How many times in a winter season should we expect temperatures as cold as -20 degrees? Not as many as in the past. During the terribly cold 1880s, the average number of -20 degree nights was around 20 per year. The record is 39 during the winter of 1886-87. By the early 1900s, the average had dropped to around nine per year, where it remained until our climate began to warm in the 1980s. By the 1990s, the average had dropped to around five per year, and the running average is presently around four.
Last winter, which was a particularly cold winter by modern standards, there were eight nights below -20 degrees (and one very cold afternoon). So far this winter, there have been just two nights as low as -20 degrees. Since records began, there have been ten winters without any -20 degree readings. Eight of those winters have occurred since 1980.