Only limited areas of the Upper Midwest have reported a hard freeze, defined as a temperature of 28 degrees or less, as of this morning.
Areas shaded in green (below) show where the first occurrence of 28 degrees has occurred. The area circled in red usually has had a hard freeze by this time of the year.
This map shows the progression of fall color changes as of this date.
However, a series of cold fronts will be passing across the nation this week and next. Each will usher in colder air and likely freezing temperatures.
It’s shaping up for a cold Halloween. A sagging jet stream will allow unusually-cold temperatures to overspread a large part of the nation.
An unusually-strong push of cold air will result in widespread freezing temperatures next week.
Low-Temperature Outlook Oct 30th