Illinois Climate
Top 5 Cities: Chicago, Aurora, Rockford, Joliet, and Naperville
This month in numbers
April 2026 was Illinois's warmest April on record, with an average temperature of 14.89°C, an anomaly of +3.8°C above the 1961–1990 baseline. This marks the 1st warmest April in 77 years of records. Maximum temperatures also ranked high, coming in as the 3rd warmest April on record at 21.11°C, also +3.8°C above average. Globally, April 2026 was the 2nd warmest April on record for land temperatures.
What changed
Looking at the broader picture, the February–April 2026 period was the 3rd warmest on record for Illinois, with an average temperature of 8.5°C, a significant +4°C above the long-term average. Maximum temperatures for this three-month period were even more striking, ranking as the 2nd warmest on record at 14.89°C, an anomaly of +4.8°C. This warming trend in Illinois aligns with a broader pattern across the US, as 9 of the top 10 warmest regions for the 3-month anomaly were US states.
What’s driving change?
The pronounced warming in Illinois is consistent with the broader trend of land warming faster than the ocean. Illinois has also experienced significant extreme weather events recently. April saw multiple severe storm systems, including a major tornado outbreak between April 17–18, which produced over two dozen tornadoes across central Illinois, causing structural damage and exacerbating river flooding. Another severe weather event on April 27 brought widespread wind damage and five EF1 tornadoes, along with flash flooding. While drought conditions have been a concern, substantial rainfall in March and April has largely alleviated them across central and southeast Illinois. However, there have been three wildfire events and two drought events logged for Illinois over the past 12 months, with the recent occurrences representing 100% of the annual total for both types, indicating an unusual concentration of these events. You can track active extreme weather events at Extreme Weather tracker.
Looking ahead
Official outlooks from NOAA's Climate Prediction Center favour below normal temperatures for central Illinois during May 2026, with equal chances of above or below normal precipitation.
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.