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A Warm and Dry October Ushers in Real Fall

The preliminary statewide average October temperature was 59.6 degrees, 4.8 degrees above the 1991-2020 average and tied for 9th warmest on record going back to 1895. The preliminary statewide total October precipitation was 2.61 inches, 0.65 inches below the 1991-2020 average and the 67th driest on record.  

Data are provisional and may change slightly over time.

Mild October Temperatures

October is the most quintessential fall month, weather-wise, as we transition from a more summer-like September to what is often a more winter-like November. This year, October played to type and moved from summer-like warmth in the first half to real fall days in the second half. Temperature departures from normal in Olney show daily average temperatures in the first half of the month regularly reached into the 70s, between 8 and 12 degrees above normal. A cool down around October 20th pushed most of the rest of the month’s temperatures slightly cooler than normal (Figure 1).

Figure 1. Daily October average temperatures and departures in Olney.

October average temperatures ranged from the high 50s in northern Illinois to the mid-60s in southern Illinois, between 2 and 7 degrees above average (Figure 2). High temperatures regularly reached into the high 80s and low 90s in early October, including 93 degrees in Minonk and 92 in Charleston. However, low humidity helped nighttime temperatures dip into the 20s and 30s on m any nights, including 26 degrees in Moline and 31 in Mt. Vernon.

The coolest point in the state last month was Barrington in Lake County at 55.1 degrees, and the warmest point was Morrisonville in Christian County at 64.1 degrees. Last month was a top 10 warmest October on record in several places, including Champaign-Urbana (6th warmest). Unusually high temperatures in early October broke 28 daily high maximum temperature records and 7 daily high minimum temperature records. Two places, McHenry and Normal, broke all-time October high maximum temperature records with highs of 90 and 92 degrees, respectively, in the first week of the month. Only 1 daily low minimum temperature record was broken last month.

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

Overall, the preliminary statewide average October temperature was 59.6 degrees, 4.8 degrees above the 1991-2020 average and tied for 9th warmest on record going back to 1895.

Dry North, Wet South… Again

October precipitation has a strange perception in Illinois, especially for agriculture. While our soils and streams usually need a good drink of water coming out of the summer, too much rain can delay harvest, winter wheat and cover crop planting, and other necessary fall fieldwork. This year, though, October rain was mostly not an issue because (1) harvest progressed very quickly and (2) rain was hard to come by north of Interstate 70.

The first half of October was quite dry and extended drought conditions statewide from September. A significant weather pattern shift that coincided with the mid-month cooldown brought more frequent and substantial rain, especially in southern Illinois. Overall, October total precipitation ranged from around 0.90 inches in western Illinois to over 6 inches in parts of southern and south-central Illinois. Most of the state south of Interstate 70 was 1 to 4 inches wetter than normal in October, while most of central and northern Illinois were 1 to 3 inches drier than normal (Figure 3).

Overall, the preliminary statewide total October precipitation was 2.61 inches, 0.65 inches below the 1991-2020 average and the 67th driest on record

Drought Continues in Central Illinois, Improves in Southern Illinois

Below normal rainfall continued from August and September into October in central and northern Illinois. Most of central Illinois has been 5 to 10 inches drier than normal since August 1st, less than 50% of normal over that time. The dry weather helped harvest progress very quickly, but also created some challenges with dry vegetation and high fire risk. Dozens of field fires were reported across the state in the first two weeks of October, including one that burned over 1,000 acres in north-central Illinois. Many rivers and streams remain at or near low-flow, including extremely low levels on the Sangamon and Vermilion Rivers.

In contrast, drought was eased or altogether broken in much of southern Illinois, thanks to abundant rainfall in October. The U.S. Drought Monitor released on October 28th showed significant drought improvement in southern Illinois, including many places that went from severe drought (D2) in the beginning of the month to abnormal dryness (D0) at month’s end (Figure 4).

Figure 4. U.S. Drought Monitor maps of drought in Illinois from October 7th and October 28th.

Outlooks

month of the year can bring all four seasons, including tornadoes touching down on ground with some snowpack. Quintessential November weather, though, is infinite thick clouds… break out the crock pot.

The latest outlooks from the Climate Prediction Center lean to a warmer than normal November across Illinois, but equal chances of wetter and drier than normal weather (Figure 5). A wet November would be something to be thankful for, to help with drought.

Figure 5. Maps of (left) temperature and (right) precipitation outlooks for November.

Outlooks for the period from November to January continues to lean warmer than normal, but we start to see better chances of wetter than normal conditions as we move into the heart of winter.

Figure 6. Maps of (left) temperature and (right) precipitation outlooks for November through January.
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Illinois Drought Update

Below normal rainfall has continued into fall and has both expanded and worsened drought conditions across the state. Dry vegetation and crops have caused dozens of field fires over the past two weeks. Multiple rivers have hit low- or no-flow, including the Sangamon and Vermilion, and some municipalities have begun to enact voluntary water conservation measures. The short-term forecast shows dry weather will likely persist through mid-October, and longer outlooks do not show strong signs of substantially wetter weather through at least the end of October.

Drought Intensifies as the 2025-26 Water Year Begins

Very dry weather in August, September, and the first week of October caused a significant expansion and intensification of drought across Illinois. The October 7th edition of the U.S. Drought Monitor shows at least moderate drought in 86% of the state, severe drought in 43% of the state, and a small area of extreme drought in east-central Illinois.

Maps in Figure 1 show much of central and northern Illinois were 8 to 15 inches drier than normal for the 2024-25 water year (October 1, 2024 – September 30, 2025), and parts of east-central Illinois have been 10 to 13 inches drier than normal in the 2025 calendar year.

Figure 1. Maps show (left) 2024-25 water year precipitation departures from the 1991-2020 normal and (right) calendar year 2025 to date precipitation departures from the 1991-2020 normal.

Low River Levels Across the Midwest

Drought usually affects the flow and level of small streams and creeks first, then the tributaries of our larger rivers. When dry conditions persist for weeks to months we can see low flow along our larger rivers. Persistently dry conditions have caused very low levels along many of our state’s rivers, including the Sangamon, Vermilion, Embarras, Kaskaskia, and the Illinois River.

Very low levels and flow along the Sangamon River have added to dry and warm weather to cause several central Illinois lakes and reservoirs to drop quickly. As of October 9th, Lake Decatur was 2.4 feet below the normal level and the City of Decatur has requested voluntary water conservation as the lake continues to drop.

Fire and Dust Risk

Recent rain has helped reduce field fire risk in many places. However, fire risk remains somewhat to very high, especially in central Illinois. We saw dozens of field fires across the state over the past two weeks, illustrating the continued fire risk. Extra precautions should be taken ahead of, during, and after harvest to ensure everyone stays safe considering the enhanced fire risk. You can find more information on farm fire safety here: go.illinois.edu/farmfiresafety.

Where are We Headed?

The October 7 edition of the U.S. Drought Monitor has over 86% of the state in at least moderate drought, which is up from just 6% of the state in late August. The Drought Monitor also has extreme drought (D3) in east-central Illinois for the first time since 2012.

Figure 2. US Drought Monitor current as of October 7.

Unfortunately, the next 7-days look to be dry once again across most of the state (Figure 3). Despite the recent unusually warm weather, the seasons work in our favor now, because our average temperatures will drop as we continue through fall and into winter, which will at least limit evaporation from streams and lakes. Climate Prediction Center outlooks for the third week of October show a return to unusually warm weather, with no strong signal of wetter weather in sight.

In summary: we expect drought conditions across the state will likely continue to worsen in coming weeks, albeit at a slower rate because of cooler weather and some beneficial rainfall in far southern Illinois.

Figure 3. 7-day precipitation forecast across the United States for the period October 8 to October 15.
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Fall Begins with a Warm and Very Dry September

The preliminary statewide average September temperature was 68.8 degrees, 2.0 degrees above the 1991–2020 average and tied for the 27th warmest on record going back to 1895. The preliminary statewide total September precipitation was 2.60 inches, 0.75 inches below the 1991–2020 average and the 41st driest on record.

Data are provisional and may change slightly over time.

Fall Start and Summer Finish

September is a transition month as we move from summer into fall. In very September form, the month began with a brief taste of fall-like weather. Temperatures in Monmouth were 5 to 12 degrees below normal in the first 10 days of the month (Figure 1). Summer heat returned in the latter two-thirds of September, with several days that were 5 to 15 degrees warmer than normal statewide.

Figure 1. Daily September average temperatures and temperature departures in Monmouth.

September average temperatures ranged from the high 60s in northern Illinois to the mid-70s in southern Illinois, between 2 and 5 degrees above normal (Figure 2). High temperatures regularly reached the 90s in mid- and late September, including 99 degrees in Mt Vernon and Charleston. Meanwhile, cooler air in the first half of the month brought nighttime low temperatures in the 30s across much of the state, including 37 in Lincoln and 38 in McHenry. The coolest point in the state was Stockton with an average temperature of 64.3 degrees and the warmest part of the state was Smithland Lock & Dam in Massac County with an average temperature of 72.6 degrees.

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

The summer-like heat last month broke 51 daily high maximum temperature records and 3 daily high minimum temperature records across the state. The brief cold spell in early September broke 6 daily low maximum temperature records and 17 daily low minimum temperature records. Overall, the preliminary statewide average September temperature was 68.8 degrees, 2.0 degrees above the 1991–2020 average and tied for the 27th warmest on record going back to 1895.

Another Dry Month in Illinois

September is not usually a very wet month across Illinois, but September precipitation is still important to finish the soybean crop, help along late harvested specialty crops, give our trees and other plants one last drink before winter, and keep our streams above low flow. Unfortunately, very dry conditions last month, following an extremely dry August, did none of those things. Total September precipitation ranged from less than a quarter of an inch in northwest Illinois to over 5 inches in parts of southern Illinois. Only the south seven counties were wetter than normal last month, while a large swath of central and northern Illinois were 2 to 4 inches drier than normal (Figure 3).

The preliminary statewide total September precipitation was 2.60 inches, 0.75 inches below the 1991–2020 average and the 41st driest on record.

Figure 3. Maps of (left) September total precipitation and (right) September precipitation departures from normal.

Drought Returns in Illinois

Very dry weather in August and September caused a significant expansion and intensification of drought across the state. The September 23rd edition of the U.S. Drought Monitor had moderate drought in 67% of the state and severe drought in nearly 20% of the state, when just 3 months ago only 10% of the state was in any drought level. The dry transition from summer to fall was a substantial pattern change from the extremely wet conditions in spring in southern Illinois. In fact, some areas of the south-central part of the state were having a top-5 wettest year as recently as mid-July, but has only had 10-25% of normal rainfall since then. Meanwhile, the recent dryness has only added to what has been a very dry calendar year and water year (October 1 – September 30) in parts of central and northern Illinois.

Figure 4 shows precipitation departures from normal for the 2024-25 water year (October 1, 2024 – September 30, 2025) and the 2025 calendar year so far. Most of the state north of Interstate 64 was 5 to 10 inches drier than normal in this past water year, with most of the deficit coming in the calendar year 2025. Parts of east-central Illinois, including much of Champaign County, has had over 1 foot less precipitation than normal since the start of 2025. This year to date is the 6th driest on record in Champaign and the driest since 1988. Amazingly, we’ve had 5 fewer inches of precipitation this year in Champaign than in 2012. This year to date is also the 10th driest year on record in Peoria.

Figure 4. Maps of precipitation departures from normal for (left) the 2024-25 water year and (right) the 2025 calendar year through September.

Outlooks

October – in my humble opinion – is the best weather month of the year. Days become noticeably shorter, nights become cooler, and hoodies and shorts become the fashion. However, we may need to wait a bit longer for real fall, because the Climate Prediction Center shows higher odds of a warmer than normal October (Figure 6). Unfortunately, the outlooks also show best chances of another drier than normal month in October.

The most recent outlooks for climatological winter are continuing to lean toward La Niña effects of near normal temperatures but above normal precipitation across much of the state. A wetter late fall and winter would be welcome to improve drought conditions and recharge our soils and streams. For now, let’s enjoy the best of the four seasons.

Figure 5. Temperature and precipitation outlooks for the month of October and the 3-month period between October and December.
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August Ushered us From Summer to Fall

The preliminary statewide average August temperature was 73.7 degrees, 0.1 degrees above 1991-2020 average and tied for the 59th warmest on record going back to 1895. The preliminary statewide average total August precipitation was 1.87 inches, 1.69 inches below the 1991-2020 average and tied for the 9th driest on record statewide.

Data are provisional and may change slightly over time.

It’s Hot Then It’s Cold…

The final month of climatological summer brought both summer and fall weather to Illinois. Daily average temperatures and temperature departures from normal in Aurora show the roller coaster of August weather. The month began with temperatures that were 2 to 5 degrees below normal, followed by a prolonged stretch of very warm and humid weather. A series of cold fronts in the last third of the month parked cooler Canadian air over the state, pushing some days 10 to 12 degrees below normal in late August (Figure 1). 

Figure 1. Daily August average temperatures and temperature departures in Aurora.

When we average the warm periods and cold periods in August together, average temperatures ranged from the low 70s in northern Illinois to the high 70s in southern Illinois, around within 2 degrees of normal virtually everywhere (Figure 2).

Most parts of the state pushed into the mid to upper 90s in the middle of the month, including during the State Fair. The intense heat was followed by a wonderful cooldown, and many places saw nighttime temperatures dip into the high 40s, including 44 degrees in Springfield. The warmest point in the state last month was Olmstead at 77.8 degrees, and the coolest point was Stockton at 68.8 degrees.

Overall, the preliminary statewide average August temperature was 73.7 degrees, 0.1 degrees above 1991-2020 average and tied for the 59th warmest on record going back to 1895.

Figure 2. Maps of average temperatures and average temperature departures from normal in August.

August Was Wet North and Dry South

August rainfall was much more plentiful north of Interstate-80, and virtually non-existent in some parts of southern Illinois. August totals ranged from just over 10 inches in Will County (~300% of normal) to less than a tenth of an inch in parts of south-central Illinois (Figure 3).

Carbondale only had 0.02 inches of rain the entire month making it the driest August on record there and the third driest of any month since the late 1800s. It was also the driest August on record in Mt Vernon (0.09 inches), Centralia (0.09 inches), and Charleston (0.03 inches), and the second driest in Springfield (0.16 inches) and Effingham (0.32 inches). In contrast, parts of northeast Illinois experienced a few heavy rainfall events that pushed August totals above 8 inches, including 10.5 inches in Oswego and 9.9 inches in Lake Forest.

Figure 3. Maps of (left) August total precipitation and (right) August precipitation departures from normal.

An Extremely Humid Summer in Illinois

As a cold season lover, I’m not usually remorseful for the end of summer, and this year particularly so. This past season was hot and humid to say the least. Average temperatures in June, July, and August ranged from the low 70s in northern Illinois to the high 70s in southern Illinois, between 1 and 3 degrees above normal statewide (Figure 4).

Figure 4. Maps show average temperatures and temperature departures for summer 2025.

The hallmark of this summer, though, was not a plethora of extremely hot days, but instead unrelenting humidity. The dew point temperature is a good indicator of how we experience the uncomfortable effects of high humidity. In general, Illinoisans begin to feel humidity when the dew point is above 60 degrees, begin to fell uncomfortable with a dew point above 65 degrees, and are very uncomfortable when the dew point is above 70 degrees. Much of southern Illinois spent well over half of all summertime hours with a dew point at or above 70 degrees.

Very high humidity tends to limit daytime heating but also keeps nighttime temperatures very high. Indeed, this summer’s average nighttime minimum temperatures were among the highest on record in many places, including 2nd highest on record (after 2010) in Peoria (Figure 5). Higher humidity and extreme overnight temperatures are part of longer trends in our summer climate in Illinois, as evidenced by the clear trends in summer average minimum temperatures in Peoria, where the average minimum temperature over the past 25 years is a full 2 degrees higher than the 20th Century average.

Figure 5. Summertime average minimum temperatures between 1883 and 2025 in Peoria. The orange line shows the 20th Century average summertime minimum temperature and the blue line shows the 2001-2025 average.

Overall, the preliminary summer average temperature in Illinois was 75.9 degrees, 2.1 degrees warmer than normal and tied for 11th warmest summer on record statewide.

Flooding and a Flash Drought

Week to week and month to month precipitation variability is usually at its highest in summer, but this past season was extreme even for summer. June was extremely wet in far southern Illinois and very dry in most of northern Illinois. July was extremely wet in northwest and western Illinois, and near normal elsewhere. August was bone dry in southern Illinois and extremely wet in northeast Illinois (Figure 6). The final summer total was not in the top 10 wettest or top 10 driest at any of our long-term weather stations, but precipitation extremes were nonetheless impactful last season. Those included intense rainfall and flooding in Chicago and rapid onset or “flash” drought in southern Illinois.

Figure 6. Maps show monthly precipitation departures from normal in June, July, and August.

Overall, the preliminary statewide summer precipitation total was 12.99 inches, 0.72 inches above normal and the 31st wettest summer on record.

Outlooks

September brings in what is undoubtedly the best season in Illinois, and we have already experienced some fall-like weather in August. The outlooks for the entire month of September, though, don’t give us much useful information, with equal chances of warmer and colder and drier and wetter than normal weather to kick off fall (Figure 9a). Meanwhile, guidance for climatological fall (September through November) shows stronger signs of above normal temperatures, with mostly equal chances of above and below normal fall precipitation.

Figure 9. Maps show (left) temperature and (right) precipitation outlooks for the month of September and the fall season (September through November).