| Illinois experiences distinct seasonal weather patterns throughout the year. January and February are typically the coldest and driest months, with average high temperatures below freezing and snowfall common. Spring (March-May) brings a transition with rising temperatures and increasing precipitation, with May and June being the wettest months. Summers (June-August) are warm and humid, with July often being the hottest month. Fall (September-November) features a gradual cooling trend with some periods of pleasant, sunny weather and decreasing precipitation. Winter (December-February):December: Temperatures start to drop, with average highs around 37°F (2.7°C) and lows around 22°F (-5.5°C). Snowfall is likely, especially later in the month. January: The coldest month, with average high temperatures around 26°F (-3.3°C) and lows around 11°F (-12°C). Snowfall is common, and wind chill can make it feel much colder. February: Temperatures begin to rise slightly, with average highs around 31°F (-0.5°C) and lows around 15°F (-9.4°C). Snowfall is still likely, but there's a chance of some milder days.

Spring (March-May):March: Temperatures start to climb, with average highs around 41°F (5°C) and lows around 26°F (-3°C). Snowfall may still occur early in the month, but the weather will become increasingly milder and wetter. April: Temperatures continue to rise, with average highs around 52°F (11.1°C) and lows around 37°F (2.7°C). Precipitation increases, with more rain than snow. May: Temperatures are mild, with average highs around 64°F (17.7°C) and lows around 47°F (8.3°C). This is one of the wettest months, with frequent rain showers.

Summer (June-August):June: Temperatures continue to rise, with average highs around 76°F (24.4°C) and lows around 57°F (13.9°C). It's still relatively wet, with June being another one of the wettest months. July: The hottest month, with average highs around 84°F (28.9°C) and lows around 63°F (17.2°C). Humidity is often high, and there's a chance of thunderstorms. August: Temperatures remain warm, with average highs around 81°F (27.3°C) and lows around 61°F (16.3°C). It's still relatively humid, but there's a gradual decrease in rainfall compared to June and July.

Fall (September-November):September: Temperatures start to cool down, with average highs around 76°F (24°C) and lows around 54°F (12°C). Rainfall decreases, and the weather can be pleasant with sunny days. October: Temperatures continue to drop, with average highs around 63°F (17.2°C) and lows around 42°F (5.6°C). Snowfall is possible later in the month, especially in northern Illinois. November: Temperatures are cold, with average highs around 45°F (7.2°C) and lows around 29°F (-1.7°C). Snowfall is common, and the winter weather begins to set in.
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