Historical weather data, all-time temperature records, and monthly climate averages for Grayslake, IL. Explore typical weather conditions by week for trip planning, and see how today compares to the historical record.
April 5 in Grayslake runs cool, with an average high of just 51° and a low that can still dip to freezing. The date has swung wildly over 47 years of records — from a 75° stunner in 2021 to a brutal 14° in 1995. There's a 1-in-3 chance of rain today, though snow is unlikely at just 5%.
Grayslake earns its Midwest stripes with a staggering 133-degree spread between its all-time extremes — 101° in July 1995 and -32° on the last day of January 2019. A single July day in 1985 dropped 4.77 inches of rain, and a February 2011 snowstorm buried the area under 17.3 inches in one shot.
Summer is the clear sweet spot, with highs peaking around 83-84° in mid-July and the warmest stretch running July 16–22. Winters are genuinely harsh — mid-January averages just 26° for a high, and January and February rarely crack freezing. Plan for the wettest conditions in late June through early July, when a typical week brings over an inch of rain.