Winters in St. Charles are cold and variable, with temperatures often dropping below freezing for extended periods, but occasional warmer days can bring temperatures into the mid-teens. As spring approaches, temperatures gradually warm up, with March marking a significant shift towards milder conditions, while April and May bring further increases in temperature. Summers are warm to hot, with July and August being the warmest months, although diurnal temperature ranges remain relatively modest. Autumn is characterized by a return to cooler temperatures, with September often feeling quite pleasant before November's chill sets in. During winter months, frosts and freezes are common, but December's mild days can be a welcome respite from the cold.