Northland Nature: February brings rime, rope
The second half of January was quite different from the first half and gave us some winter weather to remember. Most was in the form of cold. When the early weeks of the month were about 10 degrees above usual, the latter dropped to nearly 15 below normal.
We got plenty of impressive cold, with many in the Northland seeing 40 degrees below zero, but it was not so snowy. Most of the 11 inches recorded at the weather service did fell in the second half, but this number is still far below what is expected for January.
And then we stepped into February.
This shortened winter month is typically a time of dry conditions — not a lot of snow — and though it can be very cold, usually not as much as January. Probably the most notable phenomenon of this month is the lengthening days.
We began the month with about nine and a half hours of daylight and now as we near the end, we see 11 hours.
The first half held another surprise. This month with normally the least amount of snowfall of any winter month has become the most. At the National Weather Service in Duluth, 28.5 inches of snow were measured in the first two weeks of this month — more than four times the usual and more than twice what fell in January. Most fell in cold enough temperatures to be a dry powder.
But there were some interesting snow and other precipitation happenings.
Early in the month, the night of Feb. 2-3, we experienced a fog. With a temperature in the 20s and calm winds, the supercooled droplets settled onto tree branches. The following day, we woke to the nearby forest coated in a frost called rime.
Rime can form in different shapes, but when I went out to take a closer look, I noticed the trees were coated with numerous needle-like spikes, some up to a half-inch long. This fascinating forest scene remained for a couple of days, but subsequent winds and snows brought most down. I was a bit surprised to find a protected woods a week later where the rime was still clinging to the branches.
A few days later, we received several inches of snow. It settled on the trees, but conditions after the snow brought down much, but not all, of this cover. Temperatures rose a bit and in another protected site, I found a different winter weather phenomenon: snow rope.
Also called snow garland or "snow snakes," snow rope is an interesting happening seen on the horizontal branches of trees. Though not common, it is a regular Northland winter phenomenon.
Snow that falls as flakes quickly changes when landing on a substrate. This buildup of snow forms a snowpack. Whether on the ground or on trees branches, the snow within goes through changes called metamorphosis.
Flakes are transformed into rough spherical grains or granules. They get pushed together and tend to coalesce, forming a bond. This bonded snow stays lying on the branch until additional snow and temperature changes cause it to begin to sag; also response to gravity.
Eventually, some of these bonded snowpacks will hang as single units from the branch, making a shape like garland of Christmas: snow rope. Most likely, when the temperatures are in the 20s and not too windy is the time to see this.
Snow rope is a great sight on winter trees, but it is fragile. If you see this, best to photograph it soon. February has given us rime and rope; what else is in store?