The cooldown that we enjoyed over the weekend, after the prolonged warm and humid spell that began September, got us thinking about the inevitable first morning with a temperature below 32 degrees.
We are less than two weeks away from the autumnal equinox, the last day until late March on which the day is at least as long as the night.
In the last 73 years, since the official temperature for Madison has been recorded at the airport, the average date of our first 32-degree night is Oct. 1. However, the earliest such night occurred on Sept. 11, 1955 – after a summer in which a record 40 days with a high temperature of 90 were recorded. This early freeze was nearly equaled by 1962 and 1963, when it occurred on Sept. 12.
More recently, the only fairly early date for the first freeze was Sept. 16, 2007. The latest such night also occurred in the 1950s – Oct. 17, 1959 – with a more recent competitor landing on Oct. 14, 2005.
Interestingly, for a period of 23 years (1940-1963) we have simultaneous records from the official recording site that used to be located in Downtown Madison. The average first freeze at that location is much later, around Oct. 20. The earliest and latest dates at that site are also quite different.
So, though on average the first freeze occurs about 10 days after the equinox at the airport, your own home may record a substantially different first freeze date.