'Killing Frost' Could Happen Any Time Now

‘Killing Frost’ Could Happen Any Time Now

The first frost in Kane County — known as the “killing frost” — should happen very soon.

According to data supplied by the National Weather Service Chicago, we usually get the first autumn frost sometime between Oct. 11 and Oct. 20.

So far, we’ve dodged that bullet.

But even though temperatures in Kane County communities were at or close to 70 degrees in the past 24 hours, the lows already are dipping into the 30s.

During the past 24 hours, as of Wednesday (Oct. 18, 2017) morning, Aurora reached 70 degrees for a high temperature but recorded a low of 45 degrees. Elgin got up to 70, as well, but recorded a low of 39 degrees.

As you can see by the NWS graphic below, the earliest first autumn freeze in Chicago was Sept. 22, 1995. The latest freeze was Nov. 24, recorded in 1931.

Last year, we had a Freeze Watch on Oct. 16.

This Autumn’s Temperatures

As you can see by the map above, the first frost already has happened for a lot of communities in Wisconsin, Minnesota, Michigan and Iowa. There were even two in Missouri, south of Illinois.

How Do You Determine Frost?

Although 32 degrees is used to identify frost, visible frost can be seen on the ground and objects when the reported temperatures are slightly above 32 degree, the NWS says.

On calm, clear nights, the cold, dense air collects near the ground. Under these conditions, the temperature near the ground can be a few degrees cooler than at the 5-foot height of the official National Weather Service temperature sensors.

The actual date varies from year to year. For tender plants, add two weeks to the average date in the spring to protect against the possibility of late season frost. In the fall, subtract two weeks from the average date to be on guard against an early frost.

Open, grassy areas are usually the first to experience frost, while areas under trees are more protected. Homeowners can protect plants by covering them when a frost is expected. Plants near heated buildings sometimes are spared too. Because of the abundance of warm buildings and trees, we see frost arrive in town a little later than in the countryside.

Check with University of Illinois Extension for suggestions on dealing with frost.

Why Should I Care?

The big impact is that sensitive vegetation can be damaged or killed by that first frost.

Of course, that includes agricultural concerns as well as residential gardens.

With fall frosts, precautions and management strategies may need to be taken, for example, with the harvesting and feeding of the sorghum family of annual grasses.

If you are only expecting a light freeze, you may be able to protect plants in a freeze simply by covering them with a sheet or a blanket. This acts like insulation, keeping warm air from the ground around the plant. The warmth may be enough to keep a plant from freezing during a short cold snap.

For added protection when you protect plants in a freeze, you can place plastic over the sheets or blankets to help keep warmth in. Never cover a plant with just plastic, however, as the plastic will damage the plant. Make sure that a cloth barrier is between the plastic and the plant.”

For information on how to protect plants from a freeze, visit this link on the Gardening KnowHow website.

SOURCE: National Weather Service Chicago