Dear Tom,
What is the date for the latest first frost in this region? Are we close to setting any records this year?
—Sarah Gruber, Essex
Dear Sara,
We are not. The common yardstick for marking the end of the growing season, it the first day the mercury drops to 32 degrees or lower. The city’s long-term average (since 1871) is Oct. 24. When considering the period since 1942, the time when the official thermo- meter was moved to an inland location away from the lakefront, the average date is Oct. 20. Chicago weather historian, Frank Wachowski, checked the records and found the all-time latest occurrence of the first official freeze was Nov. 24, 1931. Since 1942, the latest date has been Nov. 13 in 1946, and again in 1975. In 2016, the first freeze occurred one day earlier, on Nov. 12.