Sub-Zero Recipe


Start with 24 hour nights, season with snow, and watch the temperature tumble. That's the recipe for bitterly cold weather. The nights are long in an Arctic winter. Above the Arctic Circle on the Winter Solstice the Sun does not rise. The farther north toward the North Pole the more days the Sun spends below the horizon. Add snow cover and there is no way what sunlight there is will warm the earth - at least not until the daylight lasts longer. 

In polar regions the very low sun angle of winter combined with snow on the ground causes most of the sunlight to be reflected back to space instead of being soaked up by the earth in the form of heat. At night the snow cover radiates heat to space - and temperature get colder. The only thing that changes this scenario is the advection (movement) of warmer air from the south (or from the north in the Antarctic) into polar regions. That is, in the Arctic southerly winds bring warmer air from the south to the north. That warms the temperature temporarily. In fact, bringing warmer air into the Arctic is part of the process of balancing global temperatures. The warmer air is cooled as it moves  north and mixes with colder air. 

The map above shows the next surge of Arctic air moving into the Upper Midwest. Night time temperatures over the weekend will be colder than 15 to 25 below zero in northern areas - and very cold further south as the cold air heads south. It will be modified as the air moves into areas in the southern Midwest, and points south, that are not as cold. By looking at the station model plots is it possible to see the wind directions at each reporting station. There is a huge area of northwest winds spreading out of Canada.