California heat wave arrives — but the Bay Area stays in its own climate bubble
That contrast stems from two competing players in the atmosphere. On one side: a classic summertime ridge of high pressure building out of the interior West, delivering dangerous heat to the Southwest, the Inland Empire and Southern California. That's competing against an unusually cool ocean, chilled by weeks of persistent northwest winds and vigorous upwelling, all powered by the position of the North Pacific High.
It's noticeably chilly thx to ongoing cooler than normal east Pac sea surface temp, sea breezes. June-July avg temps so far along coast cooler than 1991-2020 normals. San Francisco June-July to date avg temp 57.6F tied 17th coolest on record, coolest since same period 1999. #CAwx pic.twitter.com/V1P6GdltMG
— NWS Bay Area 🌉 (@NWSBayArea) July 5, 2025
Starting Wednesday, those two competing features will begin to clash. It's not a dramatic battle, but a quieter atmospheric tug-of-war, with warm, sinking air from aloft trying to flood the state, held in check by the cool, stubborn marine layer.
Through Friday and into the weekend, high pressure will build across Southern California and the Southwest, generating widespread temperatures in the 100 to 115 degree range inland, and temperatures in the 90s in the interior valleys close to Los Angeles and San Diego.
But that ridge won't be able to spread too far northward. A second high, parked off the Pacific Northwest, will block its path, forcing the southern ridge of high pressure to stretch sideways from the Channel Islands to Arizona.
This setup reinforces a daily strong onshore flow along the California coast, with persistent westerly winds pushing the marine layer inland each day. It's a familiar battle for July, but this time, the marine layer is getting a boost in part by colder than normal ocean temperatures.
That cool, dense air spills through the Golden Gate and other coastal gaps, spreading across San Francisco and up against the East Bay Hills and the Santa Cruz Mountains.
The result? A dramatic thermal contrast at the surface with temperatures in the 60s and 70s near the coast, rising to 80s and 90s inland and triple digits across the Central Valley.
Wednesday breakdown
San Francisco: Another morning with extensive cloud cover across the city with some patchy pockets of drizzle, giving way to mostly sunny skies by the afternoon. Temperatures will be a tad bit warmer, with highs in the low 60s along the water and the upper 60s downtown. Clouds return to the west side of the city overnight with low temperatures in the mid-50s.
North Bay: Clouds will extend back through Napa and Vallejo on Wednesday morning before sunshine develops in the afternoon, except at the immediate coast. Temperatures will be trending warmer with highs in the 80s in Novato, Santa Rosa and Napa. Mild with mostly clear skies overnight and lows in the 50s.
East Bay: Clouds will be thick west of the Berkeley hills in the morning, with sunshine developing across the entire East Bay by the afternoon. Highs will be in the low to mid-70s in Richmond, Oakland and Hayward and highs will be in the low 80s in the Tri-Valley. Mostly clear overnight with lows in the 50s.
Pacific Coast and Peninsula: The immediate coast in places like Pacifica and Half Moon Bay will hang onto some cloud cover for the duration on Wednesday, with temperatures in the low 60s. Sunshine will break out across the rest of the Peninsula for a pretty nice day with highs in the upper 60s in South San Francisco to the upper 70s in Redwood City. Cloudy along the coast with partly clear skies elsewhere overnight and lows in the 50s.
South Bay and Santa Cruz: It's a cloudy start to Wednesday in the South Bay and in Santa Cruz, but sunshine will be widespread by the late morning. Highs will be in the upper 70s to low 80s in Sunnyvale, San Jose and Campbell, with highs in the upper 70s in Santa Cruz. Mostly clear overnight with lows in the 50s.
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Three dead as South Korean region hit by most rain in 120 years
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San Francisco Chronicle
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This is what is keeping California cool while the rest of the U.S. sizzles
While much of the country has endured a barrage of historic floods and punishing heat and humidity this month, California's summer has been surprisingly tame. The Bay Area is already on track for one of its coolest starts to summer in decades, and forecast data suggest that trend isn't going anywhere. The Climate Prediction Center calls for continued below average temperatures across the state, essentially through the end of the month. The lingering cool trend is a result of a broader atmospheric setup that's been locked in for weeks. East of the Rocky Mountains, a sprawling and stubborn Bermuda high pressure system is pumping in heat, humidity and bouts of heavy rain. But over California, the jet stream has flattened into a fast-moving west-to-east flow of winds, interrupted only occasionally by subtle dips in the upper atmosphere. UCLA climate scientist Daniel Swain described this pattern as a ' sticky weak disturbance,' and the setup has been on repeat since early June. The airflow around a stronger than normal North Pacific High continues to stir up cooler water along the West Coast, while driving a surge of warm water across the central Pacific. This sets up a positive feedback loop; cooler coastal waters sharpen the daily temperature and pressure gradients from the ocean to the Central Valley, which enhance onshore winds and reinforce the cloud deck. The result is more marine layer influence, lower high temperatures, especially near the coast. It's not just the coast that's feeling the cooler temperatures. Inland areas that typically bake this time of year like the Central Valley, interior Bay Area and the high deserts, have struggled to mount any multiday heat waves. The kind of prolonged, widespread heat events California saw in July 2024 require a robust high pressure ridge centered closer to California, something that just hasn't materialized so far this summer. The extended 8- to 14-day temperature outlook shows a similar pattern, with continued cool conditions across California. Still, the state won't avoid the heat altogether. Brief surges into the triple digits remain likely in places like Redding, Fresno and Palm Springs. But those hot spells will be short-lived and the marine influence will remain strong along the coast. The cooler temperatures, both daytime and overnight, help tamp down fire weather risks. But as we push deeper into summer and fuels continue to dry, fire activity is still expected to increase. Wednesday's weather in the Bay Area will be a continuation of the pattern, with daytime highs running about 10 degrees below normal and marking the coolest day of the week. Wednesday outlook San Francisco: A thick marine layer will generate patches of drizzle in the early morning. And from there, the clouds will be slower to retreat to the coast than yesterday. But retreat they will, leaving a mostly sunny Wednesday afternoon and evening. Temperatures will top out in the low 60s west of the Twin Peaks and in the mid-60s downtown and in the Mission. Winds from the southwest pick up during the afternoon and clouds will return after dark, with lows in the mid-50s. North Bay: Pockets of drizzle will develop in Santa Rosa and along the Marin coast in the morning. Cloud cover from the marine layer will extend all the way back to Fairfield, but they will quickly break up by the early afternoon. Despite the sunshine, it's another cool day, with temperatures in the low to mid-70s. More clouds and drizzle overnight with lows in the 50s. East Bay: A thick cloud deck will extend all the way to I-680 in the morning. Things will clear up rather quickly across the interior and south of Oakland, with clouds hanging on a bit longer in Berkeley and Richmond. Temperatures will range from the upper 60s to low 70s in the I-580/I-80 stretch, with highs in the mid-70s to around 80 degrees in Hayward, Concord and Livermore. Mostly cloudy again overnight with lows in the mid- to upper 50s. Pacific Coast and Peninsula: Does the Pacific Coast see the sun this day? It's a tossup. Some sunshine may break through the clouds in the afternoon from Half Moon Bay up to Pacifica with temperatures in the low 60s. The rest of the Peninsula east of Skyline Boulevard will clear up earlier, with temperatures ranging from the upper 60s in South San Francisco, the low 70s in San Mateo and the mid-70s in Redwood City. The clouds return overnight with pockets of drizzle along the coast and lows in the 50s. South Bay and Santa Cruz: A predominantly southwesterly wind will keep the clouds locked and temperatures muted for a good part of the day in Santa Cruz, where it will be a struggle to hit 70 degrees. The South Bay will once again be the warm spot in the region, with temperature in the low 80s. Mostly cloudy again overnight with lows in the mid-50s.
San Francisco Chronicle
09-07-2025
- San Francisco Chronicle
California heat wave arrives — but the Bay Area stays in its own climate bubble
A clash of summer forces is unfolding across California this week, and the Bay Area is caught right in the middle of it. Starting Wednesday, a moderately strong heat wave will take shape inland, but its reach will be uneven and the coast may barely feel it at all. That contrast stems from two competing players in the atmosphere. On one side: a classic summertime ridge of high pressure building out of the interior West, delivering dangerous heat to the Southwest, the Inland Empire and Southern California. That's competing against an unusually cool ocean, chilled by weeks of persistent northwest winds and vigorous upwelling, all powered by the position of the North Pacific High. It's noticeably chilly thx to ongoing cooler than normal east Pac sea surface temp, sea breezes. June-July avg temps so far along coast cooler than 1991-2020 normals. San Francisco June-July to date avg temp 57.6F tied 17th coolest on record, coolest since same period 1999. #CAwx — NWS Bay Area 🌉 (@NWSBayArea) July 5, 2025 Starting Wednesday, those two competing features will begin to clash. It's not a dramatic battle, but a quieter atmospheric tug-of-war, with warm, sinking air from aloft trying to flood the state, held in check by the cool, stubborn marine layer. Through Friday and into the weekend, high pressure will build across Southern California and the Southwest, generating widespread temperatures in the 100 to 115 degree range inland, and temperatures in the 90s in the interior valleys close to Los Angeles and San Diego. But that ridge won't be able to spread too far northward. A second high, parked off the Pacific Northwest, will block its path, forcing the southern ridge of high pressure to stretch sideways from the Channel Islands to Arizona. This setup reinforces a daily strong onshore flow along the California coast, with persistent westerly winds pushing the marine layer inland each day. It's a familiar battle for July, but this time, the marine layer is getting a boost in part by colder than normal ocean temperatures. That cool, dense air spills through the Golden Gate and other coastal gaps, spreading across San Francisco and up against the East Bay Hills and the Santa Cruz Mountains. The result? A dramatic thermal contrast at the surface with temperatures in the 60s and 70s near the coast, rising to 80s and 90s inland and triple digits across the Central Valley. Wednesday breakdown San Francisco: Another morning with extensive cloud cover across the city with some patchy pockets of drizzle, giving way to mostly sunny skies by the afternoon. Temperatures will be a tad bit warmer, with highs in the low 60s along the water and the upper 60s downtown. Clouds return to the west side of the city overnight with low temperatures in the mid-50s. North Bay: Clouds will extend back through Napa and Vallejo on Wednesday morning before sunshine develops in the afternoon, except at the immediate coast. Temperatures will be trending warmer with highs in the 80s in Novato, Santa Rosa and Napa. Mild with mostly clear skies overnight and lows in the 50s. East Bay: Clouds will be thick west of the Berkeley hills in the morning, with sunshine developing across the entire East Bay by the afternoon. Highs will be in the low to mid-70s in Richmond, Oakland and Hayward and highs will be in the low 80s in the Tri-Valley. Mostly clear overnight with lows in the 50s. Pacific Coast and Peninsula: The immediate coast in places like Pacifica and Half Moon Bay will hang onto some cloud cover for the duration on Wednesday, with temperatures in the low 60s. Sunshine will break out across the rest of the Peninsula for a pretty nice day with highs in the upper 60s in South San Francisco to the upper 70s in Redwood City. Cloudy along the coast with partly clear skies elsewhere overnight and lows in the 50s. South Bay and Santa Cruz: It's a cloudy start to Wednesday in the South Bay and in Santa Cruz, but sunshine will be widespread by the late morning. Highs will be in the upper 70s to low 80s in Sunnyvale, San Jose and Campbell, with highs in the upper 70s in Santa Cruz. Mostly clear overnight with lows in the 50s.
