A dry and warm forecast will cover the region for the next week. A broad ridge of high pressure will push the storm track well to our north, occasionally allowing a few clouds to cross the region but keeping precipitation well to our north. Weekend high temperatures will be in the upper 60s, with 70 a real possibility on Monday.

The pattern stays dry through most of next week, although a few showers could fall just to our north by midweek.

Some time ago, I talked about the record for the largest snowflakes ever measured (15” wide and 8” thick in 1887 in Montana.) April Pedersen had a hard time believing it: “15 inches wide and 8 inches thick? Is this for real? Do they have 6 sides? I’ve never heard of anything like that. Is it a myth?”

I haven’t seen any pictures of the snowflakes (back in 1887 in Montana, I doubt any were taken), but I would assume that they were a collaborative effort of several snowflakes, which stuck together as they came down. Often when the snowfall is heavy and the temperature is just right (relatively warm for snow) you can get a lot of snowflakes sticking together to make very large flakes. Apparently the event was well documented.

So Steve asks as a follow-up: “I was wondering what causes the difference in size of the flakes. We get “snow pellets” here along with what a co-worker called “cotton ball flakes”, and every other size. Is it the amount of moisture falling thru the air, or the speed in which it falls, or something else?”

Actually, some or all of the above. The shape and size of a snowflake can tell you a lot about its brief history. Take the snow pellet example. Technically called “graupel”, snow pellets form when a small snowflake falls through supercooled liquid water, similar to how hail forms.

The size and shape of snowflakes is determined by a combination of the temperature profile of the atmosphere, the amount of moisture throughout that profile, and the presence or absence of vertical winds. The example of graupel (snow pellets) above usually indicates you have considerable updrafts in your snow storm… a process not unlike that which forms hail in thunderstorms. Large fluffy snowflakes can form in a moist and relatively warm snowstorm. Smaller, intricately shaped six-sided snowflakes will occur in a colder and drier airmass, which allows the crystals to form more slowly, and keeps them from joining up with others.