What do you make of the weather we’re having so far this winter?
I expected a slow start to winter, but this has lasted much longer than even I expected. Back in November, I thought we’d see things start to shift toward a more traditional winter pattern by the third week in December, but that obviously didn’t happen. We’ve only had a few glancing blows of Arctic air through mid-January and nothing resembling a major snowstorm. The cause of our mild (so far) winter weather is an atmospheric circulation pattern called the North Atlantic Oscillation (NAO).
The NAO shifts between two primary phases, which we call positive and negative phases. When the NAO is in a positive phase, there’s a stronger than normal subtropical high-pressure area and a corresponding stronger Icelandic low-pressure area, which means that Arctic air tends to stay locked up in Canada. When the NAO is negative, both the subtropical high and Icelandic low are weaker, which allows more Arctic air intrusions into the Eastern United States.
How unusual is this season’s weather?
We don’t know exactly what causes the NAO to shift phases. El Niño and La Niña have some impact, as do other circulation patterns. In fact, we’re still trying to determine if global warming is having an effect. However, we’ve certainly had extended periods of both positive and negative NAO phases in the past, with corresponding spells of unusually mild or bitterly cold weather. People my age or older remember those particularly harsh winters of the mid-1970s, which were the result of the strongest negative NAO phases of the past 150 years.
What are the long-range predictions for the remainder of our winter here in metro Detroit and Michigan?
I think we’ll start to see a more wintry weather pattern for the rest of our traditional winter. That doesn’t mean all bitter cold and snow; it just means that we should have more days in the 20s and 30s, instead of the 40s that we got used to through mid-January. I still think we’ll get at least one or two big snowstorms. Note to school kids: There’s still hope for a snow day.
What’s the down side of all this pleasant mildness? (I’ve heard that it’s important for our lakes to freeze to prevent evaporation.)
WE NEED SNOW. I know there are some people who absolutely dread snow and — let’s face it — we all hate driving in it, but snow has many benefits.
First, Michigan gets a huge economic boost from winter tourism, including skiing and snowmobiling (not to mention the snow-removal contractors, whose livelihoods depend upon snow). Much of that revenue comes between Thanksgiving and New Year’s, and we’ve already pretty much missed out on that.
Second, spring snowmelt is what replenishes our Great Lakes water levels. So, those who love to play on the water in the summer should pray for snow, because those big storms that come up here from Texas and dump a foot of snow are just what the doctor orders for our Great Lakes.
Third, snow puts a blanket on the ground that protects our bulbs and plants from bitter cold. Think about it: If we have a day with below-zero air temperatures and there’s a foot of snow on the ground, the ground beneath is only exposed to the temperature of that layer of snow, which is not nearly as cold as the bitter cold air above it.