Study Shows Northern California’s Summers Are Lasting Longer Than Ever

Summers in Northern California aren’t just getting hotter, they’re getting longer. A new Washington Post analysis shows that the hottest 90 days of the year now arrive earlier and linger later, stretching summer well into what used to be spring and fall.

In Sacramento, the season of triple-digit highs has expanded by more than a month compared to the mid-20th century, keeping residents sweltering deep into September. Redding, already known for blistering summers, now sees its hottest stretch extend by several weeks, putting extra strain on air conditioning systems and wildfire crews.

Even coastal communities, once shielded by marine fog, are feeling the shift. San Francisco has added over 40 days of “summer heat” since 1970, and nearby Santa Rosa is recording longer, hotter shoulder seasons.

This shift is fueled by a warming planet. With oceans absorbing and releasing more heat, and local fog cover diminishing, the cooling relief Northern Californians once relied on is fading. The result: longer wildfire seasons, heightened health risks during extended heat waves, and more pressure on water resources already stretched thin.

These changes are reshaping outdoor life. From Lake Tahoe to Mount Shasta, recreation calendars are shifting as extreme heat encroaches on prime hiking and camping months. Communities must adapt with better cooling strategies, greener urban planning, and wildfire preparedness. Because Northern California’s “new normal” summer is sticking around for the long haul.