Even if you are not a particular fan of winter weather, it is hard to deny that there is something about the first snow of the season.
In fact, British author J.B. Priestley expressed its transcendent nature beautifully when he wrote: “The first fall of snow is not only an event, it is a magical event. You go to bed in one kind of world and wake up in another quite different, and if this is not enchantment then where is it to be found?”
on Saturday December 12th.
On Friday night and Saturday, Dane County experienced its first substantial snow with 6.4 inches recorded at the airport. This magical event is the result of very specific physical circumstances. The sun has been down at the North Pole since Sept. 21, and the Arctic night has subsequently crept slowly southward each day since helping to produce larger and larger amounts of cold wintertime air to the north.
Several days before the first flakes fell, the atmosphere was stirring many thousands of miles away throughout the full 6-mile depth of the troposphere. Almost imperceptible at first, a weak counterclockwise spinning air mass began to develop at the tropopause — the top of the troposphere. As this feature gradually matured it was empowered to create a similar vortex near the surface of the Earth — a surface low-pressure center. As that circulation intensified, it forced the production of clouds and precipitation over a wide area, with some of the precipitation falling as rain and some as snow.
The precise track of that low-pressure center determined who got rain and who got snow. At this time of the year, if the track of a surface low is to our southeast, say on a line from St. Louis to Chicago, we here in Dane County remain on the cold air side of the storm during its lifecycle.
So the next time you enjoy a quiet walk in the snow, consider that a long list of circumstances had to have played out in precise sequence in order to deliver you the magic. It is nothing less than a miracle.
Steve Ackerman and Jonathan Martin, professors in the UW-Madison Department of Atmospheric and Oceanic Sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month.
