Drought re-intensified in Illinois at the end of the growing season and has increased the fire and blowing dust risk as we approach harvest. River levels have also dropped near or below low stage, increasing concerns of issues with navigation.
Working off Early August Rains
The drought peaked in early July for much of Illinois, as more active, stormy weather was present most of that month and in the first two weeks of August. Most of Illinois was 1 to 8 inches wetter than normal between mid-July and mid-August, dramatically improving soil moisture, crop conditions, and streamflow. However, drier weather has dominated since mid-August, and most of central and northern Illinois have been 1 to 4 inches drier than normal between mid-August and mid-September (Figure 1).
Soil moisture down to 20 inches has been depleted once again because of the below normal rainfall. The combination of dryness and late August heat has also sped up crop senescence and possibly affected some yields in the driest parts of the state. Meanwhile, crops in areas of the state that had been wetter in early August, such as parts of central and southern Illinois, have been relying on the remaining soil moisture.
Water table levels have also dropped across the northern two-thirds of the state as soil moisture is used. Water table levels at the State Water Survey’s WARM station in Freeport dropped more than 1 foot between August 1 and September 1 (Figure 2), and current water table depths are 1.5 feet deeper than this time last year.
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 like the Illinois, Rock, and Kaskaskia. When those drought conditions cover most of the Midwest region, we can see low flow along the region’s largest rivers like the Mississippi and Ohio. Persistently dry conditions this summer have caused concerns of low flow conditions along the Mississippi River, like the issues we saw last fall. As of September 15, the Mississippi at Memphis was 4 feet below low stage and forecasted to approach record low values by late September. The big river hit a record low of -10.81 feet on October 21, 2022, so it is concerning that we are approaching these low values a full month ahead of last year.
The problem of big river low flow is not as easily fixed as soil moisture drought. Most rain over the next few weeks would be soaked up by the soil to replenish soil moisture and groundwater, reducing runoff to the big rivers and their tributaries. Therefore, the Midwest region will need prolonged wetter conditions over the next several weeks to help reduce or avoid the impacts of low flow on our rivers.
Where are We Headed?
The September 12 edition of the U.S. Drought Monitor has over 20% of Illinois and nearly half of the Midwest region in at least moderate drought (Figure 3). Most of the worst drought issues are in the western Midwest, while the eastern corn belt remains mostly drought-free.
Next week looks to be very dry across most of the region, including the Ohio Valley region that often contributes significantly to the flow of the Ohio and lower Mississippi Rivers (Figure 4). Beyond that, outlooks show the best chances of warmer conditions returning for the last full week of September, but also possibly better chances of near to wetter than normal conditions in the Midwest.
Fire and Dust Risk
We are still a few weeks from harvest in full swing, but more combines are out of the shed–and some in the field–across southern and central Illinois. Recent dry weather has quickly dried corn and beans, and combined with low humidity and dry topsoil, has increased field and grass fires across the Midwest. 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.
Additionally, the dry crop and topsoil increase the chances of blowing dust on dry and windy days. Folks should consider weather conditions and the potential dust created when harvesting. We want to avoid dangerous blowing dust situations like what we saw this spring.
The preliminary statewide average August temperature was 73.5 degrees, 0.1 degree above the 1991–2020 average and tied for the 63rd coolest on record going back to 1895. The preliminary statewide average total August precipitation was 4.43 inches, 0.87 inches above the 1991–2020 average and the 29th wettest on record statewide.
Data are provisional and may change slightly over time.
Big August Heat, but Mild Weather Overall
The final month of climatological summer had mild temperatures overall, except for a very intense heat wave in the third week of August. Daily average temperature departures from Normal, IL show most August days were within 7 to 8 degrees of their normals, and more than half of August days were cooler than normal in the twin cities (Figure 1).
August average temperatures ranged from the low 70s in northern and central Illinois to the high 70s in southern Illinois, within 1 degree of normal statewide (Figure 2). Most parts of the state pushed into the mid- to upper 90s on August 24 and 25, and Chicago’s O’Hare airport recorded 100 degrees on August 24 for the first time in 11 years. The intense heat was followed by a fleeting taste of fall air, and many places saw nighttime temperatures dip into the high 40s, including 48 degrees at Marseilles. The warmest point in the state last month was Cahokia at 77.4 degrees, and the coolest point was Stockton at 69.7 degrees.
Overall, the preliminary statewide average August temperature was 73.5 degrees, 0.1 degrees above the 1991–2020 average and tied for the 63rd coolest on record going back to 1895.
Late Season Heat Wave
This summer will not go in the books as a particularly extreme season temperature-wise. Most parts of the state have seen near to slightly fewer than normal days with high temperatures exceeding 90 degrees, and early season drought helped nighttime low temperatures regularly drop out of the 70s. However, the largely mild weather was broken up by two intense heat waves, one in late July and the other this past month. A large upper-level ridge established over the central U.S. around August 20, bringing very warm air and high humidity from the southern U.S. and Gulf of Mexico. Daily high temperatures exceeded 95 to 100 degrees across most of the state on August 23 and 24 (Figure 3), and, combined with the humidity, pushed heat index values over 110 degrees statewide. Peoria set a new heat index record at 121 degrees, breaking its previous record from 1995.
The heat caused buckled roads in parts of central Illinois, stressed air conditioning units, and significantly increased energy demand across the Midwest. Both Champaign and Urbana schools were forced to close on August 24 due to malfunctioning HVAC systems and dangerously high temperatures inside some schools.
Drought Relief for Some in August
July brought some better rain to parts of drought-stricken Illinois, yet moderate drought remained in more than half the state coming into August. A more active storm track last month helped bring in multiple systems that brought wetter weather to central and southern Illinois in August, helping to continue to relieve earlier drought conditions. Total August rainfall ranged from less than 2 inches in parts of northwest Illinois to over 10 inches in southeast Illinois (Figure 4). Most areas of the state south of Interstate 80 were 1 to 5 inches wetter than normal in August, while much of northern Illinois was 1 to 3 inches drier than normal.
The dryness last month was most intense in northwest Illinois from the Quad Cities to the Wisconsin border. Freeport had its third driest August on record with only 0.80 inches–about 3 inches drier than normal–and the driest last month of summer since 1966. Meanwhile, Fairfield in southeast Illinois had its fourth wettest August on record with 8.11 inches.
Overall, the preliminary statewide average total August precipitation was 4.43 inches, 0.87 inches above the 1991–2020 average and the 29th wettest on record statewide.
Drought in Illinois
It’s safe to say that drought reached a peak in early July, and conditions across much of the state have improved since then. The August 29 U.S. Drought Monitor map has 16 percent of the state in at least moderate drought compared to over 50 percent on August 1 (Figure 5). The wetter weather in August helped improve crop and pasture conditions across the state, stabilize declining streams and pond levels, and promote ecological health in our natural lands. Despite the recovery, drought likely and significantly impacted crop yield potential this year, and its impact on tree health–especially in urban areas–will not be well known until next year. However, rain in July and August helped keep 2023 out of the same breath as the most severe drought years like 2012 and 1988. One exception to the wider drought improvement is in northwest Illinois, where drought conditions expanded in August. Crop impacts have been reported in this part of the state through August, and soils remain somewhat to very dry from the Quad Cities up to Rockford.
While drought has largely improved in Illinois, its impact to flow on the Midwest’s largest rivers remains. Dry conditions in the Upper Mississippi and Ohio Basins have led to concerns of low flow and navigation and ecology impacts along the Mississippi River. Forecasts indicate the Mississippi River at Memphis is likely to reach low stage in early September (Figure 6). Dry soils across the larger Midwest region will likely slow river stage recovery from any additional rain in early fall. Therefore, without a significant shift to wetter conditions and/or an errant tropical system moving into the region, low flow issues on the Ohio and Mississippi Rivers are likely to continue or intensify into September.
Summer in Illinois
Climatological summer encompasses June, July, and August, and the season often brings more than its fair share of intense weather. This past season was on the mild side, temperature-wise, and was somewhat to much drier than normal. The abundance of gray in the maps in Figure 7 indicates average temperatures in all three summer months were mostly within 1 degree of normal across the state. While the Midwest was exposed to ephemeral heat in July and August, persistent extreme high temperatures stayed well south, making for one of the hottest summers on record in parts of Texas and New Mexico.
The summer season began with a very dry June that kicked off drought concerns across the state. Wetter conditions in July and August helped reduce or eliminate drought in central and southern Illinois, but parts of northern Illinois remained dry in the latter part of the season. Summer precipitation totals ranged from 6 inches in parts of northwest Illinois to over 20 inches in parts of southeast Illinois. Most of the northwest part of the state was 4 to 8 inches drier than normal in summer, while much of southern Illinois was 2 to 10 inches wetter than normal (Figure 8).
This past season was the 13th driest summer on record in Moline with 6.89 inches, and the driest since 2012. It was also the 20th driest summer on record in Rockford with 7.63 inches, which is less than half of the summer total from last year. Three of the past four years have seen top 20 driest summers in Rockford. In contrast, this summer was one of the wettest in far southern Illinois, and it was the fifth wettest on record in Paducah, Kentucky with 18.90 inches.
Overall, the preliminary statewide average summer temperature was 73.4 degrees, 0.4 degrees below the 1991–2020 average and tied for the 57th coolest on record going back to 1895. The preliminary statewide average total summer precipitation was 11.51 inches, 0.76 inches below the 1991–2020 average and the 69th driest on record statewide.
September brings in what is undoubtedly the best season in Illinois. However, outlooks for the month of September suggest we may need to wait a bit for more consistent fall weather, with higher odds of warmer and drier than normal weather for the first month of the season (Figure 9a). Meanwhile, guidance for climatological fall is less than confident, with equal chances of warmer, cooler, wetter, and drier than normal weather.
The 2023 drought has been the most extensive and intense in Illinois in the last 10 years. In mid-July, two-thirds of the state was in at least moderate drought, which caused significant impacts to crops, ecology, streams and rivers, and lake levels. Fortunately, most of the state has been considerably wetter since mid-July, providing some relief to drought conditions.
Most of the state saw near to much wetter than normal conditions since mid-July (Figure 1). Isolated spots of central Illinois and virtually all of far southern Illinois was 5 to 8 inches wetter than normal over the past 30-days, while much of central and northeast Illinois were 1 to 3 inches wetter than normal. Some parts of northwest and central Illinois remained 1 to 2 inches drier than normal since mid-July, but the combination of at least some rain and mild temperatures helped reduce drought extent and severity statewide.
The recent wetter conditions have helped improve drought extent and severity. The August 15th US Drought Monitor map shows only 15% of the state in at least moderate drought, down from 65% in mid-July and over 90% in late June (Figure 2). The quick improvement in the Drought Monitor over the past 4 weeks matches the rapid onset of this year’s drought between that was driven by a very dry June.
Heat and Dryness on the Way
Soil moisture has increased substantially across the state in the first half of August. Having plant available water in the soil will be particularly improvement as we head to a period of very hot and dry weather in Illinois. The 7-day Weather Prediction Center forecast shows very little, if any rain coming to Illinois through August 24 (Figure 3). The dryness is due to a very large area of high pressure that will likely set-up in the central US. The big weather change will also bring in much higher temperatures, with daily highs possibly in the mid- to upper-90s for several days. The combination of dry and hot weather will stress crops and ecology, which is why our wetter soils are so important moving into next week.
It’s important to note that some parts of the state have not seen as much improvement since the beginning of August, and we’ll likely see drought impacts worsen in those places next week.
Beyond next week, the latest Climate Prediction Center outlooks show higher chances of drier than normal conditions in northern Illinois and much of the Upper Midwest carrying over into September (Figure 4). September and October tend to be the time of the year with the overall lowest streamflow on large rivers such as the Mississippi and Illinois. Recent rain has greatly improved streamflow conditions along these and other rivers, but a potential shift to drier conditions in the Upper Mississippi basin could increase the risk of low-flow conditions south of St. Louis or Cairo moving into fall. This is something to watch as we move into September.
As we move ahead into a hot and dry week, and farther out as summer transitions to fall, it is very important to continue monitoring and reporting drought conditions and impacts. Folks should continue reporting what they’re seeing from drought using the Condition Monitoring Observer Reporting (CMOR) system: go.illinois.edu/cmor.
The preliminary statewide average July temperature was 75.3 degrees, 0.1 degrees below the 1991–2020 average and tied for 64th warmest on record going back to 1895. The preliminary statewide total July precipitation was 5.08 inches, 1.02 inches above the 1991–2020 average and the 22nd wettest on record.
Data are provisional and may change slightly over time.
Mostly Mild July Capped by Big Heat
July began with a mix of slightly warmer conditions followed by a prolonged period of near to below normal temperatures. Temperature departures from Dixon showed a nearly three-week period where all but one day was cooler than normal in the middle of July (Figure 1). A large ridge over the southwest U.S. that kept a pleasant, northwest flow of cooler air into the Midwest for most of the month opened in the last week of July, building intense heat across the region between July 26 and 29. More details on the late July heatwave follow.
July average temperatures ranged from the low 70s in northern Illinois to the high 70s in southern Illinois, within 1 degree of normal virtually everywhere (Figure 2). The welcomed lack of humidity in the first two-thirds of the month allowed nighttime low temperatures to regularly dip into the low 60s and even 50s in some parts of the state. July nighttime lows included 51 degrees in Aurora, 53 in Chenoa, and 54 in Ottawa. Daily high temperatures were closer to normal, but rarely exceeded 90 degrees in the northern two-thirds of the state through most of July. The coolest place in the state last month was Stockton in Jo Daviess County with an average temperature of 70.5 degrees, and the warmest place in the state in July was Cahokia with an average temperature of 79.8 degrees.
Overall, the preliminary statewide average July temperature was 75.3 degrees, 0.1 degrees below the 1991–2020 average and tied for 64th warmest on record going back to 1895.
Extreme Heat in Late July
July is the climatologically warmest month of the year in Illinois and typically has the highest frequency of extremely warm weather. The heat in Illinois in the last few days of July, though, was unusual, even for our hottest month. Daily high temperatures on July 27 and 28 exceeded 90 degrees across the state and topped 100 degrees in parts of western Illinois (Figure 3). Combined with extremely high humidity, heat index values pushed well over 100 degrees and even exceeded 110 to 115 degrees in some parts of central Illinois. Champaign reached a heat index of 115 degrees and Decatur had an incredibly dangerous 120-degree heat index on the afternoon of July 27. The latter number is only the third day on record with a 120+ degree heat index in Decatur and the first day since 1999.
The maps in Figure 3 show that low temperatures overnight on July 27–28 only dipped into the mid-70s across much of the state, and a few places had nighttime lows at or above 80 degrees. The combination of very high temperatures–day and night–and relentless humidity presented extremely dangerous weather for humans and animals. Heat remains the deadliest weather hazard in the United States, but still doesn’t get as much attention as more visibly noteworthy hazards such as tornadoes and winter storms. Imagine if there were a community of “heat-chasers” who were equally passionate about documenting and warning of the impact of heat as storm chasers are for their hazards. Outside of health impacts, the heat buckled roads in central Illinois, forced the cancellation of many outdoor events and practices, and even forced a famed root beer stand in Peoria–one frequented by a certain State Climatologist–to temporarily shut down to protect workers. The heat also came at a busy time for farm workers, who remain one of the most vulnerable groups to heat-related health impacts in Illinois.
Climate change has increased the frequency and intensity of hazardous heat conditions in Illinois, as in much of the United States. Figure 4 shows summer average maximum and minimum temperatures in Cook County between 1895 and 2022, with black lines showing 30-year trends over the long-term record. The plots show nighttime minimum temperatures have been consistently warming over the 125+-year record in Cook County, and daytime maximum temperatures have been increasing consistently since the early 1950s. Both daytime and nighttime temperatures are important for human and environmental health impacts from heat. Recent increases and projected continued increases in both summer maximum and minimum temperatures increase exposure risk to extreme heat across Illinois.
Some Drought Improvement with July Rainfall
The period from April to June this year was the sixth driest on record statewide, and a top five driest on record in a handful of counties in Illinois. Moderate to extreme drought covered most of the state coming into July, and there were serious concerns of agricultural and hydrology impacts from the drought. July weather was somewhat to much wetter than the previous three months because of an active storm track coming over the ever-persistent ridge in the southwest U.S.
July precipitation ranged from around 2 inches in western Illinois to over 10 inches in parts of southern Illinois. The southern and northeastern parts of the state were 2 to 6 inches wetter than normal last month because of very heavy precipitation events that are detailed below. Meanwhile, much of central Illinois was within 1 inch of normal and western Illinois was somewhat drier than normal (Figure 5). Last month was the wettest July on record at Chicago’s Midway airport, following what was the fourth driest April to June on record there.
The preliminary statewide total July precipitation 5.08 inches, 1.02 inches above the 1991–2020 average and the 22nd wettest on record.
Heavy Rain in Chicagoland & Southern Illinois
Meteorologists often quip that drought rarely breaks easily, referring to the alleged tendency for a drought to precede very heavy rainfall. The prolonged dryness in May and June in the Chicagoland area was indeed broken by a very intense rainfall event from a series of thunderstorms on July 1 and 2 (Figure 6). Among the highest 24-hour rainfall totals included 8.12 inches in Garfield Park, 8.6 inches in Cicero, and 8.96 inches in Berwyn. Based on the State Water Survey’s Bulletin 75 estimates, the event exceeded the estimated 1% annual exceedance probability storm (i.e., the 100-year storm*) in a few places. The heavy rain inundated stormwater systems and caused widespread flooding across the city, with thousands reporting flooded basements in Chicago alone.
*Two important caveats: 1) the “100-year storm” has a 1% chance of happening any given year, not once every 100 years, and 2) research has shown storm totals are increasing across Illinois, with a significant contribution from climate change.
Never to be outdone, southern Illinois decided to get in on the heavy rain action and experienced an incredibly intense series of training storms on July 18 and 19. Parts of Williamson, Johnson, Pope, Alexander, and Pulaski counties picked up over 8 inches of rain in less than 24 hours, with rainfall rates exceeding 3 inches per hour. Flash flooding occurred across the region, including at the Massac County Youth Fair (Figure 7). The event brought even more rain to western Kentucky and may have broken the Kentucky state record 24-hour rainfall total, with a preliminary 12.76 inches measured in Graves County. The measurement will need to be validated by a records committee before becoming official.
July Gave Out Free Smoke
As wildfires continued to burn across Canada in July, the Midwest ephemerally suffered from poor air quality as a result. While not quite as intense as in late June, much of northern and central Illinois experienced multiple days of unhealthy air quality last month. Figure 8 shows the number of poor air quality days (EPA Air Quality Index > 100) in Bloomington-Normal each year through July 31. Past drought years like 2012 and 2005 stick out with relatively frequent poor air quality days. However, the primary pollutant in these years was surface ozone, which is created effectively at very high temperatures that often correspond with drought. This year our high surface ozone levels have been augmented by high particulate matter from Canadian wildfire smoke.
As with extreme heat, health impacts from poor air quality are felt largely by folks most vulnerable to environmental hazards, including those experiencing homelessness or housing insecurity, those with strenuous outdoor jobs, and those with chronic respiratory and pulmonary illnesses such as asthma and COPD. The complicated territory and sheer size of the fires in Canada hinder their management, so it is likely the Midwest will continue experiencing on-again off-again poor air quality days in the coming weeks as long as the fires keep burning.
Late June Derecho
The switch from a dry June to wet and active July happened on June 29. That day, several rounds of severe storms moved through central and southern Illinois, producing large hail and a few tornadoes. The most destructive impacts from the storm, though, came from the derecho it produced: https://www.weather.gov/ilx/june29_derecho. A derecho is a widespread, long-lived windstorm that is associated with a series of strong thunderstorms. Most derecho impacts come from its incredibly strong straight-line winds. The June 29 event produced widespread 70–80 mph wind gusts from the Quad Cities to Danville, including one personal weather station in Taylorville that measured 101 mph wind.
The derecho caused substantial damage to trees, homes, and buildings, and caused widespread power outages. Perhaps some of the worst storm damage was in Springfield, which had an estimated $20 million in damages alone (Figure 9). The derecho caused significant crop damage across central Illinois, although not nearly to the extent of the infamous 2020 derecho that moved across Iowa, Illinois, and Indiana. This year’s derecho happened earlier in the growing season when corn was shorter and less brittle, and thankfully, it was much weaker than the 2020 event.
Speaking of Severe Weather…
No matter if we’re in Cairo, Egypt or Cairo, Illinois, drought is caused by a lack of precipitation over a period sufficiently long as to cause impacts. Because the same storms that bring severe weather also account for a big chunk of our warm season precipitation, summer drought years also tend to have a dearth of tornadoes, hail, and storm winds, but not this year. As of July 31, Illinois has had 125 tornadoes in 2023 reported by the Storm Prediction Center. Importantly, this is a preliminary total and may be adjusted later this year as reports are refined. However, if that total is accurate, it would give this year the third highest tornado frequency on record for any year (Figure 10). The current annual tornado record for Illinois is 142 in 2006.
August is the beginning of the end of summer but can certainly bring its fair share of heat. August is also an important month for finishing crops as we move toward fall. The most recent Climate Prediction Center outlooks for August show equal chances of above and below normal temperatures in much of the state, with higher odds of above normal temperatures in the southeast U.S. (Figure 11). Precipitation outlooks are leaning wetter than normal for much of the state, which would help continue the march out of drought in Illinois.
The bottom row in Figure 11 shows temperature and precipitation outlooks for the climatological fall season, September–November. The outlooks are decidedly equivocal, with equal chances of warmer, cooler, wetter, and drier than normal conditions in fall. It’s important to note that August to October is the “heart” of tropical storm season in the Atlantic, but the monthly and seasonal outlooks for the Midwest do not include any prediction of tropical storm frequency.