Author: Trent Ford

The preliminary statewide average June temperature was 74.4 degrees, 2.2 degrees above the 1991-2020 average and the 18^th warmest June on record going back to 1895. The preliminary statewide total June precipitation was 3.39 inches, 1.26 inches below normal and the 46^th driest June on record statewide.

Data are provisional and may change slightly over time.

Summer Indeed

June began with relatively mild temperatures across the state, including a few days with average temperatures that were 3 to 10 degrees below normal. However, as daily temperatures and departures from normal in Chicago show in Figure 1, summer heat kicked in mid-month and persisted until the final few days of June. Daily average temperatures between June 13 and June 25 were 5 to 15 degrees above normal in Chicago and statewide.

The heat wave in mid- to late-June was not particularly extreme in the actual temperatures. Most places in the state reached the mid- to upper-90s several days, and a few places, including Salem and Cahokia Heights, saw high temperatures above 100 degrees. However, these temperatures are not unprecedented for June. However, the heat wave was extreme in how long it lasted, with temperatures 5 to 15 degrees above normal for 10 to 14 consecutive days. For example, Charleston got above 90 degrees on half of the days in June, the most since 1988.

Overall, June average temperatures ranged from the low 70s in northern Illinois to the high 70s in southern Illinois, between 1 and 4 degrees above normal (Figure 2). Most places had daytime high temperatures in the upper 90s and a few places hit or exceeded 100 degrees during the heat wave last month. This included Mt. Vernon, which peaked over 100 degrees for the first time in June since 2012. Meanwhile, many spots in northern Illinois saw nighttime low temperatures dip into the low 40s in early June, including 41 degrees in Lisle and 43 in McHenry. The warmest place in the state last month was Cahokia Heights with an average temperature of 78.3 degrees, and the coolest place in the state in June was Waukegan with an average temperature of 70.2 degrees.

Overall, the preliminary statewide average June temperature was 74.4 degrees, 2.2 degrees above the 1991-2020 average and the 18^th warmest June on record going back to 1895.

Dry June for Most but Not All

June is typically one of the wettest months of the year in Illinois. In some years, June precipitation is consistent across the state, often the case in the wettest of Junes. This year however, the dominant weather pattern in the eastern United States was a large and persistent ridge that built up a big high-pressure system over the mid-south and southeast. The result was a persistent parade of storm systems into the Upper Midwest, causing catastrophic flooding in Minnesota, Iowa, and South Dakota, and largely hot and dry conditions in the southeast. As is often the case, Illinois was caught in between these two extremes, and June near to slightly wetter than normal in northern Illinois, and drier than normal in central and southern Illinois (Figure 3).

June totals ranged from over 8 inches in East Dubuque to only 0.63 inches in Macomb. In fact, last month was the third driest June on record in Macomb, and the driest since 1991. The preliminary statewide total June precipitation was 3.39 inches, 1.26 inches below normal and the 46^th driest June on record statewide.

Drought in Illinois

Illinois was suffering from serious drought this time last year, following extremely dry weather in May and June. By July 1, 2023 93% of the state was in moderate drought and 59% in severe drought. Thankfully, this year we’ve largely avoided serious drought conditions in the state, thanks to abundant (in some cases, surplus) precipitation in April and May. However, the stretches of hot and dry weather last month have begun to quickly deplete soil moisture and drop stream levels in much of central and south-central Illinois. The latest U.S. Drought Monitor map, current as of June 25^th, shows around half of the state is abnormally dry, and a small patch of moderate drought along the Indiana border in east-central Illinois (Figure 4).

July often makes or breaks drought in Illinois. A continuation of hot and dry conditions could accelerate drought impacts to crops, ecosystems, and water supply. However, a July like last year, with abundant (occasionally, too abundant) rainfall can quickly remove concerns of drought issues. On-the-ground reports of drought conditions and impacts are important sources of information for monitoring as we move into the second half of the growing season. Please consider reporting conditions in your area using the Condition Monitoring Observer Reporting (CMOR) system.

Severe Weather

June is one of our most active severe weather months, and while last month was not especially active with severe weather, the northern half of the state was still affected by tornadoes, hail, and severe winds. The NOAA Storm Prediction Center’s preliminary June numbers had 13 tornado reports, including an EF-1 on June 13^th that did damage outside of Gibson City in Ford County and four EF-0 tornadoes in the Chicago western suburbs on June 22^nd. Strong storms also caused several reports of storm damage from strong winds on June 16th. The airport in Moline recorded 65 mph wind gusts that afternoon.

Outlooks

July is climatologically the hottest month of the year in Illinois and can make or break a growing season with its rain (or lack thereof). The latest July outlooks from the Climate Prediction Center continue to show highest chances of above normal temperatures, but have recently leaned closer to near- if not wetter-than normal conditions (Figure 5). It’s always worth noting that July precipitation often comes in the form of isolated thunderstorms that can produce large differences in totals over small distances.

Meanwhile, outlooks for the three-month period between July and September also show highest chances of above normal temperatures and equal chances of wetter and drier than normal conditions. Concerns of Mississippi River levels in late summer and early fall — something on the minds of many after the last two years — have recently been assuaged by flooding in the Upper Midwest. However, the Ohio Valley is currently dealing with emerging drought conditions, something worth watching as we move into the climatological low-flow season for the big river.

The preliminary statewide average May temperature was 66.7 degrees, 3.5 degrees above the 1991-2020 average and the 11^th 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 42^nd 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.

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 7^th warmest May on record in the St. Louis area and in Quincy, the 10^th warmest May on record in Carbondale, and 11^th warmest May on record in Peoria.

Overall, the preliminary statewide average May temperature was 66.7 degrees, 3.5 degrees above the 1991-2020 average and the 11^th 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 3^rd warmest on record in Chicago and the 2^nd 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.

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).

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.

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.

The preliminary statewide average April temperature was 54.1 degrees, 1.5 degrees above the 1991-2020 average and tied for 28^th 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 10^th 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 20^th.

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 20^th. 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.

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 28^th 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.

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 10^th 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 2^nd and 3^rd. 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. 

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.

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).

The preliminary statewide average March temperature was 45.8 degrees, 4.4 degrees above the 1991–2020 average and the 14^th 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 60^th 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.

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 5^th warmest March on record in Peoria, the 6^th warmest in Freeport, and the 9^th 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.

Overall, the preliminary statewide average March temperature was 45.8 degrees, 4.4 degrees above the 1991–2020 average and the 14^th 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 2^nd 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 60^th wettest on record statewide.   

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).

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 8^th. 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).