October brought record-breaking heat and cold and snow to Illinois

[November 10, 2019]    October temperatures soared from record-breaking heat during the first week and fell to record-breaking cold at the month’s end in Illinois, according to Illinois State Climatologist Trent Ford at the University of Illinois’ Illinois State Water Survey. The first snow of the season fell on or before Halloween.

The preliminary statewide October average temperature was 53.7 degrees, less than 1 degree below the 30-year normal.

Record-breaking high temperatures persisted from September into early October. Average temperatures during the first four days of October were 10 to 14 degrees above normal in the southeast part of the state and 3 to 8 degrees above normal in the northwest.

Maximum temperatures broke 90 degrees and minimum temperatures remained in the 70s for several days in southern Illinois. Stations in Saint Clair and White Counties reached 96 degrees on October 2.

Between October 1 and 4, 46 daily high maximum temperature records and 73 daily high minimum temperature records were broken across Illinois, according to the National Centers for Environmental Information (NCEI). Additionally, 9 stations broke their all-time October high maximum temperature records, and 13 stations broke their all-time October high minimum temperature records.

In one particularly extreme event, the October 1 nighttime minimum temperature at Kaskaskia Lock and Dam in Randolph County was 72 degrees, 10 degrees above the previous daily record and 2 degrees above the all-time October minimum temperature record at that station.

Seasonable temperatures were reported after the heat was broken toward the end of the first week of October. Temperatures from October 5 to 27 were near normal in eastern Illinois and between 3 and 6 degrees below normal for western Illinois.

Nearly all the state experienced the first fall frost event in the second week of October. Nighttime minimum temperatures dipped below 32 degrees as far south as Pope County and below 28 degrees in Warren and Jo Daviess Counties.

Temperatures between October 28 and 31 were 8 to 16 degrees below normal. Similarly, 44 daily low maximum temperature records and 8 daily low minimum temperature records were broken across Illinois over the last four days of the month. Nighttime minimum temperatures dropped below 30 degrees as far south as Pulaski County.

The lowest minimum temperature observed in October was 14 degrees, both in Carroll County and Lee County on Halloween night. This year was the coldest Halloween for 51 stations around Illinois.

October precipitation was above normal for most of the state and slightly below normal for west-central Illinois. The statewide total precipitation in October was 5.20 inches, approximately 2 inches more than the 30-year normal. Areas of far northern and southern Illinois received over 6 inches of rainfall in October, with isolated locations of more than 10 inches.

Stations in New Lenox in Will County and Riverwoods in Lake County recorded over 12 inches of precipitation in October.

Significant rainfall helped improve drought conditions in southern Illinois. The latest U.S. Drought Monitor map for October 29 shows no drought in Illinois for the first time since early August.

Snow fell with some accumulation in northern and western Illinois. Total snowfall accumulation over the last week of October ranged from over 8 inches in northwestern Illinois to just over a tenth of an inch as far south as Nokomis in Montgomery County.

The highest October snowfall total, 8.5 inches, was in Orangeville in Jo Daviess County. Although late October is early for the first snowfall in Illinois, this isn’t the first time it has happened.

Short-term 8- to 14-day outlooks from the Climate Prediction Center show strong odds of below normal temperatures persisting into the first couple of weeks of November. Below normal precipitation is expected out to 14 days, as drier weather is likely to prevail following the first winter storm of the season in Illinois.

Longer-term outlooks for November also show increased odds of below normal temperatures and increased odds of above below normal precipitation. Winter (December–February) outlooks show greater odds of a wetter than normal winter.

[Lisa Sheppard]