There is no doubt that this winter’s prolonged and sometimes desperate cold has been unusual.
Interestingly, for all the talk of the “polar vortex” and our unusually prolonged cold in central North America, it has been a remarkably “warm” winter when considered from the hemispheric perspective. Unusually warm weather in the West has offset the frigid winter across the East and much of the Midwest.
But closer to home, scientists at the National Weather Service Forecast Office in Milwaukee just reported that this year’s start to winter (defined as the period from Dec. 1 to Feb. 11) is the 10th-coldest of all time and the coldest in 35 years. To this point in the winter, our average daily temperature has been just 13 degrees Fahrenheit.
Four times each day we calculate the areal extent of air colder than minus 5 degrees Celsius ( 23 degrees Fahrenheit) at 1 mile above the surface using weather data analyses (not forecasts) supplied by the National Center for Environmental Prediction. Averaging the four measurements per day together creates a daily value of the areal extent of this cold pool.
In the accompanying chart, this daily value is plotted (thick line) against the 64-year average (dashed line) for each calendar day from Dec. 1 to Feb. 11. Thus far, this season is one of the most below-average years in the 64-year record.
Some have suggested that this winter’s cold proves that global warming is a hoax. Conversely, it has provided clear evidence that regional weather drives local cold snaps while climate lurks in the background — testifying even in the face of our cold that the hemisphere is unusually warm.