Historical weather data, all-time temperature records, and monthly climate averages for Alton, IL. Explore typical weather conditions by week for trip planning, and see how today compares to the historical record.
April 5th in Alton typically feels like a coin-flip kind of spring day — average highs around 60° with lows in the low 40s. The date's range tells the real story though: it's reached 89° (back in 1946) and bottomed out at 23° (1987), so the calendar says spring but the weather isn't always listening. Rain is a modest 31% chance, and snow is essentially off the table.
Alton's weather history doesn't mess around — the city holds one of the most extreme temperature swings in the Midwest, from a scorching 116° on July 10, 1946 to a brutal -16° on January 10, 1982, a range of 132 degrees. April is when the region gets its biggest soakings, as evidenced by the all-time wettest day of 7.7 inches falling on April 23, 1996.
Alton peaks in mid-July with average highs of 88–89° and bottoms out in mid-January around 37°. If rain is your concern, avoid late April — the week of April 23rd averages over an inch of precipitation and produced the city's all-time rainfall record. Spring and fall offer the most comfortable travel windows, with highs in the 60s and 70s through April–May and again in September–October.