Chicago's summer severe weather season may be worse than usual in 2025
Summer is finally returning to Chicagoland as Lake Michigan beaches open and crowds return to farmers markets and street fairs.
But summer is also Chicago's wettest season, and the time of year when severe thunderstorms and tornadoes are most common. The First Alert Weather team is tracking two reasons why the 2025 severe storm season may be worse than normal.
Derechos, defined as widespread damaging wind events from a cluster of thunderstorms that produces 58+ mph winds and a swath of damage at least 240 miles long, happen on average once a year in any given city in Illinois. This makes our area among the most susceptible in the country to thunderstorm wind damage.
Derechos occur most frequently in the late spring and summer months, peaking from May through July.
Studies find that thunderstorm wind damage is happening more often as the climate warms, with one study concluding that "the central U.S. experienced a fivefold increase in the geographic area affected by damaging thunderstorm straight line winds in the past 40 years."
Illinois is also increasingly becoming a dangerous part of the U.S. for tornado outbreaks. Northern Illinois just had back-to-back record tornado years, with 58 tornadoes in 2023 and 63 in 2024. The long-term average in our area is 15-20 tornadoes per year, according to the National Weather Service Romeoville office.
Illinois as a whole also experienced a record-setting year for tornadoes in 2024 with 142 tornado touchdowns, beating the previous record of 124 tornadoes in 2006.
Ongoing research suggests that tornado alley is shifting from its traditional bullseye in the Plains eastward into the Deep South and Midwest. Tornadic storms appear to be happening more frequently in these areas as the dryline — a focus for severe storm development — shifts eastward as parts of Texas and Oklahoma become more arid. One-day tornado outbreaks are also getting bigger as the climate warms, and tornadoes are happening at less typical times of the year.
There are several factors that may influence how bad this severe weather season is in Illinois.
The ENSO cycle, which is the natural swing from El Niño to La Niña, is currently in a neutral phase, and is expected to remain so through the summer. While La Niña can mean more tornadoes in the central U.S., a neutral phase suggests a more typical year. Historic tornado outbreaks in 1974, 2008 and 2011 all came following La Niña conditions the previous winter, which is where we find ourselves this year.
A less-often discussed natural cycle called the Madden-Julian Oscillation (MJO) is also currently in a relatively neutral phase, not suggesting a short-term severe weather increase nor a decrease.
One possible factor that may slant Illinois toward a more active severe weather season in addition to trends observed with climate change is the Pacific-North America Pattern (PNA). One study found that a negative PNA pattern, which is occurring now, can lead to more significant tornado outbreaks in the central U.S..
Outlooks from the NOAA Climate Prediction Center are suggesting odds of a warmer than normal summer across Illinois with near-normal rainfall.
Without strong forcing one way or another from the long-term patterns discussed above, the Climate Prediction Center cites soil moisture as a dominant factor in temperatures this summer.
While we have enjoyed some much-needed rainfall across the state in the final week of May, central and northern Illinois still have very dry soil heading into the summer months, which favors hotter temperatures in the absence of more significant rain.
The overall warming climate will also impact Chicago's summer weather this year. Last year, 2024, was Chicago's warmest year on record, with records dating back more than 150 years.
Chicago summers have warmed by 1.7 degrees Fahrenheit just since 1990, and winters are warming twice as fast. While the urban heat island effect does lead to warmer temperatures in cities compared to nearby rural areas, cities and farmland are both warming at the same rate.
As the climate continues to warm, the U.S. Environmental Protection Agency warns of more heat-related deaths in northern Illinois due to higher heat and humidity, worse air quality and longer pollen seasons for allergy sufferers.
