we were under a “winter storm warning.” What then, made the outcomes so different?

Ahead of the first storm, we had some relatively mild air in place with above freezing temperatures. While snow can easily fall even with temps in the middle or even upper 30s, it makes sense that such warm temperatures really keep a lid on any accumulations. During that particular storm, the computer models put the Spokane/Cd’A area right at the border line of rain and snow. Forecasting accumulations then becomes a challenge, because a couple of degrees up or down can make the difference between a heavy, wet 4-6 inches of snow, or a puddle of nearly nothing. Meteorologists use what’s called a “snow to liquid ratio” to calculate how much snow can be produced by a certain amount of water. When temperatures are near freezing, the snow to liquid ratio may be 10 to 1 or less. In other words, .1 inches of water would make 1 inch of snow or less. This storm dropped about .3 inches of water over 2 days, amounting to 3 inches or less of snow locally. It was just a little too warm, and some locations saw a few hours of plain old rain. What snow did fall once the cold air started filtering in, blew around so much that coverage was spotty. Higher elevations did pick up 6-plus inches, along with a few spots which got caught under localized heavy snow bursts. Again, it became more of a wind and subsequent cold event for Spokane/Coeur d’Alene.

Fast forward four days to storm number two. Lack of cold air would not be an issue. Deep cold air was already in place across the entire Northwest, so much so that Portland and Seattle would both see enough wintry weather to wreak some havoc in those cities. A slow-moving low-pressure system was coming in from the northwest, bringing cool and moist Pacific air right to our region, and setting up a conveyor belt of heavy snows which blanketed nearly all of Eastern Washington and North Idaho. Due to the much colder temperatures, the snow to liquid ratio was much higher, around 30 to 1. In other words, just .1 inches of water would produce 3 inches of powdery, fluffy snow.

I do not have the final storm tallies as I am writing this article, but snow reports of 1-2 feet will likely break many daily snow records. The previous 24-hour snowfall record for Spokane was 12.7 inches set back on January 21, 1954. I believe Coeur d’Alene’s previous record was around 14 inches for a 24-hour period.