Historical weather data, all-time temperature records, and monthly climate averages for Hercules, CA. Explore typical weather conditions by week for trip planning, and see how today compares to the historical record.
April 4th in Hercules typically brings mild spring conditions with an average high of 67° and just a 19% chance of rain. But the date has seen some wild swings — temperatures have ranged from a chilly 39° low back in 1963 all the way up to a scorching 89° high in 2011.
Hercules sits in the San Francisco Bay's moderating influence, but the extremes still impress — the thermometer once hit 107° on September 14, 1971, and plunged to 24° on December 9, 1972. A single January day in 1982 dumped 6.83 inches of rain, and yes, it has technically snowed here, though just barely: 0.1 inches in April 1999.
Hercules runs cool and mild year-round, with highs barely budging between 56° in early January and a peak of 75° in late September. Summer is pleasant rather than hot, and the rainy season is squarely in winter — mid-February is statistically the wettest stretch of the year. If you're chasing warmth, late September is your best bet; if you're avoiding rain, May through October is reliably dry.