A Bit of Everything to Start Summer

June took a page out of March’s playbook—came in like a lamb and went out like a lion. Overall, the preliminary statewide average June temperature was 73.8 degrees, 1.6 degrees above the 1991–2020 average and tied for the 25th warmest on record going back to 1895. The preliminary statewide average total June precipitation was 5.33 inches, 0.68 inches above the 1991–2020 average and tied for the 30th wettest on record going back to 1895.  

Data are provisional and may change slightly over time

Hot Start, Cooler End to June

Drier soils in the northern two-thirds of the state helped elevate temperatures in the first half of June. Figure 1 shows daily temperature departures and daily average temperature this past month in Joliet. Most of northern and central Illinois experienced temperatures that were between 5 and 15 degrees warmer than normal in the first half of June. Rockford recorded 13 days with a high temperature at or above 90 degrees,  the fourth most for any June on record there back to 1893.

Figure 1. Daily temperatures in Joliet (black line) and daily temperature departures from the 1991 to 2020 normals (red and blue bars).

While northern Illinois stayed hot and dry in the first two weeks of June, temperatures in southern Illinois remained near to slightly cooler than normal (Figure 2). Temperatures in the latter half of the month were within 1 degree of normal north of Interstate 64, and between 1 and 2 degrees above normal in southern Illinois.

Figure 2. Average temperature departures between (left) June 1 and 15 and (right) June 16 and 30. Departures are from the 1991–2020 normal.

The warm start to June broke 31 daily high maximum temperature records and 15 daily high minimum temperature records. The subsequent cooldown in the third week of June broke 12 daily low minimum temperature records across the state.


Following a slow start to the growing season from cooler April and May weather, June temperatures helped accumulate growing degree days (GDD). The maps below in Figure 3 show total GDD accumulation and departures from the 1991–2020 normal since April 1. As of the start of July, growing degree day accumulation is ahead of normal in northern Illinois and slightly to much below normal in southern Illinois.

Figure 3. Maps show total base 50-degree modified growing degree day accumulation (left) and growing degree day departures from the 1991–2020 normal (right) since April 1.

Overall, June average temperatures ranged from the low 70s in northern and central Illinois to the mid- to high-70s in southern Illinois, between 1 and 5 degrees warmer than normal across the state (Figure 4). The preliminary statewide average June temperature was 73.8 degrees, 1.6 degrees above the 1991–2020 average and tied for 25th warmest on record going back to 1895.

Figure 4. June average temperature (left) and departure from the 1981-2010 normal (right).

Wild End to Otherwise Dry June

The first two-thirds of June was very dry across Illinois (Figure 5). In fact, the period between June 1 and 20 was the sixth and seventh driest on record in the northwest and northeast Illinois climate divisions, respectively. As the large atmospheric ridge established over the Pacific Northwest, most of Illinois found itself on the edge of a stationary front that produced several rounds of heavy rain from the St. Louis Metro East to Chicagoland. Due to the very wet last 7 to 10 days of the month, June ended wetter than average in all but the northwest and southwest climate divisions, and it was the sixth wettest on record in the east-central division.

Figure 5. Climate division rankings of total precipitation from (left) June 1 through the 20, and (right) the entire month of June. Lower values indicate wetter conditions. Data source: Iowa Environmental Mesonet.

Rain in the final week of June was particularly heavy along the Interstate 55 corridor between Bloomington-Normal and Chicago. Areas of McLean and Livingston Counties observed 8 to 10 inches of rain in just 4 days (Figure 6), resulting in serious flooding in Bloomington, flooding on and the temporary shutdown of Interstates 55 and 74, and standing water in fields across central and northeast Illinois.


CoCoRaHS observers in both south Bloomington and Heyworth in McLean County observed over 10 inches of rain in just 3 days between June 25 and 27. According to the recently published Bulletin 75, these totals exceeded the 1% annual probability or “100-year” rainfall event by 1.5 inches.

Figure 6. Total precipitation at weather stations across central Illinois between June 25 and 28. Source: National Weather Service, Lincoln, IL.

Total June rainfall ranged from less than 3 inches in far northwest and southeast Illinois to over 12 inches in central and east-central Illinois (Figure 7). Most areas between the St. Louis Metro East and Chicago areas were between 1 to 5 inches wetter than normal, while southern and northwest Illinois were 1 to 3 inches drier than normal. Overall, the preliminary statewide average total June precipitation was 5.33 inches, 0.68 inches above the 1991–2020 average and tied for the 30th wettest on record going back to 1895.

Figure 7. Maps show (left) total June precipitation and (right) total June precipitation departure from 1991–2020 normal.

Drought Continues in Northern Illinois

The dry, hot start to June culminated in the U.S. Drought Monitor introducing extreme drought in northeast Illinois in mid-June in response to very dry soils, low streamflow in major streams, and increasingly concerning crop stress. Persistent heavy rains in the Chicagoland area in late June were crucial to improving drought conditions and alleviating crop and water stress across the region. The most recent (July 1) edition of the U.S. Drought Monitor showed most of the southern and central Chicagoland metro area remained abnormally dry to near normal, which represented a significant improvement since mid-month (Figure 8). However, areas north of Interstate 88 and west of Interstate 39 did not receive as much rain in the final week of June, and drought conditions have worsened, particularly from Winnebago to Jo Daviess Counties. In fact, June was the fifth driest on record in Stockton in Jo Daviess County back to 1944, and the driest since 2012.

Figure 8. U.S. Drought Monitor map, updated through June 29.

We will continue to monitor evolving conditions across Illinois and hope to see continued improvement in hydrology and ecology throughout northeast Illinois. Concurrently, the northwest corner continues to deteriorate as precipitation deficits increase. July is the climatologically warmest month in Illinois, and high temperatures can intensify dry conditions. Therefore, the northwest corner of the state will need near to above normal rainfall in July to curb worsening drought conditions.

Outlooks

We’re in a bit of a transition in weather patterns to start July. Climate Prediction Center outlooks for the second week of the month show elevated odds of warmer and wetter than normal conditions statewide (Figure 9). Meanwhile, longer-term outlooks for the entire month of July do not show much of a strong signal in either temperature or precipitation (Figure 10). Illinois appears to be on a boundary between warm, dry conditions to our north and northwest and cooler, wetter conditions to our south and southeast. Climate prediction more than two weeks out in the summer is very difficult here in the Midwest, so we will have to see how shorter-term outlooks and forecasts evolve as we move deeper into the summer.

Figure 9. Climate Prediction Center Outlooks of (left) temperature and (right) precipitation for the second week of July.
Figure 10. Climate Prediction Center Outlooks of (left) temperature and (right) precipitation for the entire month of July.

Update to Northern Illinois Drought

A warm and dry first half of June has persisted or worsened drought conditions in northern Illinois. Here is an update of current conditions and a look ahead into this summer.

U.S. Drought Monitor

The latest version of the National Drought Mitigation Center’s U.S. Drought Monitor, which was current as of June 15th, showed an expansion of both moderate drought (D1) and severe drought (D2) across northern Illinois. The Drought Monitor also introduced extreme drought (D3) in all or parts of Lake, McHenry, Boone, DeKalb, Kane, and Cook Counties in northeast Illinois as well as in parts of southern Wisconsin. The last time the Drought Monitor showed extreme drought in any part of Illinois was October 2012. Currently, over 9% of the state is in at least moderate drought, over 6% of the state is suffering from severe drought, and nearly 3% of the state is now in extreme drought according to the U.S. Drought Monitor.

U.S. Drought Monitor for Illinois, current as of June 15th.

Precipitation Deficits

May wrapped up an extremely dry spring. The period March to May this year was the 3rd driest spring on record in Chicago and the driest since 1934. The maps below show spring precipitation in northern Illinois was 2 to 6 inches below the 1991-2020 normal, with the largest deficits in far northeast Illinois.

Figure 2. Maps show (left) total precipitation, (middle) total precipitation departure from 1991-2020 normal, and (right) total precipitation as a percent of the 1991-2020 normal for (top maps) climatological Spring and (bottom maps) June to date. Map source: Midwestern Regional Climate Center (https://mrcc.illinois.edu).

The dry weather pattern continued throughout the first half of June. The northern half of the state received between 0.5 inches and 2.5 inches below normal precipitation in the first half of June, between 10% and 50% of the 1991-2020 normal. The combination of spring and the first half of June has left northeast Illinois with an 8 to 10 inch precipitation deficit since March 1st, and northwest Illinois with a 4 to 6 inch precipitation deficit since March 1st (Figure 3).

Figure 3. Precipitation between March 1st and June 15th expressed as departures from 1951 to 2020 average. Data source: Iowa Environmental Mesonet (https://mesonet.agron.iastate.edu/).

June Heat Not Helping

Extensive precipitation deficits have left parched soils and reduced flow in both small and large streams throughout northern Illinois. These impacts have been exacerbated by the extreme high temperatures in the region during the first half of June. Average temperatures in northern Illinois between June 1st and June 15th were between 6 and 10 degrees above the 1991 to 2020 normal. The first half of June was the warmest on record in Chicago and the third warmest on record in both Rockford and Moline; all three of these stations’ records stretch back to the 1870s. Very warm weather has increased evaporative demand on already dry soils and stressed vegetation and crops, worsening the drought conditions and associated agriculture, water resource, and ecological impacts.

Figure 4. Left map shows average temperature between June 1st and June 15th expressed as departures from 1991 to 2020 normal. Right map shows June 1st to June 15th average temperature expressed as a climatological ranking, with 1 representing the warmest on record at that station.

Impacts So Far

The timing of this drought is different than the “droughts of record” of 1988 and 2012 such that the “peak” of those past droughts was later in the summer in July and August. The relatively early onset of this year’s drought has likely limited impacts to agriculture, water resources, and ecosystems so far. However, reports of impacts to crops in northern Illinois include corn plants curling leaves, early firing, and stunted growth in both corn and soybeans. Gardeners and horticulturalists across northern Illinois report having to water gardens and specialty crops much more frequently, and lawns, trees, and shrubs are reportedly showing significant drought stress in residential areas. 

Outlook

The June 17th National Weather Service precipitation forecast indicates the potential for widespread 1 to 2 inches accumulation across northern Illinois over the 7 days. It is understandable if folks are skeptical of the forecast, given how frequently wet forecasts have not come to fruition in northern Illinois over the past three months; however, this is the best chance for drought alleviation since mid-May. If the forecast does verify it will not eliminate drought in northern Illinois but will go a long way to improve soil moisture and reduce stress in crops and ecosystems.

Figure 5. National Weather Service 7-day precipitation forecast issued on June 17th.

Meanwhile, Climate Prediction Center outlooks indicate a tendency for cooler and wetter than normal conditions statewide in the third week of June. Both outlooks are potentially good news for drought affected areas, and we could see real improvement with soaking rains combined with below average evaporative demand from the cooler weather. However, many more weeks of wetter weather are needed to ameliorate drought in northern Illinois and stave off further impacts as we move into the heart of summer. 

Figure 6. Temperature (left) and precipitation (right) outlooks from the Climate Prediction Center for the third week of June.

Drought Continues in Northern Illinois

As the western U.S. fights record drought conditions, northern Illinois has endured a significant dry spell of its own. Here is an update of current conditions and a look ahead into this summer.

U.S. Drought Monitor

The latest version of the National Drought Mitigation Center’s U.S. Drought Monitor, which was current as of June 1st, showed an expansion of both moderate drought (D1) and severe drought (D2) across northern Illinois. Currently, nearly 6% of the state is in at least moderate drought and over 4% of the state is suffering from severe drought, according to the U.S. Drought Monitor.

Figure 1. U.S. Drought Monitor map of drought conditions in Illinois, current as of June 1st, 2021.

Precipitation Deficits

May was unusually dry across much of northern Illinois, with the largest deficits of 2 to 3 inches below the 1991 to 2020 average in northeast Illinois. May followed very dry months in March and April, and climatological spring precipitation ranged from 25% to 60% of the 1991 to 2020 average in northeast Illinois.

Figure 2. Maps show (left) total precipitation, (middle) total precipitation departure from 1991-2020 normal, and (right) total precipitation as a percent of the 1991-2020 normal for (top maps) May and (bottom maps) climatological Spring, which is from March through May.

This spring ended as the third driest on record in Chicago (back to 1871) and the driest since 1934 with only 3.75 inches of total precipitation between March and May (Figure 3). For reference, the long-term average spring precipitation total in Chicago is 9.36 inches. Incredibly, this extremely dry spring followed the very wet springs of 2019 and 2020, which were the 2nd and 3rd wettest on record in Chicago.

Figure 3. Total spring (March – May) precipitation in Chicago from 1871 to present.

Soil Moisture Conditions

Soil moisture is depleted across northern Illinois in response to the lack of spring precipitation. The plots below show current soil moisture conditions at Illinois Climate Network stations in Freeport (Stephenson County), DeKalb (DeKalb County), and St. Charles (Kane County). Current soil moisture is shown in the blue line and depicted in volumetric water content units (m3/m3). In the background of each of these plots is the soil moisture climatology at each of these stations to better understand the climatological context of current soil moisture. Soil moisture at 4 inch and 8 inch depths are near or below the climatological 10th percentile at all three locations. Soil moisture at 4 inch depth at both Freeport and St. Charles is approaching a value of 0.20 or approximately 20% moisture by volume, which is close to the permanent wilting point of these soils. Once soils dry to or beyond the permanent wilting point, plants are unable to effectively extract water out of the soil, and we typically see impacts to crops and natural ecosystems as soil moisture approaches the wilting point. Importantly, deeper layer soil moisture at 20 inch depth is still abundant at both Freeport and DeKalb. This deeper layer moisture tends to be less affected by short-term drought and is more reflective of climate conditions at 6 to 18 month periods. The abundant deeper layer moisture at Freeport and DeKalb can help alleviate significant moisture stress for established trees and shrubs; however, the relatively more severe drought conditions in northeast Illinois has left 20 inch soil moisture more depleted at St. Charles.

Figure 3. Soil moisture conditions at Illinois Climate Network stations in Freeport, DeKalb, and St. Charles. Current soil moisture at 4 inch, 8 inch, and 20 inch depths are shown in the blue line, in the context of the soil moisture climatology at each station.

A Look Ahead

Unfortunately, the near-term forecasted weather is not conducive for alleviation of drought conditions in northern Illinois this upcoming week. Temperatures are forecasted to reach into the high 80s and low 90s across northern Illinois this weekend and throughout next week. High temperatures will increase evaporative demand and evaporation from already moisture-stress soil and plants, exacerbating ongoing drought impacts to agriculture and ecosystems.

Meanwhile, National Weather Service precipitation forecasts (below) call for mostly less than half an inch of rain over the next 7-days across northern Illinois. The combination of very high temperatures and evaporation with little to no rain will likely degrade dry conditions and heighten drought impacts across northern Illinois this upcoming week.   

Figure 4. National Weather Service 7-day precipitation forecast for the period June 3rd through June 10th.

Outlooks from the Climate Prediction Center for week 2, the period June 10th through June 16th, are also showing highest probabilities of warmer and drier than normal conditions across the state. Given the current conditions and predictions for the next two weeks, it is very unlikely drought will be alleviated in northern Illinois in the first half of June.

Figure 5. Climate Prediction Center (left) temperature and (right) precipitation outlooks for June 10th through June 16th, showing highest odds of warmer and drier than normal conditions across northern Illinois.

May Brought a Cool End to Spring

This past month is quite challenging to summarize across the state. Overall, the preliminary statewide average May temperature was 60.8 degrees, 2.5 degrees below the 1991–2020 average and tied for 42nd coldest on record going back to 1895. The preliminary statewide average total May precipitation was 4.50 inches, 0.26 inches below the 1991–2020 average and tied for the 50th wettest on record going back to 1895.  

Data are provisional and may change slightly over time

May Continued Spring Temperature Rollercoaster

May temperatures varied substantially as the daily temperature departures from Aurora show below (Figure 1). Average temperatures ranged between 5 and 15 degrees below normal for all but a handful of days in the first half of the May, followed by a 10-day period of average temperatures 5 to 15 degrees above normal. Temperatures dropped in the last week of May as a cold front moved through the Midwest ahead of the Memorial Day weekend.

Figure 1. Daily temperatures in Aurora (black line) and daily temperature departures from the 1991-2020 normal (red and blue bars).

The temperature swings broke 10 daily high maximum temperature records, 39 daily high minimum temperature records, 14 daily low maximum temperature records, and 33 daily low minimum temperature records.

May average temperatures ranged from the high 50s in northern Illinois to the mid-60s in southern Illinois, between 1 and 3 degrees colder than normal in all but northern Illinois.

Figure 2. May average temperature (left) and departure from the 1981-2010 normal (right).

May temperatures kept growing degree accumulation below normal across the state. Base 50-degree modified growing degree day accumulation in May ranged from over 450 in southern Illinois to around 400 in northern Illinois. May growing degree day accumulation was between 10 and 60 below the 1991-2020 average across the state, with the largest departures in southern Illinois (Figure 3).  

Figure 3. Maps show May total base 50-degree modified growing degree day accumulation (left) and growing degree day departures from the 1991-2020 normal (right).

Overall, the preliminary statewide average May temperature was 60.8 degrees, 2.5 degrees below the 1991–2020 average and tied for 42nd coldest on record going back to 1895.

Average spring temperatures ranged from the high 40s in northern Illinois to the mid-50s in southern Illinois, between 2 and 3 degrees warmer than the 1991-2020 normal in northern Illinois and within 1 degree of normal in central and southern Illinois. Spring 2021 was the 6th warmest on record in Rockford (record back to 1893) and the warmest spring since 2012.

Figure 4. Maps show spring (March to May) average temperature and departure from 1991 to 2020 normal.

Wet West, Dry Elsewhere in May

May precipitation was highly variable across Illinois. Monthly totals ranged from over 6 inches in western Illinois to less than 2 inches in far northern Illinois. These totals represent from a 2- to 3-inch surplus in western Illinois to 2- to 3-inch deficits in southwest and northeast Illinois, relative to the 1991-2020 normal.

Overall, the preliminary statewide average total May precipitation was 4.50 inches, 0.26 inches below the 1991–2020 average and tied for the 50th wettest on record going back to 1895.  

Figure 5. Maps show (left) total May precipitation and (right) total May precipitation departure from 1991-2020 normal.

Spring Drought Continues in Northern Illinois

May marked the fourth consecutive month of below average precipitation in northeast Illinois. The maps below show total precipitation as a departure from the 1991-2020 normals for March, April, and May and the climatological spring. Through each of the three spring months, the northeast corner of the state experienced well below normal precipitation, culminating in a 6- to 7-inch precipitation deficit in northeast Illinois since March 1.   

Figure 6. Maps show March, April, and May and climatological spring (March – May) total precipitation as a departure from the 1991 to 2020 normal.

This spring ended as the third driest on record in Chicago (back to 1871) and the driest since 1934 with only 3.75 inches of total precipitation between March and May (Figure 7). For reference, the long-term average spring precipitation total in Chicago is 9.36 inches. Incredibly, this extremely dry spring followed the very wet springs of 2019 and 2020, which were the 2nd and 3rd wettest on record in Chicago.

Figure 7. Total spring (March – May) precipitation in Chicago from 1871 to present.

Outlooks

Summer is notoriously challenging for skillful seasonal climate prediction because of the lack of influence of large-scale patterns like the El Niño-Southern Oscillation (ENSO) on summer climate in the central U.S. The most recent 1-month and 3-month outlooks from the Climate Prediction Center reflect the relatively low confidence in summer climate prediction. Both the outlooks for June and those for climatological summer (June – August) show mostly equal chances of above normal, normal, and below normal temperature and precipitation across the state.

Without large-scale atmospheric conditions that are conducive to wetter weather in northern Illinois, amelioration of drought conditions will depend mostly on small-scale thunderstorms and precipitation from tropical systems, both of which are very difficult to forecast more than a few days ahead. Therefore, the Climate Prediction Center drought outlook shows drought in northern Illinois persisting through the month of June.

Figure 8. Climate Prediction Center Outlooks of (left) temperature and (right) precipitation for (top) June and (bottom) June – August.