Illinois Climate – July 2026 Update
Top 5 Cities: Chicago, Aurora, Rockford, Joliet, and Naperville
Summary
July 2026 across Illinois combined oppressive heatwaves, severe thunderstorm outbreaks, and air quality advisories from wildfire smoke. While state temperatures averaged slightly above baseline, a prominent high-pressure system drove heat indices past 38°C early in the period, followed by severe storms causing local flash flooding. Globally, land temperatures reached historic levels, with the month ranking 3rd warmest on record. Looking ahead, outlooks suggest warm conditions will persist through late summer into autumn.
This month in numbers
Illinois recorded an average temperature of 24.89°C during July 2026, sitting 0.8°C above the 1961-1990 baseline and ranking as the 21st warmest such month in 77 years of records. Maximum temperatures averaged 30.39°C, which was 0.2°C above baseline and ranked 29th highest. Total precipitation reached 85.09 mm, falling 18.1 mm below the long-term average to rank 50th. In global context, land temperatures soared to 15.8°C, marking the 3rd warmest July on record worldwide at 1.6°C above baseline, while the May-July global land average of 14.34°C ranked 2nd warmest ever.
What changed
Taking a broader three-month perspective, May-July 2026 delivered an average temperature of 21.32°C across Illinois, running 0.4°C above baseline and ranking 31st warmest on record. Cumulative rainfall over the same period reached 336.8 mm, which was 31.2 mm above normal and ranked 36th wettest. Regionally, Illinois tracked cooler than the wider United States, which posted a monthly anomaly of +1.5°C above average. Within its NOAA Ohio Valley regional group, where member anomalies averaged +1.14°C, Illinois sat 0.30°C below the group average, trailing warmer neighbouring states such as West Virginia and Ohio. Readers can explore regional comparisons at US Ohio Valley.
What’s driving change?
The elevated temperatures early in the month were amplified by atmospheric , which trapped warm air and pushed localised heat indices above 38°C. Subsequent allowed cooler air masses and severe weather fronts to cross the region, triggering intense downpours that overwhelmed urban drainage systems. effects further prevented night-time cooling in major metro areas. On a wider scale, all of Illinois's 1 tropical cyclone this year happened in the past month, tracked on our live map at Extreme Weather tracker.
Looking ahead
Seasonal forecasts from NOAA's Climate Prediction Center indicate a higher probability of above-average temperatures across Illinois through late summer and into autumn, accompanied by equal chances of above or below-normal precipitation.
Generated by Gemini from climate data and web sources
At a Glance
Temperature – Average
Climate Map – USUnited States
Source: NOAA Climate at a Glance — US states & climate regions (tavg, pcp), plus GPCC (Snow, water-equivalent). Anomalies are vs the 1961–1990 baseline. See methodology.
Typical Climate – Illinois
Köppen Dfa · ContinentalIllinois has a continental climate (Köppen Dfa: Humid continental - hot summer), with distinct warm summers and cool-to-cold winters. July is typically the warmest month, averaging 24.4°C, while January is the coldest at -2.5°C. Annual precipitation averages around 1021mm, spread fairly evenly across the year.
Monthly climate normals (2016–2025) - bar colour and height show average temperature, the shaded area shows average monthly rain, with snow (water-equivalent) shown separately.
Data: NOAA National Centers for Environmental Information (temperature/precipitation; frost: World Bank CCKP; snow: GPCC (DWD)).
Long-Term Trends
Combined Timeline – Illinois
Precipitation, Sunshine, Frost and Snow are converted to standard deviations from their own average so they can share an axis with Temperature.
Data: NOAA National Centers for Environmental Information (temperature/precipitation; frost: World Bank CCKP; snow: GPCC (DWD)).
Heatwave Days – Illinois
Warm Spell Duration Index (WSDI) - days in a 6+ day run above the local 90th-percentile temperature for that time of year.
Data: World Bank Climate Change Knowledge Portal (ERA5-derived). Refreshed roughly 1-2x/year, ~7-8 months behind present.
Year-on-Year Trends
The 4byo Climate Helix – Illinois
Data: NOAA National Centers for Environmental Information (temperature/precipitation; frost: World Bank CCKP; snow: GPCC (DWD)).
Monthly Temperature – Illinois
Background lines show the last 40 years (plus the record year and its opposite, wherever they fall).
Data: NOAA National Centers for Environmental Information (temperature/precipitation; frost: World Bank CCKP; snow: GPCC (DWD)).
Records – Illinois
NOAA National Centers for Environmental Information (frost: World Bank CCKP; snow: GPCC (DWD)) - Anomalies vs 1901-2000 mean
Shifting Seasons
Warm / cold seasonsKöppen Dfa · ContinentalHow spring and autumn have shifted in Illinois. Spring is defined as the date monthly temperatures first rise above the long-term annual mean (10.7°C, from 1950–1979); autumn is the date they fall back below it. Temperature swings 28.4°C peak-to-peak across the year - a classic four-seasons rhythm.
Baseline vs recent monthly temperature climatology. Biggest warming: Mar (+2.7°C).
Data: NOAA National Centers for Environmental Information (temperature/precipitation; frost: World Bank CCKP; snow: GPCC (DWD)).
Emissions & Energy
Explore
Explore Climate Data
Data Sources
Data Sources for Illinois
Every figure on this page is sourced from official, openly published climate datasets. Anomalies are calculated against the 1961–1990 baseline (temperature) and 1991–2020 (rainfall, sunshine, frost) - see the Methodology & Sources page for the complete dataset list and update calendar.
Statewide monthly temperature and precipitation (nClimDiv).
Frost Days and Heatwave Days (Warm Spell Duration Index), ERA5-derived. World Bank Climate Change Knowledge Portal.
Monthly snow water-equivalent, Global Precipitation Climatology Centre (DWD).
FAQs
FAQs
How is the climate in Illinois changing?
Illinois is warming in line with the rest of the world. The page above shows the latest monthly temperature anomaly versus the 1961-1990 baseline, the long-term annual trend, and the region's rank in the historical record. The headline panel also shows the long-term trend rate per decade and the warmest and coolest years on file.
What is the climate like in Illinois?
Illinois has a continental climate (Köppen Dfa: Humid continental - hot summer), with distinct warm summers and cool-to-cold winters. July is typically the warmest month, averaging 24.4°C, while January is the coldest at -2.5°C. Annual precipitation averages around 1021mm, spread fairly evenly across the year.
Where does the climate data for Illinois come from?
Climate data for Illinois comes from NOAA Climate at a Glance (temperature and precipitation), refreshed every month, when the upstream temperature and rainfall data are refreshed.
What is the climate baseline used on this page?
Anomalies on this page are calculated against the 1961-1990 climatological baseline, which is the standard reference period used by the Met Office, NOAA, IPCC and most national climate services. Some panels also show the source-native 1901-2000 (NOAA) or 1991-2020 (WMO) baselines for verification. See Methodology & Sources for the full reference.
Which areas does the Illinois climate data cover?
The Illinois climate profile covers Chicago, Aurora, Rockford, Joliet and surrounding areas. Illinois climate data from NOAA Climate at a Glance
How often is the Illinois climate update refreshed?
The Illinois climate update is refreshed monthly, typically a few days after the previous month closes and the upstream provider (Met Office HadUK-Grid, NOAA Climate at a Glance, Copernicus ERA5 or the Global Carbon Project) publishes its update. See the Climate Rankings for cross-region comparisons.
What counts as a Heatwave Day on the Illinois climate page?
Heatwave Days use the Warm Spell Duration Index (WSDI) - the WMO/ETCCDI-standard heatwave measure: days that are part of a run of 6 or more consecutive days above the local 90th-percentile temperature for that calendar day. The 90th-percentile threshold varies by time of year (a hot day in January is judged differently to one in July) but is fixed to the 1961-1990 baseline for every year shown - it does not shift as the climate warms, which is why Heatwave Days trend upward over time.
Does the Illinois climate page include frost and snow data?
Yes. Frost Days (days with a minimum temperature below 0°C, World Bank CCKP) and snow water-equivalent (GPCC) are shown alongside temperature and precipitation, each measured against the 1961-1990 baseline where a like-for-like historical comparison is available.