2 days ago
- Climate
- San Francisco Chronicle
Here's why forecasters see California turning red on this map
California's first real taste of summer arrived recently, with temperatures pushing triple-digit highs from Redding to Palm Springs, heat more typical of July than spring. Yet during last week's heat wave, due to fog pooled beneath the Golden Gate Bridge that spilled over western San Francisco, afternoon highs only hit the low 60s in San Francisco. Meanwhile, just 30 miles inland, Concord baked at 100 degrees.
These sharp temperature contrasts mark a California summer rite of passage, but forecasts suggest a less pronounced divide for future heatwaves this year. That's because coastal areas may have to rely on a thinner marine layer, which means less of the cooling ocean air that typically allows places like S.F. to stay comfortable.
According to the seasonal outlook from NOAA's Climate Prediction Center, most inland areas in California have a 60% to 70% chance of experiencing one of the warmest summers since 1991. This forecast extends a clear warming trend. California's average summer temperature has come in above the 1991–2020 climatological normal every year since 2012. The run peaked in 2024, the hottest summer for California in over 100 years, when Sacramento, Stockton, Redding and San Jose all shattered their all-time seasonal heat records. This summer, even traditionally mild coastal cities face a coin‑flip level chance for above normal warmth, hinting that the marine layer may not offer its usual insulation.
Rain won't offer relief either this summer and that's no surprise. California summers are historically dry and the Climate Prediction Center's 'equal chances' designation simply means the long range forecast models see no clear signal to tip the odds toward wetter or drier conditions. In practical terms, the state can expect its familiar pattern of scant summer rainfall even as the temperature outlook climbs.
'There really isn't much push from El Niño, La Niña, or other classic climate drivers,' said Johnna Infanti, a forecaster with the Climate Prediction Center. 'Yet every major model we run is pointing toward heat from June through August.'
Why are the forecast models so sure of the heat? UCLA Climate scientist Daniel Swain sees two forces at work.
First, he says, is the rising baseline: 'Climate change means most recent summers already start warmer than the 30- to 40-year average.' Second is an ocean pattern forecast models clearly detect even if meteorologists are not exactly sure what it is. As Swain puts it: 'There is something in the initial state of the Earth system — mostly the sea-surface-temperature pattern beyond ENSO, that is forcing this persistent very hot signal. We know it isn't El Niño, so it has to be something else, and we may not even have a clear name for it yet.'
California's trend of increasingly severe heat waves illustrates these warnings. Cities statewide have witnessed a notable uptick in extremely hot days. Last summer shattered heat records across several locations, including Sacramento, Fresno, Bakersfield and Redding, each experiencing significantly more triple-digit days than their historical averages.
Even more concerning are increasingly warm summer nights, disrupting the critical overnight cooling that communities depend on for recovery from daytime heat. The Climate Prediction Center's latest outlook suggests 2025 will once again deliver an above‑average run of 100‑degree afternoons and unusually warm overnight lows across much of the state.
The hotter, drier backdrop will impact the fire season as well. Cal Fire and the National Interagency Fire Center reported that a lush grass crop is drying weeks ahead of schedule in Southern California. Sparse winter rains in that region left soils thirsty and vegetation quick to brown. The summer outlook shows July with above normal large fire potential over nearly all of Northern California and much of the Sierra and Coast Ranges. That risk expands to nearly the entire state by August, as persistent heat and drought-stressed fuels could push fire activity above normal this summer.
The Southwest monsoon activity signals are mixed this year. Sea surface temperatures in the Gulf of California are running above normal, a warm bath that can fuel northbound moisture pulses. The Madden‑Julian Oscillation, a slow‑moving pulse of tropical thunderstorms that circles the globe every 30 to 60 days, is forecast to stay active into late June. And if that pulse coincides with a strengthening of the ridge of high pressure, it could help pull more monsoon moisture north in July. Meanwhile, NOAA calls for a subdued eastern Pacific hurricane season, a key late summer moisture source. Taken together, forecasts show no strong tilt toward a wetter or drier monsoon.
As July and August approach, prolonged heat waves, particularly inland, seem increasingly likely.
'The models were really, really, really insistent on above‑normal temperatures across the entire U.S., not just over the West,' Infanti noted.
California should brace for another exceptionally hot and largely dry summer, with inland valleys racking up many more 100‑degree days than usual and nights that stay uncomfortably warm.
