Brentwood Weather

March through May are unbeatable for Brentwood. March scored a 94 comfort rating with highs around 72F and 11 hours of daily sunshine. April climbed to 91 with 82F highs, and May delivered 92 with nearly 14 hours of sun per day. These spring months are warm enough for short sleeves but never oppressive, and the agricultural landscape is at its most vibrant. If spring doesn't work, September is an excellent alternative with a 91 comfort score, highs near 74F, and the worst of summer heat broken. The months to avoid are November and December, when comfort scores plummet to 64-71, fog increases to 3-4.5 hours per morning, and rain becomes frequent. Understanding the Bay Area's four seasons helps explain why spring is so perfect here: the region shifts from cool winters to warm, stable weather without marine layer interference.

Dramatically hotter. While San Francisco rarely exceeds 75F in summer due to marine fog, Brentwood's June average sits at 98.5F, July at 94F, and August at 91F. This 20-25F difference reflects Brentwood's inland position, far from the cooling Pacific influence. Heat events above 100F are not uncommon from late June through July. The Bay Area's microclimate system creates these dramatic differences: the marine layer cools the coast while the inland valley amplifies solar heating. Morning lows in the 60s do provide some relief, making early mornings and evenings the best times for outdoor activities during summer. If you visit mid-June through August, plan activities before 10am or after 6pm to avoid peak heat.

Clothing needs shift dramatically by season. Summer requires aggressive sun protection: high-SPF sunscreen, wide-brimmed hat, lightweight and breathable fabrics. With 12-13 hours of daily sunshine, the sun here is relentless. Bring a light jacket for evenings when temperatures drop 30-35 degrees from afternoon highs. Spring and fall packing is easier: t-shirts and shorts for afternoons, a light jacket for mornings and evenings. Winter demands rain gear for the concentrated wet season (October-January) and a real jacket for evenings when lows drop into the 40s. Unlike coastal Bay Area towns where fog demands constant layering, Brentwood's swings are primarily temperature-driven. Dressing in layers for Bay Area weather applies here, though the dynamic is different from foggy coastal neighborhoods.

Approximately 57 rainy days per year, making Brentwood one of the drier Bay Area destinations. Rainfall is heavily concentrated in October through January, when the region receives 3-5 inches monthly. January 2025 was the wettest month at 4.86 inches, while May and June recorded essentially zero rainfall. This Mediterranean pattern means five months of near-total dryness from May through September. About 260 days per year qualify as perfect weather days, giving Brentwood over 70% favorable conditions annually. The Bay Area's rainiest month patterns show how regional weather varies, and Brentwood's eastern location puts it on the drier end of the spectrum.

Yes, for most of the year. April and May are ideal: highs in the low 80s, near-zero fog, and comfortable evening temperatures make dining outside genuinely pleasant. Spring also delivers the highest comfort scores (91-94), so ambient conditions are at their best. Summer (June-August) is hot but works in early mornings or after 6pm when temperatures moderate. September-October offer a second window with comfort scores in the high 80s. November and December are the real challenge, with comfort scores dropping to 64-71, temperatures in the 50s, and fog or overcast skies becoming common. Winter outdoor dining requires supplemental heat and rain planning. For the most reliable outdoor dining experience, target April-May when Brentwood's weather is at its absolute best.

Barely by Bay Area standards. Across the 18-month observation period, Brentwood averaged just 1 hour of morning fog daily. Summer months are virtually fog-free: June and May recorded essentially zero fog. Even when fog does appear, it's typically valley radiation fog that burns off by late morning, not the stubborn marine layer that blankets coastal towns. Late fall sees a temporary increase, with November averaging 4.5 fog hours and October 2.8 hours, but this is still minimal compared to foggy neighborhoods 30 miles away. Understanding how fog forms along the Northern California coast reveals why inland Brentwood stays so clear: the marine layer forms over ocean and coastal hills, then either gets trapped by coastal ranges or burns off before reaching the inland valley. Brentwood's position means sunshine, not fog, dominates the landscape.

Antioch sits just a few miles northwest and shares Brentwood's hot, dry inland character. Both towns are largely fog-free and receive most of their rain in winter. The subtle difference is Antioch's proximity to the San Joaquin Delta gives it more exposure to delta breezes, potentially providing afternoon wind relief during peak heat. Brentwood, sitting slightly further east and more sheltered, can run a few degrees hotter on the most intense summer days. Both towns contrast sharply with coastal Bay Area destinations 50 miles away. For hiking Black Diamond Mines Regional Preserve that sits between them, morning visits in summer are essential before afternoon heat peaks.

November and December are significantly less pleasant than the rest of the year. Comfort scores drop to 64-71, the lowest of any months. November averages 4.5 hours of morning fog and 4.23 inches of rain, December brings 2.58 inches of rain and occasional fog at 0.6 hours per morning. Temperatures are cool, typically 54-58F highs with lows in the low 40s. The abundance of rain and fog, combined with reduced sunshine (4.8-6.5 hours daily), makes outdoor activities less appealing. January is slightly better as winter settles in. February begins the recovery toward spring. If you have flexibility, avoid November-December and visit during spring (91-94 comfort) or September (91 comfort) instead.

An outstanding 9.7 hours per day on average, nearly double some foggy Bay Area locations. Summer months deliver 11-13.7 hours of daily sunshine. June sees 13.3 hours, July 12.4 hours, and May a remarkable 13.7 hours. Even winter months average 5-8 hours of daily sun. This sunshine abundance explains why Brentwood's average comfort score of 83/100 remains high despite summer heat: sunshine is weighted heavily in comfort calculations. By comparison, foggy San Francisco sees perhaps 5-6 hours of summer sun while Brentwood enjoys more than double that. The high sunshine hours make spring and early fall ideal for activities that require good daylight conditions.

Brentwood experiences dramatic 25-35 degree swings between morning and afternoon throughout the year. A typical spring day might dawn at 48F and climb to 72F by late afternoon. Summer swings are even more pronounced: mornings in the 60s rapidly climbing to 95F+ afternoons. This wide range is characteristic of inland valleys without marine moderation. The consistency of this pattern makes Brentwood easier to plan for than foggy coastal towns where temperatures remain cool and unpredictable all day. Bring layers you can peel off as the day warms. Outdoor activities are best during late morning through early evening when temperatures are moderate. Winter swings are narrower but still substantial, perhaps 40F mornings reaching 58F afternoons, requiring morning and evening jackets.