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Snow can fall in above-freezing temps

I recently drove through the Diamond Lake area. It was snowing but not sticking to the ground. I know it was above freezing. How was it still snowing?

— Joann H., Jacksonville

Well, Joann, it sounds as if you experienced the anomalies of Oregon weather firsthand. Almost all precipitation begins as snow, but the warmest temperature at which snow can fall varies and depends on different factors.

As long as the air temperature is below freezing on the way to the ground, the precipitation will remain as snow. 

Sometimes, a layer of sub-freezing air reaches near the ground, but not all the way down. Even if the temperature at ground level is above freezing, the snow may not have time to melt in the distance from the freezing air to the ground. So it's possible for this shallow warm layer to be 2 to 4 degrees warmer than the freezing temperature a short distance above. The snow melts on contact with the warmer ground, or quickly after reaching it. But even in the case of wet, melting snowflakes, the temperature at the ground is usually no warmer than a few degrees above freezing.

This is why sometimes you see snow falling, but little or no snow accumulation on the ground. The precipitation is traveling through several temperatures before it reaches ground level.

Send questions to “Since You Asked,” Mail Tribune Newsroom, P.O. Box 1108, Medford, OR 97501; by fax to 541-776-4376; or by email to youasked@mailtribune.com. To see a collection of columns, go to mailtribune.com/youasked. We’re sorry, but the volume of questions received prevents us from answering all of them.