I love the weather in Illinois – hardly ever a dull moment. This October we experienced days in the 90s, the first fall frost, the first snow of the season, and widespread heavy rains.
The statewide average temperature departure for the first 9 days of October was 11.5 degrees above normal. There were many reports of temperatures in the 90s during this period, including a high of 94 degrees in Fairfield on October 7.
After the passage of a strong cold front, temperatures dropped and remained much cooler for the rest of the month. The temperature departure from October 10-31 was 5.7 degrees below normal. The warm and cold periods balanced out, leaving the statewide average temperature for October at 54.0 degrees, 0.4 degrees below normal.
Freezing temperatures arrived across most of Illinois on October 21st. The lowest reported reading was 19 degrees at locations near Stockton, Shabbona, and Champaign. Historically, the average dates for the first fall frost are in October across the state.
The first snow of the season fell on October 12th. I happened to be driving through it between Kankakee and Champaign (photo below). There were widespread reports of traces of snow, meaning it melted as it fell. A few areas reported a small amount of accumulation, including Moline and Bloomington with 0.2 inches. We do not always see snowfall in October in Illinois, but it does show up in the records from time to time. However, it is not a reliable indicator of the upcoming winter.
Precipitation was widespread across Illinois in October. The statewide average was 3.81 inches, 0.57 inches above normal. Amounts of 4 to 7 inches or more were common in the northern half of the state, which is well above normal. Meanwhile, most of the southern half of the state was drier with amounts in the 2 to 4-inch range, which is much closer to normal for October. The largest monthly total was 8.07 inches in Nauvoo (Hancock County).
Another interesting feature of 2018 so far in Illinois has been the impressive precipitation totals in northern Illinois. Several stations have received over 50 inches of precipitation through October 31, including Elizabeth (Jo Daviess County) with 54.45 inches. That is 22.66 inches above normal! The maps below show the extent of the amounts over 50 inches scattered across the state (darker red), while a relatively drier band stretches from St. Louis to Chicago.