Historical weather data, all-time temperature records, and monthly climate averages for Round Lake, IL. Explore typical weather conditions by week for trip planning, and see how today compares to the historical record.
April 5th in Round Lake sits squarely in that unpredictable shoulder season — the average high is only 51° with a low dipping to 32°, so frost is still on the table. The date's history backs that up: temperatures have swung from a bitter 14° in 1995 to a shirt-sleeve 75° in 2021, a 61-degree spread across 47 years of records.
Round Lake doesn't mess around at the extremes — this is a place that has cooked at 101° and frozen at -32°, a swing of 133 degrees between its all-time records. The coldest day on record came as recently as January 31, 2019, a reminder that brutal polar outbreaks are very much a modern reality here.
Summer is the clear sweet spot, with average highs peaking around 83-84° in mid-July and the wettest stretch of the year arriving right alongside it in late June. If you're avoiding the cold, steer clear of mid-January when highs average just 26°. Spring and fall are transition seasons in the truest sense — April highs average 58° but the thermometer is still capable of anything.