Weathercatch: Be wary of dreary ‘wintry mix’

If you live in the Inland Northwest, you probably know that “wintry mix” is not a type of winter party snack. Instead, it’s an informal meteorological term used to describe when varied forms of precipitation occur in some combination or in succession: snow, rain, freezing rain and sleet.

Recently, we’ve had a lot of straight rain. But as temperatures begin to cool off next week, doses of wintry mix will become more likely. A far cry from the pristine white sparkle of holiday cards, it can make the outside world slushy, icy and just plain messy. It can also be hazardous, whether walking the dog, driving to the store or flying on a plane.

Whether precipitation remains snow or turns into rain, freezing rain or sleet depends on temperature variations that snowflakes encounter as they fall through layers of the atmosphere to the ground. Whereas subfreezing air layers form snow and ice, layers with temperatures above 32 degrees initiate rain.

And boy, our region has seen plenty of rain the second half of this month. Not only has the air been warmer at ground level, but also in the atmospheric layers. The outcome? As snow descended from clouds and fell through above-freezing air layers, it melted into rain.

Had there been enough temperature differences in those layers – some with cold air and others with warmer air – the atmosphere could have unleashed a wintry mix. We might have experienced snow mixed with rain or sleet. Or, we could have gotten one after another.

Of the multiple precipitation forms that can turn up in a wintry mix, freezing rain is the most dangerous. It starts as snow, melts into rain and falls as liquid until the raindrops make contact with a surface that’s below 32 degrees. This causes the rain to freeze, resulting in a coating of ice that makes roads, sidewalks and runways extremely slick. It can also weigh down tree branches and power lines, making them break. Freezing rain is especially risky when hidden by a layer of snow that falls afterward.

What about sleet? Like freezing rain, its journey begins when snow melts into rain as it falls through a wedge of above-freezing air. But sometimes the rain refreezes as it passes through a layer of cold air, creating sleet. Small, opaque ice pellets can be seen bouncing off pavement, cars and other hard surfaces.

If you’re wondering where hail fits into this wintry mix scenario, it doesn’t. Though hail is similar to sleet, it rarely occurs during winter, instead forming in the bottoms of clouds during thunderstorms. And rather than falling as small, clear ice pellets, hailstones arrive as irregular-shaped lumps of milky-colored ice – sometimes big as golf balls or larger.

Wintry mix is a more common occurrence in the Inland Northwest than in Fairbanks, Alaska. After all, the atmosphere in this region is more likely to have those warmer wedges of air that alter snowflakes as they tumble toward earth. On the flip side, we’ve had so much warm air recently that all we’ve gotten is rain. Again, this could soon change. Temperatures are expected to begin dropping a day or two after the ground hog emerges from his burrow in Pennsylvania on Feb. 2.

And if the weather conditions are right, Punxsutawney Phil won’t see his shadow – or slip on freezing rain.