Historical weather data, all-time temperature records, and monthly climate averages for Altadena, CA. Explore typical weather conditions by week for trip planning, and see how today compares to the historical record.
April 5th in Altadena typically feels like a mild spring day, with average highs of 73° and lows near 49°. But history shows the range can be wild — this date has swung from a frigid 33° in 1921 all the way to a scorching 101° in 1989. There's a 23% chance of rain today, so a jacket isn't the worst idea.
Altadena plays in extremes. The mercury has climbed as high as 115° — reached during the brutal September 2020 heat wave — and plunged to 21° back in January 1913. A single storm dropped 7.7 inches of rain on March 2, 1938, and yes, it has snowed here: 3 inches fell on January 11, 1949.
Altadena is warm and sunny almost year-round, with average highs never dipping below 66° even in the coldest first week of January. Peak heat arrives late July through early August, when highs average 90°. If you're trying to dodge rain, avoid late February — it's the wettest stretch of the year, averaging over an inch of precipitation in a single week.