Mild October Had a Chilly End

The preliminary statewide average October temperature was 56.7 degrees, 1.9 degrees above the 1991–2020 average and tied for the 31st warmest on record going back to 1895. The preliminary statewide total October precipitation was 3.46 inches, 0.20 inches above the 1991–2020 average and the 41st wettest on record.

Data are provisional and may change slightly over time.

Mild October Temperatures with Some Extremes Thrown In

For my money, October is the best weather month of the year. The summer heat mellows out and mixes with the first real shots of chilly air. We had both summer- and winter-like weather last month, but a little more of the former than the latter. As the daily temperature departures from normal in Mt. Vernon show, most October days had above average temperatures, including a few days in the final week of the month that were 15 to 20 degrees above normal (Figure 1).

Figure 1. Daily October average temperature departures in Mt. Vernon.

October average temperatures ranged from the low 50s in northern Illinois to the low 60s in southern Illinois, between 1 and 2 degrees above normal in most places (Figure 2). Most of the state saw high temperatures in the upper 80s or low 90s in early October, including 94 in Quincy and 90 in Hoopeston. The brief taste of winter in the last few days of the month brought widespread low temperatures in the low 20s, including 21 degrees in Mt. Vernon and 23 in Bloomington.

The warm periods last month broke 31 daily high maximum temperature records and an incredible 66 daily high minimum temperature records. Aledo in Mercer County broke its all-time October high temperature records last month with a high temperature of 93 degrees on October 3. The cold end to the month broke 18 daily low maximum temperature records and 37 daily low minimum temperature records. 

Figure 2. Maps of (left) October average temperature and (right) October average temperature departures from normal.

Overall, the preliminary statewide average October temperature was 56.7 degrees, 1.9 degrees above the 1991–2020 average and tied for the 31st warmest on record going back to 1895.

Dry Start and Wet End to October

The month-end precipitation totals across the state do not tell the entire story of October precipitation. The first two-thirds of the month were somewhat to very dry across the state, as most places were 1 to 2 inches drier than normal through October 24. More active weather brought multiple rounds of rain–and some snow–to Illinois, raising month-end totals near or above the 30-year normals. As Figure 3 shows, Peoria picked up more rain in the last 7 days of October than in the first 24 days, and the month ended just slightly wetter than normal in Peoria. The dry start to the month was ideal for fall harvest, while the wetter end of the month helped improve dry conditions that prevailed in August and September.

Figure 3. Plot of October daily precipitation accumulation in Peoria (shaded area) versus the normal daily accumulation (black line).

October precipitation ranged from nearly 6 inches in northeast Illinois to less than 2.5 inches in the St. Louis Metro East. Most of the state north of Interstate 70 was 1 to 2 inches wetter than normal, while areas farther south were just slightly drier, up to 2 inches drier than normal (Figure 4).

Figure 4. Maps show (left) October total precipitation and (right) October precipitation departure from average.

Last month wasn’t an extremely wet or extremely dry month anywhere in the state; however, the wetter conditions in the northern half of the state helped reduce drought extent from 23 percent of the state on October 3 to 7 percent on October 31. Small areas of western and southern Illinois remain in moderate drought due to longer-term precipitation deficits. For example, the first 10 months of the year have had the third lowest precipitation total in Quincy with 20.17 inches, around 10 inches below average. While topsoil moisture in western Illinois has improved from the wetter end of October, deeper layer moisture and water table levels remain less than ideal because of the long-term dryness.

Overall, the preliminary statewide total October precipitation was 3.46 inches, 0.20 inches above the 1991–2020 average and the 41st wettest on record.

A Spooky, Winter-y Halloween

Like all the horror film characters who inevitably run back into the haunted house, mild October temperatures lulled all of us into a false sense of security. The intense cold, wind, and for some folks, snow on Halloween was more shocking than the sound of a revving chainsaw. Halloween nighttime temperatures dipped into the low 20s and high teens across much of the state, including 18-degree lows in Monmouth and Rochelle (Figure 5). The daytime high temperatures on Halloween were the coldest on record in several spots across the state, including at Chicago’s Midway airport (37 degrees) and Mt. Vernon (43 degrees). The low temperatures on Halloween night also set records in many places, including in Kankakee (24 degrees) and Olney (22 degrees). In fact, this year was the coldest Halloween in Olney since observations began there in 1896.

Halloween snow in northern and central Illinois is not necessarily a rarity but happens once every 4 to 6 years. Measurable snow, with totals exceeding 0.1 inches, was recorded in much of the state north of Interstate 74, with totals as high as 1.5 inches in Mundelein and 0.9 inches at O’Hare (Figure 5). For reference, the average first measurable snow comes in the third or fourth week of November for most of northern and central Illinois, so this year’s event came about two to three weeks early. It’s important to note that an early snowfall does not mean we will necessarily have a very snowy winter… but this State Climatologist can hope.

Figure 5. Maps of (left) nighttime low temperatures and (right) total snowfall on Halloween. Maps are from the Lincoln National Weather Service Office: https://www.weather.gov/ilx/illinois-daily.

Outlooks

November doesn’t get the love it deserves, because it is so often associated with cloudy, blustery weather. But November typically gives us a great mix of pleasant and not-so-pleasant weather and portends the beautiful winter season in Illinois. The latest Climate Prediction Center outlooks lean into El Niño with higher chances of below normal November precipitation. November temperature outlooks are more mixed, with equal chances of warmer and colder weather this month (Figure 6).

Figure 6. Maps of (left) temperature and (right) precipitation outlooks for November.

Meanwhile, NOAA leans even more heavily into El Niño for climatological winter (December–February) outlooks (Figure 7). The outlooks show highest chances of above normal temperatures in winter, with mostly equal chances of above or below normal precipitation.

Figure 7. Maps of (left) temperature and (right) precipitation outlooks for winter (December–February).

October Brought Real Fall to Illinois

The preliminary statewide average October temperature was 53.1 degrees, 1.6 degrees below the 1991–2020 average and tied for the 40th coolest on record going back to 1895. The preliminary statewide average total October precipitation was 2.30 inches, 0.61 inches below the 1991–2020 average and tied for 52nd driest on record statewide.    

Data are provisional and may change slightly over time.

Mild October Temperatures

October 2021 was the fifth warmest on record in Illinois. The unusually warm and rainy weather last year put a damper on both harvest and fall festivities. October this year though did not disappoint fall lovers. October followed September’s lead and brought mostly mild temperatures across the state. As the temperature departures from Aurora in Figure 1 show, 16 of the first 21 days in October were cooler than normal, and many were 5 to 15 degrees below normal. Only the third week of the month had temperatures more than 10 degrees above normal. Average October high temperatures ranged from the low to high 60s, with lows in the 40s and low 50s. The result was very pleasant weather across the entire month, which, along with dry conditions, permitted a relatively quick harvest and plentiful opportunities to enjoy fall festivities.

Figure 1. Daily October average temperature departures in Aurora.

Cool October nights brought regular frost across the state, and an earlier than normal first fall freeze. For example, Du Quoin recorded its first fall 32-degree freeze on October 9, about 10 days earlier than the 1991–2020 average. Most places saw nighttime temperatures dip below the hard freeze mark of 28 degrees later in the month, including a 20-degree low in Monmouth and a 22-degree low in Carbondale.

October average temperatures ranged from the upper 40s in northern Illinois to the mid-50s in southern Illinois, between 1 and 4 degrees below normal (Figure 2). The warmest place in the state last month was Olmsted in Pulaski County with an average October temperature of 58.9 degrees. The coolest place in the state was Elizabeth in Jo Daviess County with an average October temperature of 49.2 degrees.

Figure 2. Maps of (left) October average temperature and (right) October average temperature departures from normal.

Daily high maximum temperature records were broken last month at 8 stations, and daily high minimum temperature records were broken at 1 station. Daily low minimum temperature records were also broken at 17 stations. Cairo tied its all-time October low minimum temperature record with a 25-degree low on October 19.

Overall, the preliminary statewide average October temperature was 53.1 degrees, 1.6 degrees below the 1991–2020 average and tied for the 40th coolest on record going back to 1895.

Continued Dryness Causes Issues

September was drier than normal in most places around the state, and the dryness persisted into the first two-thirds of October (Figure 3). Most areas picked up less than 1 inch of total precipitation between October 1 and 21, 1 to 3 inches less than normal over the time period.

The dryness in southern Illinois was part of a larger pattern for the Ohio and Lower Mississippi River basins. In fact, the entire Lower Ohio valley, from Louisville to Cairo, only picked up 0.60 inches of total rainfall on average between September 1 and October 21. The exceedingly dry conditions contributed to very low flows and navigation issues along the Ohio and Mississippi Rivers. Extremely dry soils particularly in southern Illinois also increased the risk of fire and forced multiple counties to impose burn bans for most of the month. Despite the bans, several wildfires and field fires broke out in southern and central Illinois in October, including a fire that burned at least 115 acres in Jefferson County. One benefit of the persistently dry conditions was that it aided a relatively smooth harvest. On the other hand, low flow and navigation issues along the Mississippi River from the dry weather has contributed to higher transportation costs and grain storage issues.

        Figure 3. Maps show (left) total precipitation and (right) precipitation departure from normal between October 1 and 21.      

The last week of the month brought wetter weather statewide, including a few places that picked up 3 to 4 inches in a single week. October total precipitation ranged from over 4 inches in southwest Illinois to less than 1.5 inches in far northwest Illinois (Figure 4). The Interstate 55 corridor between St. Louis and Chicago was the only part of the state near to slightly wetter than normal, whereas northwest and southern Illinois were 1 to 3 inches drier than normal last month.

Overall, the preliminary statewide average total October precipitation was 2.30 inches, 0.61 inches below the 1991–2020 average and tied for 52nd driest on record statewide.   

Figure 4. Maps show (left) October total precipitation and (right) October precipitation departure from normal

Outlooks

Climate Prediction Center outlooks for November mostly point to equal chances of warmer/cooler and wetter/drier than normal conditions (Figure 5). However, as we continue into our third consecutive La Niña cool season, outlooks are increasingly taking a very La Niña-esque appearance. Namely, much of Illinois is leaning toward wetter than normal conditions from December through February (Figure 6). A wetter winter would be beneficial in reducing the soil moisture deficits and improving streamflow as we move into spring.   

Figure 5. Maps show (left) temperature and (right) precipitation outlooks for November.
Figure 6. Climate Prediction Center (left) temperature and (right) precipitation outlooks for December through February.

Dry and Mild Start to Fall

The preliminary statewide average September temperature was 66.8 degrees, 0.6 degrees above the 1991–2020 average and the 57th warmest on record going back to 1895. The preliminary statewide average total September precipitation was 2.66 inches, 0.53 inches below the 1991–2020 average and the 41st driest on record statewide.    

Data are provisional and may change slightly over time.

A Mostly Mild September

September followed August’s lead and brought mostly mild temperatures across the state. As the temperature departures from Jacksonville in Figure 1 show, the only prolonged warm period last month was in the third week, when temperatures were 5 to 15 degrees above normal. A cold front swept through Illinois around the fall equinox and brought much cooler, fall-like weather to wrap up the first month of climatological fall.

Figure 1. Daily September average temperature departures in Jacksonville.

During the hot week in the third week of September, high temperatures reached into the mid- to upper 90s across the state. Among the very high temperatures was 99 degrees observed in Carbondale on Sept. 21, tied with 1940 and 1955 for the second latest 99+ degree temperature on record in Carbondale.

However, the cold front that moved through the state around Sept. 21 brought much cooler, drier air into the region. Nighttime low temperatures in the final week of the month regularly dipped into the upper 30s and low 40s. A few stations even reached the 32-degree mark in the last week of September, including the 19th earliest first fall freeze on record in Normal.

September average temperatures ranged from the low 60s in northern Illinois to the low 70s in southern, within 1 degree of normal statewide (Figure 2). The warmest place in the state last month was Bean Ridge in Alexander County with an average September temperature of 72.8 degrees. The coolest place was Stockton in Jo Daviess County with an average September temperature of 63.0 degrees.

Figure 2. Maps of (left) September average temperature and (right) September average temperature departures from normal.

Daily high maximum temperature records were broken last month at 27 stations, and daily high minimum temperature records were broken at 5 stations. Daily low maximum temperature records were broken last month at 4 stations, and daily low minimum temperature records were also broken at 4 stations.  

Overall, the preliminary statewide average September temperature was 66.8 degrees, 0.6 degrees above the 1991–2020 average and the 57th warmest on record going back to 1895.

 Drier Start to Fall

Early to mid-September brought multiple rounds of isolated, heavy precipitation to parts of northern, western, and east-central Illinois. However, significant rainfall eluded most of southern and northeastern Illinois in the first two-thirds of the month. Meanwhile, the final 10 days of the month were cooler and very dry statewide. The result was a much drier than normal September for most of southern and northeastern Illinois and near normal to slightly wetter than normal conditions in parts of northern and west-central Illinois (Figure 3). Specifically, total precipitation last month ranged from over 6 inches in parts of western and northern Illinois to less than 1 inch in far southern Illinois. Smithland Lock and Dam in Pope County recorded only 0.60 inches of rain last month, making it the fourth driest September since 1980 there.

Among the driest points in the state in September was Morton in Tazewell County, which only had 0.58 inches of rain. In contrast, the wettest point in the state in September was Warsaw in Hancock County, with 7.51 inches. One silver lining of the dry weather in the latter half of September was that it allowed a smooth start to fall harvest. However, deteriorating conditions in southern and central Illinois have resulted in an increased fire risk and concerns of low levels in the Mississippi and Illinois Rivers.     

Figure 3. Maps show (left) total September precipitation and (right) September precipitation departure from normal.                                                           

Overall, the preliminary statewide average total September precipitation was 2.66 inches, 0.53 inches below the 1991–2020 average and the 41st driest on record statewide.

The 2021-2022 Water Year

The transition from summer to fall is typically our hydrologically driest time of the year as a result of higher evaporative demand and human demand for water in summer. In contrast, the transition from winter to spring is typically our hydrologically wettest time of the year. Therefore, to best capture the seasonal variability of water availability and water balance, we denote a “water year,” which runs from October 1 to September 30. Figure 4 shows total precipitation and precipitation as a percent of normal for the 2021-2022 water year (October 1, 2021–September 30, 2022). Total water year precipitation ranged from nearly 60 inches in southern Illinois to less than 30 inches in far western Illinois. In all, water year precipitation was between 75 and 125 percent of normal statewide.

Figure 4. Maps show total precipitation and precipitation percent of normal for the 2021-2022 water year.

Outlooks

Climate Prediction Center outlooks for October lean toward warmer and drier than normal conditions statewide (Figure 5). Similarly, outlooks for the last three months of the year also lean toward warmer than normal conditions, with near normal rainfall (Figure 6).

Figure 5. Maps show (left) temperature and (right) precipitation outlooks for October.
Figure 6. Climate Prediction Center (left) temperature and (right) precipitation outlooks for October through December.

Cool Fall Temperatures Continued in October

October was much cooler and slightly drier than average across Illinois. The preliminary statewide average October temperature was 51.8 degrees, 2.6 degrees below the 30-year normal, and tied for the 19th coolest on record. Preliminary statewide average total precipitation for August was 3.03 inches, 0.21 inches less than the 30-year normal, and the 54th wettest on record.

Data are provisional and may change slightly over time

October Temperatures

Cool weather persisted from the end of September to the first week of October across the state. As the plot below of daily temperature departures from normal in Moline shows, the second week of October was 5 to 10 degrees warmer than average across the state. However, this was followed by a predominantly cooler than average second half of the month.

Eleven daily high maximum temperature records and eight daily high minimum temperature records were broken last month. Concurrently, 66 daily low maximum temperature records and 19 daily low minimum temperature records fell in October. The cool, cloudy day of October 27 broke the month’s low maximum temperature records at seven locations in Illinois. This included the 34-degree high in Kewanee in Henry County, which broke the previous October low maximum temperature record of 36 degrees, set just last year on Halloween.

The maps below show October average temperatures and their departure from the long-term average. October average temperatures ranged from the high 40s in northwest Illinois to the high 50s in southern Illinois, between 2 and 5 degrees below average. The preliminary statewide average October temperature was 51.8 degrees, 2.6 degrees below the 30-year normal and tied for the 19th coolest on record. This follows the cooler than normal months of August and September statewide.

Harvest Fires

The combination of high temperatures, very low humidity, and strong winds created a significant fire risk during the second week of October. The plot below shows a daily mean surface vapor pressure deficit, a measure of atmospheric humidity, at Springfield between January 1 and October 18 of this year (red line) compared to all previous years (gray shaded area). A vapor pressure deficit has been linked to wildfire risk, with higher vapor pressure deficit values indicating a higher risk of wildfire outbreak.

The very high values of vapor pressure deficit in Springfield, near record values on October 14, indicated a warm, dry atmosphere. Existing drought and crops drying down in fields provided ample, dry fuel for wildfire potential. Indeed, several small- to medium-sized field fires broke out across central and south-central Illinois during the second week of October.

First Snow of the Season

The map below shows the climatological earliest first measurable snowfall on record at stations across the state. The dates range from early to mid-October in northern Illinois to mid-November in southern Illinois.

The map below shows the climatological earliest first measurable snowfall on record at stations across the state. The dates range from early to mid-October in northern Illinois to mid-November in southern Illinois.

A Wet End to the Month in Southern Illinois

The first half of October was very dry for the southern half of the state, continuing a very dry September. However, around the middle of the month the atmosphere moved into a pattern more conducive to bringing precipitation into southern Illinois. Areas that received less than a tenth of an inch of rainfall in previous weeks saw widespread 4- to 9-inch precipitation totals during the final two weeks of October.

Belleville, for example, recorded its third wettest October with a total of 7.38 inches, following its wettest August and its second wettest July on record. At the end of October, Belleville was only 4 inches away from its wettest year on record, which was 2008 with 56.83 inches of rain.

Drought Continues in Central Illinois

In contrast to the wet end of October in southern Illinois, much of central Illinois ended yet another month with below average precipitation. The maps below show 30- and 180-day precipitation deficits across the state. Most of central and western Illinois received between 1 and 3 inches below average precipitation in October, adding to existing precipitation deficits from dry months in August and September.

Total six-month precipitation deficits in central Illinois exceed 7 inches in Fulton and Mason Counties and 8 inches in parts of Logan and Macon Counties. At Mount Pulaski in Logan County, for example, the June 1 to November 1 precipitation deficit of 8.47 inches is the third largest on record, smaller only than 1988 and 1893. However, it should be noted that Mount Pulaski and the surrounding areas of Logan and Macon Counties received more precipitation in the first four months of this year than in all of 1988. Therefore, drought conditions, although severe, are not nearly to the extent of those in 1988.

The most recent, October 27th version of the U.S. Drought Monitor showed continued widespread moderate drought across central Illinois in response to the rainfall deficits and below normal soil moisture and streamflow.

Outlooks

Pleasant weather is in store for the state during the first week of November. However, the Climate Prediction Center’s 8- to 14-day outlooks indicate an imminent pattern change in the second week of November, with odds moving back to below average temperatures, especially to the northwest, and above average precipitation statewide.

The most recent one-month outlooks for the entire month of November continue to show a strong La Niña influence, with elevated odds of warmer than normal conditions throughout the central U.S. and drier than normal weather in the south.

Finally, the three-month outlooks for climatological winter, December–February, show equal chances of warmer or colder than normal conditions in Illinois. However, the odds increase for wetter than normal conditions later in winter.