The hottest month in Illinois is July when the average maximum temperature is 29°, average temperature is 24° and average minimum temperature is 20°.
The coolest month in Illinois is January when the average maximum temperature is -0°, average temperature is -4° and average minimum temperature is -7°.
The longest days in Illinois are in June, with an average of 15.2 hours of daylight per day. December has the shortest days with an average of 9.2 hours of daylight per day.
The sunniest days in Illinois are in July which has the most hours of sunshine per day with an average of 11 hours of sunshine per day, making it a very sunny and pleasant month with long bright days. December has the least sunshine with an average of 3.6 hours of sunshine per day, making it not a particularly sunny month.
The ultraviolet index is the highest in June when it reaches 9.7 and lowest in December when it reaches 1.5.
An ultraviolet index reading of 8 to 10 indicates a very high risk of harm from unprotected sun exposure. Unprotected skin risks burning in less than 15 minutes. Take extra precautions because unprotected skin and eyes will be damaged and can burn quickly. Tanning will be safest before 10am and after 4pm but only with a good application of sun screen. For those with sensitive skin stay in the shade and wear protective clothing, a wide-brimmed hat, and UV-blocking sunglasses. Generously apply broad spectrum SPF 30+ sunscreen every 2 hours, even on cloudy days. Watch out for relections from water that may increase ultraviolet exposure.
The warmest sea water temperatures in Illinois are found in August when they peak at 28° and lowest in March when they dip to 20°.
The sea is best for swimming between June and December when the temperature is above 24° which is warm and pleasant for relaxing and swimming for long periods.
The wettest month in Illinois is August with 114.5cm of rain and June has the most days of rain with 13.8 days with some rain, a very wet time to visit the beach.
The driest month in Illinois is January with 38.4cm of rain and February has the fewest days of rain with 10.2 days with some rain, a slightly wet time to visit the beach.
The most humid month in Illinois is July with a dew point (an indicator of humidity) of 19° which is somewhat uncomfortable for most people in cities but fine on a beach.
The least humid month in Illinois is January with a dew point of -5° which is a bit dry for some.
The most windy month in Illinois is April when the average maximum windspeed is 33kmh and the average wind speed is 18kmh.
The least windy month in Illinois is September when the average maximum windspeed is 25kmh and the average wind speed is 13kmh.