Warm May Wraps Up a Very Mild Spring

The preliminary statewide average May temperature was 66.7 degrees, 3.5 degrees above the 1991-2020 average and the 11th warmest on record going back to 1895. The preliminary statewide average total May precipitation was 4.85 inches, 0.08 inches above the 1991-2020 average and the 42nd wettest on record statewide.    

Data are provisional and may change slightly over time

January to April this year was the fourth warmest start to any year on record in Illinois, with only 1921, 2012, and 2017 surpassing 2024. May continued the warm pattern across the state. Daily average temperature and departures from normal in Cahokia Heights show nearly all days last month were warmer than normal, some of which between 10 and 12 degrees above normal (Figure 1). That said, Illinois largely escaped early season extreme heat that we experienced in 2021 and 2022, making for largely pleasant temperatures last month.

Figure 1. Daily May average temperature departures in Cahokia Heights.

May average temperatures ranged from the high 50s in northern Illinois to the low 70s in southern Illinois, between 2 and 4 degrees above normal (Figure 2). Several stations saw their first 90-degree temperatures last month, including 91 degrees in Monmouth and at Chicago’s Midway Airport. Meanwhile, the state was largely spared a late spring freeze in May, with only a handful of stations experiencing temperatures below 40 degrees. Overall, the warmest place in the state last month was Du Quoin, with an average temperature of 72.5 degrees, and the coldest place in the state was Mundelein with an average temperature of 59.2 degrees. Last month was the 7th warmest May on record in the St. Louis area and in Quincy, the 10th warmest May on record in Carbondale, and 11th warmest May on record in Peoria.

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

Overall, the preliminary statewide average May temperature was 66.7 degrees, 3.5 degrees above the 1991-2020 average and the 11th warmest on record going back to 1895.

May capped off a very warm climatological spring season. Each of the three spring months brought average temperatures that were 2 to 6 degrees above normal (Figure 3). It was a top five warmest spring on record throughout virtually the entire state, including the 3rd warmest on record in Chicago and the 2nd warmest on record in Peoria. For perspective, the spring 2024 average temperature in Peoria of 56.9 degrees is a full 2 degrees less than spring 2012, illustrating just how incredibly warm spring 2012 was. Overall, the preliminary average climatological spring temperature in Illinois was 55.6 degrees which, if confirmed, would tie 2024 for the fourth warmest spring on record statewide. Only 1977, 1991, and 2012 featured warmer springs in the prairie state.

Figure 3. Maps of monthly average temperature departures from normal in March, April, and May 2024.

A Mixed Bag of May Precipitation

May is the third wettest month climatologically in Illinois, and the wettest in parts of southern Illinois. However, last month was variable across Illinois, with extremely wet conditions in far southern Illinois and near to slightly drier than normal conditions in central and northern Illinois. Specifically, total May precipitation ranged from around 3.5 inches in west-central Illinois to nearly 10 inches in parts of southeast Illinois. Most areas south of Interstate 64 were 1 to 4 inches wetter than normal last month, while areas farther north were near to 1-2 inches drier than normal (Figure 4).

Unfortunately, much of last month’s precipitation came from thunderstorms that also brought severe weather to Illinois. The NOAA Storm Prediction Center listed 24 tornado reports, 153 severe wind reports, and 56 severe hail reports in Illinois in May. Among these include an EF-3 tornado that tore through parts of Jackson and Williamson Counties, causing significant damage around the Lake of Egypt area.

Climatological spring was wetter than normal for the entire state, with totals ranging from around 12 inches in central Illinois to nearly 18 inches in far southern Illinois. Most of the state was 1 to 4 inches wetter than normal this spring (Figure 5).

Figure 5. Maps show (left) total May precipitation and (right) May precipitation departures from normal.

June & Summer Outlooks

June is the start of climatological summer and is an exciting month for many reasons. Warm weather is here, schools are out, and cicadas are buzzing (even more than usual this year). Unfortunately, the Climate Prediction Center’s June outlook is less exciting than the month’s weather. The one-month outlook is decidedly undecided in Illinois, with equal chances of warmer, cooler, drier, and wetter weather.

Figure 6. Climate Prediction Center (left) temperature and (right) precipitation outlooks for June.

The summer season outlooks (June through August) are a bit more insightful, with higher chances of above normal temperatures this summer. For precipitation, Illinois is squeezed between a band of expected drier than normal conditions to the west and wetter conditions to the east. That setup often, but not always, corresponds with active stormy weather in the summer.

Figure 9. Climate Prediction Center (left) temperature and (right) precipitation outlooks for June through August.

Warm and Wet April in Illinois

The preliminary statewide average April temperature was 54.1 degrees, 1.5 degrees above the 1991-2020 average and tied for 28th warmest on record going back to 1895. The preliminary statewide average total April precipitation was 6.14 inches, 1.9 inches above the 1991-2020 average tied as 10th wettest on record statewide.

Data are provisional and may change slightly over time.

Summer or Winter? Why not Both?

April is a transition month in Illinois, moving us from winter to summer. As with most years, last month gave us a taste of all seasons. Daily average temperatures in and departures from normal from Peoria show the ups and downs typical of April temperatures (Figure 1). The daily average temperature in Peoria went from 73 degrees on April 16 to 43 degrees on April 20th.

Figure 1. Daily April average temperature departures in Peoria.

April average temperatures ranged from the high 40s in northern Illinois to the low 60s in southern Illinois, between 1 and 4 degrees above normal (Figure 2). The prolonged period of warm weather in the middle of the month broke 14 daily high maximum temperature records and 22 daily high minimum temperature records in the state. Meanwhile, the brief shots of colder air in April broke nine daily low maximum temperature records and six daily low minimum temperature records.

Most places saw highs briefly reach into the mid-80s in the middle of the month, and a few stations around the St. Louis Metro East area flirted with 90 degrees. In contrast, most places in northern Illinois saw several nights with low temperatures dipping well into the 20s, including 21 degrees in Elgin on April 20th. Stockton was the coldest place in the state last month with an average temperature of 48.9 degrees, and Olmsted was the warmest place with an average temperature of 61.7 degrees.

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

Overall, the warmer parts of the months outweighed the colder parts, and the preliminary statewide average April temperature was 54.1 degrees, 1.5 degrees above the 1991-2020 average. If this average temperature is made official, it would be tied for 28th warmest on record going back to 1895.

April Showers

Last year April failed to bring its notorious showers and set in motion an early growing season drought in parts of Illinois. This year though, April did not disappoint those few rain lovers out there. An active storm track brought multiple waves of storms and rain across Illinois and made for the wettest month we’ve seen so far in 2024.  

April total precipitation ranged from around 3 inches in northeast Illinois to over 10 inches in southwest Illinois (Figure 2). Most of the state between Interstates 88 and 64 was 1 to 5 inches wetter than normal last month, while far southern Illinois and the northern half of Chicagoland were within 1 inch of normal April rainfall. Highland in Madison County took the April precipitation crown with 9.58 inches total, the third wettest April on record there.

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

April added to what has been a very wet start to the year for parts of northern Illinois, especially along the Interstate 80 corridor. For example, Morris has already had 15.33 inches of precipitation in 2024, the second wettest start to a year on record there. Abundant spring rain has pushed several rivers over flood stage, including the Illinois River at Havana which spent all but a few days in April above minor to moderate flood stage.

Overall, the preliminary statewide average total April precipitation was 6.14 inches, 1.9 inches above the 1991-2020 average. If that number is made official, last month will be tied as 10th wettest on record statewide.

More Snow No One Wants

The first 80-degree day in many parts of Illinois is on par with any of the great weather gifts we have, like a Christmas morning snow or an October afternoon with winds below 20 mph. But if you’ve lived in Illinois for more than a year, you should be weary of the snow that inevitably follows that first taste of summer temperatures. Alas, a storm system snuck measurable snow into northern Illinois on April 2nd and 3rd. Totals ranged from just over a tenth of an inch as far south as Peoria to over 4 inches in eastern Jo Daviess County.

Thankfully, the latter half of the month came without measurable snowfall, leaving most of the state south of Interstate 74 snowless for April (Figure 3). I will not pronounce the snowfall season to be over as that would only doom us for a rare (but possible) May snow. I will say that the likely end-of-season snowfall in Illinois is only near to above normal in the northwest corner, thanks to a very heavy January snowstorm. Meanwhile, the northeast part of the state was 10 to 20 inches below normal snowfall in the 2023-24 snow season. 

Figure 4. Maps show (left) April snowfall totals, (middle) April snowfall departures from normal, and (right) October to April snowfall departures from normal.

Outlooks

Even though April can give us a taste of summer, May is the first month where we really experience summer weather. Last year’s May was the driest statewide since 2012, but May outlooks from the Climate Prediction Center show highest chances for near to above normal precipitation this month in Illinois (Figure 5). There remain higher chances of above normal temperatures in May as well.

Figure 5. Maps show (left) temperature and (right) precipitation outlooks for May.

Outlooks for the period from May through July looks similar, with highest chances for above normal temperatures and precipitation to kick off the growing season (Figure 6).

Figure 6. Maps show (left) temperature and (right) precipitation outlooks for May-July.

Warm and Dynamic March Opens Spring

The preliminary statewide average March temperature was 45.8 degrees, 4.4 degrees above the 1991–2020 average and the 14th warmest on record going back to 1895. The preliminary statewide average total March precipitation was 3.09 inches, 0.15 inches above the 1991–2020 average and the 60th wettest on record statewide.    

Data are provisional and may change slightly over time

Mild Start and Bumpy End to March

Mild temperatures from February carried over to the first half of March in Illinois. Most of the first 15 days of March were warmer than normal in the state, including in Fairfield (Figure 1). A strong storm system pulled in very warm and humid air from the Gulf of Mexico on March 5, sending high temperatures into the 70s and 80s across the state. However, the second half of the month had more days with below normal temperatures and multiple rounds of sub-freezing nighttime low temperatures.

Figure 1. Daily March average temperature departures in Fairfield.

March average temperatures ranged from the low 40s in northern Illinois to the low 50s in southern Illinois, between 2 and 5 degrees above normal (Figure 2). The warmest place in the state last month was Du Quoin at 53.4 degrees on average, and the coldest place in the state last month was Stockton at 39.6 degrees. It was the 5th warmest March on record in Peoria, the 6th warmest in Freeport, and the 9th warmest in both Moline and Rockford.  

The mild weather in the first half of the month broke 77 daily high maximum temperature records and 32 daily high minimum temperature records in Illinois. The colder weather that settled in the back half of March broke three daily low minimum temperature records, including 21 degrees in Kaskaskia.

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

Overall, the preliminary statewide average March temperature was 45.8 degrees, 4.4 degrees above the 1991–2020 average and the 14th warmest on record going back to 1895.

Mixed Wet and Dry Conditions in March

The first two months of the year included a top 15 wettest January on record and the 2nd driest February on record in Illinois. March gave us a little taste of both worlds, with wetter conditions in the north and drier conditions in the south. March total precipitation ranged from over 6 inches in north-central Illinois to less than 2 inches in southern Illinois. Most of the state north of Interstate 70 had a near-normal to wetter than normal March, while much of southern Illinois was 1 to 3 inches drier than normal (Figure 3).

Overall, the preliminary statewide average total March precipitation was 3.09 inches, 0.15 inches above the 1991–2020 average and the 60th wettest on record statewide.   

Figure 3. March total precipitation (left) and March precipitation departure from normal (right).

Uh Oh, March Hail and Snow

Unfortunately, not all March precipitation was rain. While March wasn’t nearly as active for severe weather as last year, we did get quite a bit of hail across Illinois. The Storm Prediction Center’s preliminary count had 68 severe hail reports across Illinois last month, including eight reports of 2-inch (i.e., hen egg size) or larger diameter hail. If you feel like Illinois has had a lot of hail in the month of March recently, you’re not wrong. Each of the last two years have had more than 45 severe hail reports across the state, following a stretch of five years between 2018 and 2022 with only 37 severe hail reports total.

Meanwhile, as it often does, March brought some snowfall to northern Illinois. Most places north of Interstate 80 saw some accumulation in March, with some isolated 8- to 9-inch totals in Boone and McHenry Counties. Despite the impressive totals, March still ended with below normal snowfall for the entire state, adding to deficits from the rest of the snow season (Figure 4).

Figure 4. Maps show (left) total March snowfall, (middle) March snowfall departure from normal, and (right) season-to-date snowfall departures from normal.

April & Late Spring Outlooks

April is an important weather month in Illinois because it ushers in a typically wet three-month period that also brings the highest threat of severe weather. April is also when we see spring fieldwork and planting in earnest across the state. And this year, April is particularly interesting because of the solar eclipse on the 8th. I’ll refer to the National Weather Service for an official eclipse forecast, and instead present the outlooks for April and the three-month period between April and June.

The final April outlook from the Climate Prediction Center has highest chances of warmer and wetter than normal conditions in this important month (Figure 5). The April-June period also leans warmer and wetter than normal in Illinois (Figure 6).

Figure 5. Climate Prediction Center (left) temperature and (right) precipitation outlooks for March.
Figure 6. Climate Prediction Center (left) temperature and (right) precipitation outlooks for April through June.

Another Mild February Ends Another Weak Winter

The preliminary statewide average February temperature was 39.4 degrees, 8.3 degrees above the 1991–2020 average and the 3rd warmest on record going back to 1895. The preliminary statewide average total February precipitation was 0.53 inches, 1.58 inches below the 1991–2020 average and the 4th driest on record statewide.    

Data are provisional and may change slightly over time

Extremely Mild February

Climatologically, February is the second coldest month statewide after January. February 2023 was very mild, about 4 degrees above normal. However, last month made February 2023 look like an Arctic blast.

Figure 1 shows daily temperature departures from normal in Monmouth in February. Only three days in our 29-day month were colder than normal, while most days were 10 to 30 degrees warmer than normal.

Figure 1. Daily February average temperature departures in Monmouth.

February average temperatures ranged from the mid-30s in northern Illinois to the high 40s in southern Illinois, between 6 and 12 degrees above normal (Figure 2). Several stations saw daily high temperatures in the 80s last month, including 83 degrees in Belleville and 80 in Springfield. A strong cold front in the last week of the month dropped temperatures from the 70s and 80s into the teens and 20s. Several places saw 50- to 60-degree declines in less than 24 hours. Overall, the warmest place in the state last month was Du Quoin, with an average temperature of 49.1 degrees, and the coldest place in the state was Stockton in Jo Daviess County with an average temperature of 34.8 degrees.

The mild weather in February broke 186 daily high maximum temperature records. These included a 75-degree high in DeKalb on February 28, which beat the previous daily high record by a full 12 degrees. There were also 43 daily high minimum temperature records broken last month. Twenty-two locations in Illinois set new all-time February high temperature records, including 77 degrees in Peoria, 77 in Charleston, 76 in Moline, and 73 in Rockford. Last month was the warmest February on record in Chicago, Rockford, Moline, and Peoria. It was a top 5 warmest February virtually everywhere in the state. 

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

Overall, the preliminary statewide average February temperature was 39.4 degrees, 8.3 degrees above the 1991–2020 average and the 3rd warmest on record going back to 1895.

The Winter That Mostly Was Not

February ended yet another very mild climatological winter season that featured only one truly cold air outbreak. The season began with the 3rd warmest December on record statewide, followed by a mostly mild January split in two by extreme cold. An incredibly mild February put a cap on a winter with average temperatures that were 4 to 8 degrees above normal in Illinois (Figure 3).

Overall, the preliminary statewide average winter temperature was 34.8 degrees, 5.1 degrees above the 1991–2020 normal and, if confirmed, would be the 3rd warmest winter on record in Illinois.

Figure 3. Maps of (left) winter average temperature and (right) winter average temperature departures from normal.

This is the part of the summary where I, once again, lament the long-term winter warming trend in Illinois. Winter is warming faster than any other season and is one of the most consistent impacts of human-caused climate change in the Midwest.

With respect to the long-term historical record, the 2022–2023 winter season was unusually warm. However, the season is part of a long-term warming trend that is larger in winter than in any other season across Illinois. Winter warming is one of the most consistent impacts of anthropogenic climate change in Illinois, driven by human greenhouse gas emissions. As Figure 4 shows, the statewide average winter temperature has increased by about 0.20 degrees per decade since 1895, and the average winter temperature over the past 30 seasons is about 2 degrees warmer than the 20th century average. One of the consequences of this long-term warming trend is a higher chance of warm winters that would be considered unusual based on the 20th century numbers. For example, six of the top 10 warmest winters on record in Illinois have occurred since 2001–2002.

Figure 4. Plot shows statewide average winter temperatures in Illinois (blue line) and the long-term trend in winter average temperatures (black line).

Very Dry February

February is one of the climatological driest months of the year, and the last month fit that mold. Total February precipitation ranged less than half an inch in parts of western Illinois to around 3 inches in parts of northern Illinois (Figure 5). Most of the state was 1 to 3 inches drier than normal last month, while only a narrow stretch of northern Illinois caught more than normal precipitation.

Figure 5. February total precipitation (left) and February precipitation departure from normal (right).

Last month was the 7th driest on record in Rockford (0.29 inches total), the 8th driest in Moline (0.26 inches total), the 6th driest in Springfield (0.51 inches total), the 3rd driest in Normal (0.14 inches total), the 3rd driest in Quincy (0.07 inches), and 4th driest in Carbondale (0.74 inches). In fact, February tied for the 7th driest month on record (for any month) in Quincy, whose record stretches back to 1901. Overall, the preliminary statewide average total February precipitation was 0.53 inches, 1.58 inches below the 1991–2020 average and the 4th driest on record statewide.   

The very dry February in Illinois followed a very wet January and a mixed bag of wetter and drier than normal conditions in December. Overall, winter total precipitation ranged from less than 5 inches in northwest Illinois to over 10 inches in far southern Illinois. Most areas north of Interstate 64 were near to 1 to 2 inches wetter than normal last season, while far southern Illinois was 1 to 2 inches drier than normal in winter (Figure 6).

Figure 6. Maps show total precipitation departures from normal for (left) fall 2022 and (right) winter 2022–2023.

I Remember Snow…

I am contractually obligated to remind everyone that Illinois often – if not normally – gets some measurable snowfall in March and occasionally in April. So, the “snowfall season” is not yet complete; however, January and February almost always contain the most snowfall in the state. The first two months of 2024 underproduced in the snowfall category for virtually everyone outside of the Quad Cities and the northwest corner of the state.

February total snowfall ranged from less than two-tenths of an inch in northwest Illinois to just over 5 inches in central Illinois. Only the Interstate 70 corridor was above normal on February snowfall, while most of northern Illinois was 4 to 10 inches below normal (Figure 7). The big January snowstorm in the Quad Cities area keeps that region above normal on season-to-date snowfall, while most of the rest of the state is 5 to 15 inches behind normal snowfall by March 1.

Figure 7. Maps show (left) total February snowfall, (middle) February snowfall departure from normal, and (right) season-to-date snowfall departure from normal.

March & Spring Outlooks

March is the first month of climatological spring, and the first month we typically begin to see signs of spring. Of course, spring started weeks ago this year. The Climate Prediction Center temperature outlooks lean warmer than normal across the state. A warmer March will continue our sprint to an early spring, for good or for bad. Precipitation outlooks indicate equal chances of wetter and drier than normal conditions in March. As much as dry soils can help facilitate spring fieldwork, we could use a wetter March to help improve slowly worsening drought conditions, especially in southern Illinois.

Figure 8. Climate Prediction Center (left) temperature and (right) precipitation outlooks for March.

The spring season outlooks (March–May) also show slightly higher chances of above normal temperatures. Meanwhile, the higher chances of wetter spring conditions in the southeast US reaches up and grabs part of Illinois.

Figure 9. Climate Prediction Center (left) temperature and (right) precipitation outlooks for March through May.