A Freeze Warning is in effect Friday morning for much of Northern Illinois and Northwest Indiana. A few other communities are under a Frost Advisory for slightly warmer temperatures, while the City of Chicago is exempt from both cold weather headlines as the urban heat island effect keeps temperatures higher.

A Freeze Warning is issued for the first widespread freeze of the season, marking the end of the main growing season. Those with sensitive outdoor vegetation are advised to take steps to protect plants, and do the same for unprotected outdoor plumbing. Once the first widespread freeze of the season has occurred, the National Weather Service's freeze program is discontinued for the rest of the season as to avoid Freeze Warnings every time the temperature dips through the winter.

Similarly, a Frost Advisory marks the first widespread frost of the season. Frost typically occurs when overnight temperatures dip to between 33-37 degrees. Frost in both spring and fall seasons can be a concern to farmers, landscapers, and gardeners. 

This first widespread freeze of the season comes slightly later than what we have typically experienced over the last 30 years. Rural areas south and west of Chicago, along with much of northwest Indiana, typically see their first freeze between Oct. 11-20, according to the National Weather Service. Areas closer to the lakeshore that will not see a freeze Friday morning typically see their first freeze Oct. 21-30, while portions of the Chicago lakefront can take until Oct. 27- Nov. 5.

Officially, the first freeze at Chicago O'Hare is typically recorded Oct. 23, so this year will be another late first freeze. Last autumn, Chicago O'Hare recorded its first freeze on Nov. 20. As the climate warms, the first freeze is arriving nearly two weeks later than it used to in Chicago. The average first freeze between 1961-1990 came Oct. 11.

Chicago O'Hare's earliest first freeze was recorded Sep. 22, 1995 when temperatures dropped to 32 degrees. Chicago's latest first freeze on record occurred Nov. 24, 1931, when temperatures dipped to 30 degrees.