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The Spokesman-Review Newspaper
Spokane, Washington  Est. May 19, 1883

New year offers a frosty reception

Michelle Boss

January has been an interesting month. After picking up nearly a foot and a half of snow or more in Spokane and Coeur d’Alene during the first week of the month, we’ve been experiencing quite a dry spell. We’re having to round the snow amounts to the nearest half inch, rather than the nearest foot these past few days. Temperatures have shown similar swings. After a dip into the deep freeze at the beginning of the month, where temps fell below zero, a winter high-pressure pattern of low clouds and fog kept a lid on afternoon temperatures, but also held up overnight lows for much of the remainder of the month. Overall, the average monthly temperature ended up only about a degree cooler than normal.

While snow was a big problem in our neck of the woods at the start of the month, it was ice that capped off the end of the month for folks in the Midwest, resulting in fatalities on area roadways as well as widespread power outages. The most severe icing (as much as two inches accumulation) occurred in parts of northwest Arkansas and east central Oklahoma. The stage was set when a stationary front set up east to west across Oklahoma and Arkansas. Cold air was firmly entrenched north of the front, while warm moist air was surging northward south of the front. Heavy precipitation fell in this region, where from south to north, precipitation went from rain, to freezing rain, sleet and then snow. The freezing rain occurred in a narrow band where subfreezing air at the surface was very shallow, allowing the precipitation to fall as rain, then freeze as it hit the chilly surfaces on and close to the ground.

Locally, on a smaller scale, freezing drizzle resulted in slick roads which caused a multi-vehicle accident in Post Falls last Tuesday. Though temperatures in the area never climbed above freezing, liquid precipitation was falling due to the presence of supercooled water droplets in the clouds. Though it is true that ice begins to melt at 32 degrees F. (0 degrees C.), water does not necessarily freeze at temps below that. In fact, pure water can be cooled to as much as -40 degrees F. and still remain in its liquid form. Liquid water below 32 degrees F. is called “supercooled” water and can remain a liquid if the size of the droplet is small enough and it is left undisturbed. Any contact with a solid object (such as roads) would cause the water to immediately freeze.

Icing of a different kind affected areas in Lincoln County just west of Spokane during the middle of the month when hoarfrost, freezing drizzle, and freezing fog built up in such high amounts that power lines and tree limbs were weighed down and damaged. Unlike freezing drizzle and freezing fog, hoarfrost occurs when water vapor is directly deposited (sublimates) onto a surface which is below freezing. The pattern this type of frost makes on various objects outside can be quite stunning.

Michelle can be reached at weatherboss@comcast.net