Concord sits at the northern end of the Diablo Valley, a few miles south of Suisun Bay and the Carquinez Strait. That location makes it one of the Bay Area's hotter cities. July afternoons average around 90°F, and heat waves can push the temperature past 105°F. Concord is also close enough to the strait to catch a cooling breeze on most summer evenings. That breeze keeps it from baking the way towns deeper in the Central Valley do. Its weather is a mix of inland heat and late-day ocean air, with Mount Diablo rising to the southeast.
The Carquinez Corridor and Concord
The Carquinez Strait is a narrow channel between the hills that links San Pablo Bay to Suisun Bay and the Delta beyond. On summer afternoons, it acts as a doorway for ocean air. The thermal low over the hot Central Valley pulls cool air in through the Golden Gate, across the bay and east through the strait. Much of that flow becomes the Delta breeze, which cools Antioch, Fairfield and eventually Sacramento.
Concord sits just south of that stream of air. Some of the cool flow spills into the northern Diablo Valley in the late afternoon, giving the city welcome relief after the hottest part of the day. By the time the air arrives, though, it has crossed miles of warm water and land, so it is milder than the breeze along the coast. The result is a hot afternoon followed by a breezy, pleasant evening on most summer days.
Summer Temperatures and Heat Waves
July and August are Concord's hottest months, with average highs around 90°F. The swing between night and day is large. Summer mornings often start in the upper 50s, and the valley warms quickly once the sun is up. By early afternoon, a typical day is in the upper 80s or low 90s.
The afternoon sea breeze usually arrives from the north and west in the late afternoon. Once it does, the temperature can fall several degrees within an hour or two, and the evening turns comfortable for dinner outside.
Heat waves are a regular part of Concord summers. When a strong ridge of high pressure builds over the West, it weakens the flow of ocean air, and the breeze may not arrive at all. Temperatures can then reach 105°F or higher for several days in a row, and nights stay warm. Those stretches are dangerous for older adults, young children and anyone without air conditioning. Cooling centers open during the worst heat, and checking on neighbors matters.
Concord vs. Walnut Creek and Livermore
Concord, Pleasant Hill and Walnut Creek share the Diablo Valley, and on most summer days they run within a few degrees of each other. Concord, at the north end, tends to feel the late-day breeze from the strait a little sooner. Walnut Creek, farther south and closer to the hills, often stays warm a little later into the evening.
Livermore, about 25 miles to the south beyond Mount Diablo, has a similar summer climate. It gets its relief from a different route, though. Cool air reaches the Livermore Valley through gaps in the hills to its west. The Altamont Pass to its east then carries that air on toward the Central Valley. Average July highs in the two cities are close, and on any given day either one can be the hotter of the two.
During a strong heat wave, the differences mostly disappear. When the ocean air stops flowing, the whole inland East Bay heats up together, and towns from Concord to Livermore can all top 105°F. On ordinary summer days, the small differences come down to how soon each valley gets its evening breeze.
Spring in Concord
Spring is one of Concord's best seasons. From March through May, afternoons usually run in the upper 60s to upper 70s, and the hills around the valley turn bright green after the winter rains. Wildflowers cover the lower slopes of Mount Diablo in March and April. The trails in the state park and nearby open spaces are at their most pleasant then.
Spring is also the windiest time of year in much of the inland Bay Area. As the interior heats up and the ocean stays cold, the pull of ocean air grows stronger, and gusty afternoon winds blow through the valley. Late-season storms can still bring rain into April. By late May, the grass is turning gold, the first hot days arrive and the long dry season begins.
Fall and Winter
Fall brings relief from the heat. September can still be hot, but by October afternoons usually ease into the 70s and low 80s under clear skies. Many residents consider October the most pleasant month of the year, with warm days, cool nights and golden light on the slopes of Mount Diablo. Fall is also when dry offshore winds can blow, so fire danger in the surrounding hills stays high until the first good rain.
Winter is mild and fairly wet. Concord gets about 18 inches of rain in a typical year, less than San Francisco's roughly 23 inches. Nearly all of it falls from November through April. Winter afternoons are usually in the upper 50s, and clear nights can bring frost to lawns and car windows.
On calm winter mornings, tule fog sometimes drifts in from the Delta or forms right over the valley floor. It can cut visibility on Highway 4 and Interstate 680 and linger until late morning before the sun burns it off. That mix of hot summers, foggy winter mornings and frosty nights gives Concord a more inland character than most Bay Area cities.
