Snowflakes can come in many shapes, sizes

Snowflakes come in a myriad of shapes and sizes. As a child, you probably had the experience of making your own snowflake with a few snips of the scissors and white paper. Your particular design likely resembled a “dendrite,” with several arms branching out from the center. Depending on the temperature of the environment at which the snowflake forms, it can take on many shapes. In addition to dendrites, snowflakes can be shaped like columns, needles, plates or prisms, with variations in each one of those categories as well. If you can stand the cold, it’s fun to go out in the snow, catch flakes on a dark object for best contrast, and check them out with a magnifying glass.

The size of snowflakes vary greatly, but on average a snowflake (made of many snow crystals stuck together) is a bit less than a half-inch across. Light winds, and temperatures just warm enough to make the snowflakes “sticky” can result in much larger flakes. Although snowflake size is not something that is regularly recorded by weather observers, one giant snowflake was documented in a 1915 issue of Monthly Weather Review. The snowflake reportedly measured 15 inches by 8 inches and fell at Fort Keough, Mont., in January 1887. As you imagine, the bigger the snowflake, the faster it falls. The terminal velocity of a snowflake ranges from about 1.5 to 9 mph. Compare this with a typical raindrop fall speed of about 15 mph and that of a damaging 3-inch hailstone that is estimated to fall faster than 100 mph.

One of the big snow producers you often hear about in other parts of the country, though not around here, are lake effect snows. This type of scenario can produce snowfalls of 5-10 inches per hour. Lake effect snows are usually associated with the Great Lakes region, but also can occur over other lakes (or bays) in the Northeast and even over the Great Salt Lake. Lake effect snows occur when the mean temperature of the body of water is much warmer than that of the surrounding land. When cold polar air flows over a large distance of the relatively warmer water, it picks up moisture and warmth and becomes unstable (the opposite of a temperature inversion). This leads to the heavy snowfalls on the lee side of the lakes. We do not see this effect over any of the lakes in our region due to the relatively small size of the lakes and their cold water temperatures. The mountains here play a much more pivotal role “making snow” for the area by providing a lifting mechanism for the air. You need rising air with sufficient moisture to get clouds and eventually precipitation.

The winter solstice is almost here, arriving just after 4 p.m. on Friday. We’ll experience the shortest day of the year, at just under 8 1/2 hours of daylight. The coolest average temperatures will lag somewhat, occurring at the end of this month and into the first week of January. What about Christmas weather? Historically, since 1895, 78 of the Christmases have been white in the Coeur d’Alene area, meaning that there was at least some measurable snow on the ground. The snowiest Christmas was in 1951, with more than 2 feet of snow on the ground. It is still too early to tell if we’ll have snow falling on Christmas Day, but cold temperatures and snow leading into the holiday weekend may mean that the ground will already have its white covering.