Fall – Illinois State Climatologist

November 1, 2022November 1, 2022

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 40^th 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 52^nd 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 40^th 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 52^nd 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 6**. Climate Prediction Center (left) temperature and (right) precipitation outlooks for December through February.

October 3, 2022October 3, 2022

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 57^th 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 41^st 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 19^th 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 57^th 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 41^st 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.

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 6**. Climate Prediction Center (left) temperature and (right) precipitation outlooks for October through December.

November 3, 2020

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 19^th 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 54^th 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 19^th 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.

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 27^th 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.

October 1, 2020

A Cool Start to Fall

September was slightly cooler and wetter than average across Illinois. The preliminary statewide average September temperature was 65.4 degrees, 0.8 degrees below the 30-year normal, and tied for the 45^th coolest on record. Preliminary statewide average total precipitation for August was 3.39 inches, 0.16 inches more than the 30-year normal, and the 58^th wettest on record.

Data are provisional and may change slightly over time

September Temperatures

A cold front moved through the Midwest in late August, bringing Illinois its first real taste of fall air. Below average temperatures remained in place for most of September, resulting in an overall statewide average temperature of 65.4 degrees, 0.8 degrees below the 30-year normal.

The maps below show September average temperatures and their departure from the long-term average. September temperatures ranged from the low 60s in northern Illinois to the low 70s in far southern Illinois. All but the very northeastern corner of the state was cooler than average, including parts of Putman and LaSalle Counties, which were nearly 3 degrees below the long-term September average temperature.

September Temperatures

Although temperature departures were largest in northern Illinois, the southern half of the state experienced unusually cold weather during the third week of September. The map below shows observed minimum temperatures on September 20. The station in Cairo in Alexander County observed 37 degrees that morning, which broke the all-time September minimum temperature record in Cairo set in 1989.

Western U.S. Wildfire Smoke

On several otherwise cloud-free days last month, the sky over Illinois appeared an odd milky-white color. This was caused by smoke from wildfires in the western U.S. that had moved across the country. The figure below shows a satellite estimate of vertically integrated smoke across the U.S. on September 17. Areas with relatively high smoke content in the atmosphere are shown in red and pink. Although the smoke created an eerie appearance in the sky, it did not pose a health risk to Illinoisans. The smoke though did likely, although modestly, suppress our daytime high temperatures last month as it reduced the amount of sunlight reaching the surface and heating the afternoon air.

Southern Illinois’ Turn for Drought

September statewide total precipitation was 3.39 inches, approximately 0.16 inches above the long-term average. However, much like the previous three months, large precipitation gradients created rainfall winners and losers. The maps below show total September precipitation and September precipitation percent of normal.

Total September rainfall ranged from over 9 inches in northwest Illinois to less than a half inch in eastern Illinois. Most areas of northern Illinois experienced between 125 percent and 300 percent of normal September precipitation, while areas of southern Illinois experienced between 10 percent and 90 percent of normal.

On one end of the extreme, the station at the Quad Cities airport in Moline experienced its 10^th wettest September with a total of 6.25 inches. This followed the driest August on record in Moline, with only 0.15 inches of total August precipitation. This is contrasted by the station in Paris in Edgar County, which observed only 0.34 inches of total precipitation in September, making it the third driest September on record in Paris. This came after the second wettest July on record in Paris, with over 10 inches of precipitation.

However, Belleville in St. Clair County wins the prize of most variable rainfall over the past few months with the second wettest July on record, followed by the wettest August on record, followed by the seventh driest September on record.

The rainfall in northern Illinois was welcome, and alleviated drought conditions that had persisted there since early August. However, the very dry conditions in central and southern Illinois resulted in an expansion of moderate drought and abnormally dry conditions in the most recent, October 1 edition of the U.S. Drought Monitor (map below).

Outlooks

The first few days of October have continued the cool weather in September. However, outlooks from 6 to 10 days out to 3 months are indicating the highest odds for warmer than normal conditions.

The 8- to 14-day outlooks below indicate strongly elevated odds of warmer and drier than normal conditions in the second week of October across the state. Although this will not help alleviate ongoing drought in central and southern Illinois, it will help crop dry down as we enter the peak harvest season.

Looking farther out, the week three to four outlooks are similar with warmer and drier than normal conditions prevailing for the latter part of October.

As we begin to look toward climatological winter, the three-month outlooks for November, December, and January are still tilted toward warmer than normal conditions. Precipitation outlooks for the same three-month period show an equal chance of wetter and drier than normal weather.