Frosty Facts for the Twin Cities

As of Nov. 6, there hasn't been a 32 degree temperature or colder at the Twin Cities International Airport yet this season. Looking at the past weather records from 1871-2015 a 32 degree temperature has occurred about 90 percent of the time by Oct. 28 or about about 9 out of 10 years. The first 32 degree temperature has occurred in November seven times. The last time a first freeze went into Nov. was 1958, when the first 32 degrees or colder was Nov. 6, according to a news release from the Department of Natural Resources.

Frost statistics can be difficult to compare due to the fact that for a good part of the Twin City observing history, the official thermometer was on top of a building in downtown Minneapolis, or on top of the old Wold Chamberlain building at the airport. The heights ranged from 105 feet above the ground in downtown Minneapolis, to 32 feet above the ground at the International Airport. This would in effect cause the official temperature to miss some of the calm clear nights when cooler air would settle closer to the ground. From 1891 to 1959 when the thermometer was on top of a building, there are three times when the first frost date was in November, with the latest on Nov. 7, 1900.

Beginning with Jan. 1, 1960 the thermometers were moved to a location approximately five feet above the ground at the airport, and they have remained at this height ever since. The latest frost during this era is Oct. 30, 1973 with the earliest frost occurring a year later on Sept. 3, 1974. The median (1960-2015) frost date is October 6.

One more factor must be mentioned when discussing frost. Over time the urban heat island of the Twin Cities expanded outward from the center of the downtown areas, as more of the surrounding landscape turned from fields to blacktop. This may also have an effect on the first date of frost over time as well.

Image via Alan Turkus, Flickr, Creative Commons