Frosty Nights; Why No Freeze Warnings?

For the third time this fall, a Frost Advisory is in effect for the entire Stateline. That means the formation of frost is likely in most backyards tonight into early Friday morning. Temperatures are expected to remain just above the freezing mark in many spots, but a few locations in Jo Daviess, Carroll, Stephenson, Green, and Rock Counties could see temperatures in the 30-32° range. Technically that is considered freezing, but the National Weather Service is not issuing Freeze Warnings. Instead, they are sticking with Frost Advisories. Why is that?

The NWS won't issue Freeze Warnings unless a widespread freeze event is expected across a particular county. In other words, unless the NWS is confident that a majority of any given county will experience temperatures below 32°, they won't issue a Freeze Warning. For tonight, some parts of Jo Daviess, Carroll, Stephenson, Green, and Rock Counties will likely dip to 32°, if not lower. However, each of those counties will likely have many locations that stay at 33° or above tonight. Thus, a Frost Advisory in effect despite some locations likely seeing a freeze event tonight.

If a widespread freeze event is anticipated, a Freeze Warning will be issued. Thus far this fall, temperatures have not met the guidelines for a Freeze Watch/Warning. It doesn't look likely that we will meet Freeze Warning credentials for the next week or so, per the latest forecast models. Once temperatures are forecast to drop to 32° or lower for most of any given county, a Freeze Warning will be issued. And, once the first "widespread" freeze event occurs in a given area, the growing season officially comes to an end. As a result, Frost Advisories and Freeze Watches/Warnings will no longer be issued. Frost Advisories and Freeze Watches/Warnings are only used in the fall until a killing freeze event occurs. They are used in the spring when it is late enough to cause damage to new crops and plants.