What Is the Weather Like in Illinois?

Tornado season is in full swing with the most dangerous period from April through mid-June. Severe thunderstorms can produce tornadoes, large hail, and damaging straight-line winds — have a storm shelter plan. Spring flooding is common as snowmelt combines with heavy rain, especially along the Mississippi, Missouri, and Ohio River systems. Temperatures yo-yo from the 40s into the 70s°F with dramatic swings week to week. Wildflowers emerge and farmers begin planting.

Hot and humid with temperatures in the 85–100°F range and the corn belt humidity making it feel even hotter. Severe thunderstorms remain a threat with derechos (long-lived damaging wind storms) possible. State fairs, barbecues, and lake recreation are summer staples. The region produces some of the most spectacular lightning displays in the country. Mosquito activity is heavy near standing water. Evening baseball, fireworks, and outdoor concerts thrive.

A beautiful season as the oppressive humidity breaks and temperatures ease into the 50s–70s°F. Harvest season transforms the landscape with golden cornfields and combines running at full speed. Fall foliage peaks from late September in Minnesota and Wisconsin through late October in Missouri and Kentucky. High school and college football dominate weekends. First frost arrives in September in the north and October further south. November brings the transition to winter with increasing gray skies.

Brutally cold with average highs in the 20s–30s°F and arctic outbreaks pushing wind chills to -20 to -40°F. Lake-effect snow belts near the Great Lakes can see 60–100+ inches of snow per season. Blizzards can produce whiteout conditions and paralyze travel for days. Ice fishing, snowmobiling, and cross-country skiing are popular winter activities. Keep an emergency kit in your vehicle — getting stranded in winter weather can be dangerous.