Everything You Need to Know about the Winter Solstice
By Justin Poublon
December 20, 2018 - 2:30 PM CST | 177 0
The 2018 winter solstice will occur tomorrow, Friday December 21st. The winter solstice is the shortest day of the year with only 8hr 53min of daylight in Wisconsin. It's the point where the earths axis tilts the northern hemisphere the furthest away from the sun.
If it's the shortest day and we're the farthest away from the sun, why isn't the winter solstice also the coldest day of the year? Good question.
The northern hemisphere experiences what I call the lag effect. It's why equinox and solstice dates are nice to know but practically irrelevant to Wisconsin Weather. The weather on these dates can be totally opposite from what you would expect. If you want to know what season it is, start by walking outside.
The Lag Effect
When you boil water on the stove; the water doesn't go straight to room temperature when you turn off the heat, right? It takes time to cool. The sun changes far more gradually. It's basically been on simmer the last two months and now we are finally...off.
During the winter solstice; cold, snow, and ice is not just accumulating to the north; it's accelerating. In winter the sun has a shallow angle with earth surface. This means snow, ice, and clouds will reflect even more energy back out. It's what I call a positive feedback loop. Cold is multiplying. It requires increasing sun energy in January and February to interrupt the loop, start the changing process, and maintain global balance.
Unleashing the Polar Vortex
Arctic air begins to flow south in December, January, and February and continues into early spring. Due to gravity/density, the cold air would love to flow south to the equator if it could. The jet stream current is the boundary between cold in the north and warmth to the south. It dictates our weather pattern. It decides where arctic air can spill out and where it remains locked away. As the days become longer in January and February, warm air driven above the arctic dome known as stratospheric warming events cause the polar vortex to become unstable. The jet stream buckles and unleashes the "polar vortex".
Wisconsin Winter Temperature Trends
The coldest day of the year in Wisconsin tends to occur around three weeks later in January. January and early February is the coldest with average low temperatures in the single digits or teens.
Interesting note: Ice ages are associated with decreased solar energy reaching the earth due to 26,000 year long orbital cycles known as Milankovitch cycles. There are shorter cycles as well.