Strange winter phenomenon

Snow across the Inland Northwest has not been plentiful this season, despite the formation of a new La Niña in the waters of the south-central Pacific Ocean. As I mentioned last week, the heaviest snowfalls of this winter have been east of our region. Florida experienced some of the coldest weather in decades over the weekend. Below-freezing temperatures broke pipes at Walt Disney World as wind chill temperatures were near 10 degrees. The long-range computer models are indicating more cold weather to move into the eastern part of the country this weekend.

The big storm last month made international headlines as over 1 million people went without power. Blizzard conditions swept over the AFC championship game in Denver as the football field got completely covered with snow in the second half of the game after starting snow-free.

Here in the Inland Northwest, January was a drier-than-normal month as nearly 1.70 inches of moisture was measured at Cliff Harris’s station. The January normal is 3.77 inches. At the Spokane International Airport, close to 1.2 inches of rain and melted snow were reported last month, compared to a normal of about 2 inches.

The strong high-pressure ridge is expected to hold on across the western U.S. into at least the first 10 days of February. Football fans know that the upcoming Super Bowl will be played in Santa Clara, Calif., on Feb. 8. As of this weekend, skies are expected to be partly cloudy with the possibility of a few showers.

Toward the middle of next week, there are indications that colder air may filter down from Canada and bring some snow to our region. There is a chance of more snow in the lower elevations toward the middle of the month.

The big storm in the U.S. last month did bring up a strange winter phenomenon called “exploding trees.” In this case, trees don’t actually explode with fire or debris. Instead, they can split suddenly and violently when extreme cold causes rapid internal stress. A tree’s first line of defense against freezing is its bark, which usually provides efficient insulation against cold weather. During sudden temperature drops, moisture inside tree trunks freezes and rapidly expands. The internal pressure can cause the wood to split violently, producing a loud crack, similar to the sound of fireworks or thunder, that echoes through frozen forests. These events are most common during Arctic air outbreaks across Canada, the northern United States, Scandinavia and Siberia.

Another winter phenomenon that creates a loud boom is frost quakes. Also known as cryoseisms, frost quakes are one of the most surprising and unsettling events in cold regions of the Northern Hemisphere. Unlike earthquakes, they are not caused by shifting tectonic plates. Instead, they occur when rapidly dropping temperatures cause water in the soil or bedrock to freeze and expand.

For a frost quake to occur, the ground must first be saturated with moisture from rain, melting snow, or a winter thaw. When an intense cold front arrives and temperatures plunge quickly, this trapped water freezes almost instantly. Because ice expands as it forms, enormous pressure builds within the frozen ground. With no ability to flex, the soil or rock fractures suddenly, releasing energy as a loud boom and brief ground shaking.

People often describe frost quakes as sounding like explosions or thunder coming from underground. They typically occur at night or in the early morning, when cooling is most rapid and can rattle windows or crack pavement. Like exploding trees, frost quakes are most common in places such as Canada, the northern United States, Scandinavia and Siberia. However, there were reports of frost quakes in the southern U.S. last week from the big storm.

One very rare winter phenomenon that has been seen in Idaho is snow rollers. They are one of the rarest and most visually striking, as they appear as cylindrical or hollow, doughnut-shaped snow formations scattered across open landscapes, looking as though someone carefully rolled hundreds of snowballs by hand. Some have referred to them as “nature’s tumbleweeds,” as snow rollers are created entirely by wind under very specific weather conditions.

For snow rollers to form, a hard base layer of snow or ice must already cover the ground. On top of this, a fresh layer of loose, slightly sticky snow is needed — cold enough to hold together, but not so cold that it crumbles. When strong, steady winds blow across open terrain, they catch small clumps of snow and begin rolling them along the surface. As the snow rolls, it collects additional layers, growing larger with each rotation. Many snow rollers become hollow as inner layers collapse or are blown away.

Snow rollers are most commonly observed in the Northern Hemisphere, particularly across the Great Plains, Midwest, Canada and parts of northern Europe. They are usually short-lived, often collapsing or melting within hours as temperatures or wind conditions change.

There have been several occasions when snow rollers have been spotted in Idaho. Back in 2019, an observer in Worley stumbled across an area of snow rollers and provided photographic evidence. There was another instance of this phenomenon back in 2016 near the Silver Creek Preserve in south-central Idaho.

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Contact Randy Mann at [email protected].