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The Spokesman-Review Newspaper The Spokesman-Review

Sunday, April 5, 2020  Spokane, Washington  Est. May 19, 1883
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News >  Idaho Voices

Snow may vanish even faster

Over the last week, we’ve endured heavy snow, strong winds, and finally a thaw which resulted in flooding. Finally, we’re back to some “normal” January weather – cold and gray – which I guess could be considered “better,” relatively speaking.

I was able to come up with a fact, however, that is sort of a light at the end of the tunnel. The days are actually getting longer – 18 minutes longer than back on the winter solstice Dec. 21. Not only are daylight hours increasing, but climatologically speaking, we have just passed the coldest part of the year. Average temperatures are now on the way up, albeit slowly.

Aside from the troublesome flooding, one of the nice effects of temperatures in the 40s is seeing the large piles of snow getting eaten away. One of my kids made the mistake of leaving one of our two brand new sleds out in the yard after the first big snow back in mid-December, only to have it buried days later. Who knows what other treasures we’ll find as the snow slowly disappears.

What I really wanted to point out, however, is that even if temperatures don’t spend much time above freezing, there is another factor that will cause the snow to slowly “disappear.” The term to describe this process is called sublimation. This is the process in which a solid changes into a gas, without first becoming a liquid. When liquid water changes into water vapor, we call it evaporation.

With dry enough conditions (relative humidity under 100 percent), solid water (ice/snow) can also go directly to the vapor (gaseous) phase. Snow will literally start to disappear into thin air. The opposite of sublimation is called deposition. This term refers to the process by which a gas goes directly to the solid phase without first becoming a liquid. This is one of the ways snow crystals are grown inside clouds.

Much of a snow crystal’s growth can occur when the water vapor “deposits” itself onto existing ice crystals causing them to grow and eventually fall. I can’t talk about deposition, sublimation, and evaporation, without adding one last term. Condensation, as most of you are probably aware, is the process by which a gas, such as water vapor, changes into a liquid – causing those mirrors and windows to “fog” up.

Speaking of fog, it looks like a nice ridge of high pressure is going to settle into the area for the middle of the month. While high pressure can mean sunny and hot weather during the summer, it can also lead to some cold and foggy conditions during the winter months. Milder air just above the surface leads to a temperature inversion (air getting warmer rather than cooler with an increase in elevation). The result is a stretch of days with no major storm systems … but also a stretch of days where temperatures change very little from night to day, and we are trapped under a blanket of fog.

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