Midwest Cold Weather: Illinois-Indiana Could See First Frost Arrive Soon

Quincy, IL – Illinois residents in the St. Louis region may want to start thinking about protecting sensitive plants as the calendar approaches the period when the area's first frost and freeze typically occur.

According to the National Weather Service in St. Louis, frost is unlikely across the region over the next week. However, forecasters said Sunday that the area is reaching the time of fall when the first frost and freeze are commonly recorded.

Historical averages vary considerably by location. In Quincy, the average first frost, defined as temperatures below 36 degrees, is Oct. 11. The average first freeze below 32 degrees is Oct. 20, while the average first hard freeze of 28 degrees or colder arrives Oct. 31.

Farther south, Cahokia Heights typically experiences its first frost around Oct. 12 and first freeze around Oct. 21. Hillsboro's averages are Oct. 12 for the first frost and Oct. 18 for the first freeze.

Salem typically reaches its first frost around Oct. 14 and first freeze around Oct. 25, according to NWS climatology.

Those dates are averages, not forecasts. Historical records show frost can occur substantially earlier or later in any particular year. Quincy, for example, has recorded its first frost as early as Sept. 12 and as late as Nov. 7 within the climatological data shown by the weather service.

The NWS figures are based on 1991-2020 climatological data. Gardeners and homeowners should continue monitoring upcoming forecasts rather than relying on historical averages to determine when plants need protection.

For now, the immediate message is reassuring: The weather service says frost is unlikely during the coming week.