Mountain forecasts: The vital difference between ‘freezing level’ and ‘snow level’

The first snowflakes have already fallen in the mountains. The Washington State Department of Transportation (WSDOT) closed Cayuse and Chinook Passes — the two Mt. Rainier pass highways for the season last week. The North Cascades Highway closed for several days, but reopened again Tuesday afternoon. The next Pacific weather system moving ashore this weekend may close that highway for the season as well.

With drier weather in the forecast until this weekend, mountain forecasts will use the term “freezing level,” but this weekend, the term “snow level” will be used. The difference between these two terms that can be quite important when planning travel through the Cascade passes.

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Freezing level is used in mountain weather forecasts when there is no threat of any kind of precipitation. The forecast freezing level is for the free air freezing level. So as you climb in elevation from the warmer lowlands, you rise past the point of 32 degrees Fahrenheit – the freezing level.

Snow level is used when any kind of precipitation is forecast in the mountains. The snow level is usually around 1,000 feet lower than the freezing level. As an example at 35 degrees, it often snows at that temperature in the mountains and, at times, in the lowlands too.

During winter, the snow level can drop into the lowlands of Western Washington. For instance, during colder weather outbreaks, the snow level can drop down to at least the higher hills or even down to sea level.

Remember your chains

And for those who might be planning to travel over any of the Cascade passes, remember it is state law to always carry chains. The Washington State Patrol (WSP) reminds motorists that studded tires do not satisfy state chain requirements. If the signs are in place that chains are required, they need to be installed on top of studded tires. Studded tires became legal on Nov. 1 and must be removed by March 31.

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For those with four-wheel drive or all-wheel drive vehicles, chains still need to be installed during those significant winter storms that involve posted signs that read “chains required on all vehicles.” During “chains required” episodes, these vehicles do not need chains installed, but motorists still must carry chains – again by state law.

As always, know the weather forecast before you go, particularly when driving into the mountains so you will be better prepared and safe for whatever winter weather you encounter.

Ted Buehner is the KIRO Newsradio meteorologist. You can read more of Ted’s stories here and follow him on X, formerly known as Twitter.