Temperatures 15 to 18 degrees colder than normal.
Northern Illinois, northern Iowa, northern Nebraska, the Dakotas, Minnesota and Wisconsin could possibly see frost between September 6 and 10,
On the morning of Sept. 7, lows could fall between 34 and 39 degrees Fahrenheit—between 15 and 18 degrees colder than normal, says Clark. That would be a “legitimate threat” of an exceedingly early frost.
Thanks to Mom2kids for this link