Illinois Climate
Top 5 Cities: Chicago, Aurora, Rockford, Joliet, and Naperville
This month in numbers
March 2026 was exceptionally warm for Illinois, ranking as the 2nd warmest March in 77 years of records, with an average temperature of 9.22°C, a significant 4.7°C above the 1961–1990 baseline. Maximum temperatures also soared, reaching 16.17°C on average, making it the 2nd warmest March for maximum temperatures on record, an anomaly of +6.3°C. Globally, April 2026 also ranked as the 2nd warmest April for land temperatures, at 14.96°C, an anomaly of +1.1°C.
What changed
Over the past three months (January–March 2026), Illinois experienced an average temperature of 2.13°C, which is 2.9°C above the 1961–1990 baseline, placing it as the 12th warmest such period on record. For maximum temperatures, the state saw its 6th warmest January–March period, with an average of 8.09°C, an anomaly of +3.8°C. While temperatures have been notably high, precipitation for the same three-month period was below average, at 51.65 mm, a deficit of 6.5 mm. Illinois's 1-month temperature anomaly of +4.72°C places it 24th out of 234 regions globally, and it was the 5th warmest within its NOAA Ohio Valley US climate region group.
What’s driving change?
The pronounced warmth in Illinois during March, and the broader three-month period, can be attributed to several factors. A significant tornado outbreak occurred from March 10–12, 2026, across the Midwestern United States, including central and eastern Illinois, with unseasonably warm and humid air masses pushing temperatures into the upper 70s and lower 80s Fahrenheit, setting new record highs in some areas. This aligns with a broader trend of jet stream shifts, which can lead to stalled weather systems and prolonged periods of unusual warmth. The current ENSO state is Neutral, with a weekly Niño 3.4 SST anomaly of +0.9°C, but forecasts indicate a 61% chance of El Niño developing by May–July 2026, which typically brings warmer and drier conditions to Illinois. The state has also been grappling with ongoing drought conditions, with two drought events active as of early May, representing 100% of the annual total for Illinois, an unusual concentration for the region. This can exacerbate warming, as dry soils are less able to cool themselves through evaporation. Additionally, Illinois has experienced an unusual concentration of extreme weather events, including two drought events, one flood event, and one wildfire event in the past 12 months, all representing 100% of their respective annual totals for the state, as tracked on Extreme Weather tracker.
Sources:
Generated by Gemini from climate data and web sources
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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.
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 trend rate is shown as °C per decade in the headline panel; you can also see the warmest and coolest years on file.
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.