It's snow time!

It's that time of year when we have to watch out for winter precipitation. In our region, that 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 to form flakes that drop to the earth. If the atmosphere is uniformly cold, these frozen flakes land as snow.

It's that time of year when "snow" becomes a favorite topic

(Photo by Metro Creative Graphics)

When it's very cold and the atmosphere is relatively dry, the snow has a light, powdery texture. When it's warmer and we have 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; for example, when snow forms with red colored algae around large water bodies producing "watermelon snow." This snow is pink and smells like watermelon.

The lightest snow fall is a flurry. A locally heavy snow, often times arriving in a narrow band, is a squall. A heavy, uniform snow event is called a blizzard.

The heaviest snow accumulation ever recorded in the U.S. occurred from Feb. 13 to 19, 1959, in Mount Shasta, Calif., when 15 feet, 8 inches of snow fell.

Sometimes snow forms in the upper atmosphere, hits 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, the snow will melt and cool enough that it freezes when it hits the surface as freezing rain. Of all the winter precipitation events, the freezing rain usually causes the most damage.

Winter food source for birds

There are a number of native birds that tough it out with us during the winter and do not travel to warmer climates. These year-round residents often adapt their eating habits to the season, going from a diet that includes insects when it's warm to more vegetarian fare of seeds, leaf buds, berries, nuts and other plant parts during the winter.

Some enterprising birds will root around on the ground in search of hibernating insects, but most depend on food from plants or offerings from sympathetic homeowners. Winter can be a very stressful and dangerous time for these birds since food is scarce, it's cold and windy outside, and deciduous trees have lost their leaves so they are more exposed to predators.

Many people help our winter residents by putting out bird feeders with seed and suet along with a water source. In addition to these measures, you can help birds by planting an assortment of trees and shrubs that provide winter cover and or a food source for many species. Some plants that provide favorable cover and food for birds during the winter include gray and silky dogwood, hawthorn, crabapple, black gum, hollies (especially American and winterberry holly), chokeberry, bayberry, hackberry and sumac. Evergreen trees and shrubs provide a safe haven that birds can utilize to avoid predators or escape the winter chill. Many of these trees have cones with nutritious seed or berries that are also valued by birds. The eastern red cedar is a good example of such a tree. This native cedar is a slow-growing, dense conifer that produces a red berry that is a prized food by many over-wintering birds, especially cedar waxwings.

Nature Notes for 12/19/2010