Historical weather data, all-time temperature records, and monthly climate averages for Rialto, CA. Explore typical weather conditions by week for trip planning, and see how today compares to the historical record.
April 5 in Rialto lands in that sweet spot of spring, with average highs of 74° and lows of 46° — warm afternoons, crisp nights. There's a 17% chance of rain, which is modest but not impossible; on the extreme end, this date has seen highs hit 92° and lows dip to a surprising 33°.
Rialto is a place of genuine extremes, sitting in the shadow of the San Bernardino Mountains where heat and cold both arrive with force. The thermometer has swung from a brutal 113° in September 1955 all the way down to 20° in January 1949 — and that same January week dropped 6.5 inches of snow, a figure that feels almost surreal for inland Southern California.
Summer dominates Rialto's calendar hard — highs average 95° through July and August, making it one of the hotter corners of the LA basin. If you're heat-averse, aim for January through March, when highs settle in the low-to-mid 60s. Rain is scarce year-round but concentrates in late January, the wettest stretch averaging just under an inch for the week.