Historical weather data, all-time temperature records, and monthly climate averages for Oswego, IL. Explore typical weather conditions by week for trip planning, and see how today compares to the historical record.
April 4th in Oswego sits squarely in the awkward stretch of spring — expect a high near 55° and a low that can still bite at 33°. The date's 130-year range tells the whole story: it's hit 81° (1929) and plunged to 14° (1975), so anything goes. There's a 38% chance of rain, but snow is mostly off the table at just 4%.
Oswego's weather history is not for the faint of heart — the thermometer has swung from a brutal -26° in January 1985 all the way to a scorching 111° in July 1936, a range of 137 degrees. The wettest single day on record dumped a staggering 16.91 inches of rain on July 18, 1996, and a February 2011 snowstorm buried the town under 17 inches in one shot.
Summer is the clear sweet spot, with late July averaging a high of 86° and June bringing the most rainfall at just over an inch per week — great growing weather, less ideal for outdoor events. Winter is genuinely cold: early January averages a high of only 31°, so plan accordingly. Spring and fall offer a wide temperature spread, with April highs averaging 60° and October a pleasant 64°.