It’s that time of year again when we have to watch out for winter precipitation. In our region, that precipitation can take the form of snow, sleet, or freezing rain. The kind and amount of precipitation we get depends on three factors: the temperature, the amount of moisture in the air, and the wind. Snow forms when water vapor freezes in the upper atmosphere into ice crystals. These ice crystals bind together with dust particles or other small objects forming flakes and drop to the earth. If the atmosphere is uniformly cold, then these frozen flakes land on the earth as snow and when it’s very cold and the atmosphere is relatively dry, the snow has a light, powdery texture. When it’s warmer with a lot of moisture in the air, the snow is more granular and we have a heavier, wet snow.

There are all sorts of names for the type of snow falling; an interesting condition happens when snow forms with red colored algae around large water bodies producing watermelon snow. This snow has a pink color and it smells like watermelon. The lightest snow fall is referred to as a flurry. A locally heavy snow, often times arriving in a narrow band, is referred to as a squall. A heavy, uniform snow event is called a blizzard. The heaviest snow accumulation ever recorded in the US occurred from February 13 -19, 1959 in Mount Shasta, California when 15 feet 8 inches of snow fell. Watermellon snow (Courtesy photo)

Sometimes snow forms in the upper atmosphere, meets a warm pocket of air and melts, then encounters another cold pocket before it hits the ground. If that warm pocket is fairly narrow, the snow melts then refreezes into a pellet shaped ice crystal known as sleet. If the warm section of the atmosphere is fairly large, then the snow will melt and cool enough that it freezes when it hits the surface as freezing rain. Of all the winter precipitation events, freezing rain is usually causes the most damage.

Nature Notes for 12/27/2015