Walnut Creek Weather

April is the sweet spot. In April 2025, Walnut Creek averaged highs of 78°F, logged 12.8 hours of sunshine per day, and saw almost no rain (just 0.16 inches for the entire month) with a comfort score of 90 out of 100. That combination of warmth, long days, and minimal fog is hard to beat anywhere in the Bay Area. May runs a close second, also posting a comfort score of 89 with highs near 79°F and zero precipitation. March is worth mentioning too: highs around 71°F, nearly 11 hours of sun, and a comfort score of 89. Spring in Walnut Creek hits differently than spring on the coast. The hills are green, temperatures are warm without being oppressive, and the outdoor dining on Locust Street is genuinely pleasant rather than aspirational. If you can only pick one window, aim for the last two weeks of April into early May. You get summer-quality sunshine without summer heat, and the Diablo foothills backdrop is at its most photogenic.

Hot, and that is not a bad thing for everyone. July and August both average highs in the mid-to-upper 80s, with July 2024 reaching 86°F and July 2025 hitting 85.6°F. Heat spikes do occur, especially in late July and August when inland valleys can push into the mid-90s or higher during extended heat events. What the averages do not capture is how quickly the evenings cool down. Walnut Creek sits in the Contra Costa hills where overnight lows stay in the upper 50s even in peak summer, so sleeping conditions are comfortable even when afternoons get intense. The diurnal swing of 25 to 30 degrees is the real story. Afternoons can feel relentless, but by 7 p.m. a Delta breeze typically rolls in and knocks temperatures back. This is a big part of why the Bay Area has so many microclimates: just 20 miles west in Oakland, those same July afternoons average closer to 70°F. Walnut Creek is firmly in the warm-interior camp.

On a typical summer day, Walnut Creek runs 15 to 20 degrees warmer than San Francisco. When the city is sitting at 62°F under fog, Walnut Creek is often at 82°F under clear sky. The gap narrows in winter: both cities see highs in the upper 50s to low 60s, though Walnut Creek tends to get slightly colder overnight lows because it lacks the ocean's thermal moderation. The reason for the summer disparity is straightforward. San Francisco sits at the mouth of the Bay where cool marine air pours through the Golden Gate all summer long. Walnut Creek is sheltered behind the Berkeley Hills and Mount Diablo, so that marine air arrives weakened and sometimes not at all. On fog-heavy days in the city, the hills act as a literal barrier and Walnut Creek bakes in sunshine. This dynamic makes it one of the most reliably warm destinations in the region for anyone who finds San Francisco summers disappointing. If you want to understand the mechanics behind this pattern, why the Bay Area has so much wind explains the pressure gradients that drive cool air toward the coast and leave interior valleys warm.

Less than much of the Bay Area, but it is not completely fog-free. The 18-month data shows an average of 1.7 hours of morning fog per day across all seasons. That number climbs noticeably in fall: October and November 2025 each recorded over 3 hours of morning fog per day, with November hitting 4.3 hours. This is the classic tule fog pattern, where calm, cool autumn nights allow radiation fog to settle into the inland valleys. It is a different animal from the marine fog that blankets San Francisco and the coast. Tule fog typically forms after midnight and burns off by mid-morning, leaving a perfectly clear afternoon. Summer fog is minimal. June through September averages well under 2 hours per day, with September 2024 dropping to just 0.6 hours. Spring is the clearest stretch overall: April 2025 logged only 0.5 hours of morning fog per day. The short answer is that morning fog in Walnut Creek is a brief inconvenience rather than an all-day weather story. For more on how and why Bay Area fog forms, this piece on morning fog walks through the mechanics.

Rain is concentrated almost entirely in November through March, following the Bay Area's Mediterranean climate pattern. January is typically the wettest month, and January 2025 confirmed that with 5.08 inches for the month. November and October are also consistently wet: November 2025 brought 4.79 inches, and October 2024 delivered 4.68 inches. Summer is essentially dry. June, July, and August all registered zero or near-zero precipitation in both 2024 and 2025. May and September also tend to stay dry, making the warm-season window about five months of reliable sunshine. Across a full year, Walnut Creek sees roughly 61 rainy days. That leaves about 267 days the data classifies as perfect, which aligns with what you would expect from a town that markets itself as a sunny inland destination. December can be deceiving: the 2024 and 2025 December numbers were relatively mild (0.71 and 2.57 inches respectively), but atmospheric river events can dump several inches in a single storm. For more on the wettest periods region-wide, Bay Area rainy season patterns has the full picture.

For most of the year, yes, and this is one of Walnut Creek's genuine strengths as a dining destination. The downtown Locust Street corridor has outdoor seating that gets real use from March through November. April through October is the prime window: averages stay in the 60s through 80s during the day, evenings cool but rarely drop below 50°F until November. Summer afternoons can push into the mid-to-upper 80s, which makes shaded patio seating more comfortable than full-sun spots. The Delta breeze usually arrives by early evening and takes the edge off. Winter outdoor dining is possible but requires some tolerance for cool evenings. December and January see overnight lows dropping into the low 40s, so a heavier layer and a heat lamp setup help. November is the month where outdoor dining starts to feel like a commitment rather than a pleasure: fog is more frequent, temperatures are lower, and the November 2025 comfort score dropped to 64, the lowest of the 18-month period. If you are planning a dinner reservation with a patio in mind, aim for May through September for the most consistently comfortable experience.

The packing list depends heavily on which season you visit, and that variability is the one thing to plan around. In summer, lightweight clothing handles the warm afternoons, but always bring a layer for evenings. The Delta breeze can drop temperatures 15 to 20 degrees between 3 p.m. and 8 p.m., and a linen shirt that felt perfect at lunch feels inadequate by dinner. Sunscreen is non-negotiable from April through October: Walnut Creek logs 10 to 13 hours of sunshine per day in those months, more than almost anywhere else in the Bay Area. In spring and fall, the classic Bay Area layering approach applies: start with a base layer, add a light jacket in the morning, and peel it off by noon. Winter visits call for a proper mid-weight jacket and an umbrella or packable rain shell. The rain is infrequent by Pacific Northwest standards but arrives fast when it does, and the walk from a parking garage to a restaurant can get very wet very quickly. Comfortable walking shoes are worth prioritizing year-round given the amount of ground most people cover in the downtown area.

This is a genuine weather pattern and not just a perception. The data bears it out: September 2024 averaged a high of 82.5°F while July 2024 came in at 86°F, but the character of the heat is different. Late summer and early fall often produce what locals call the second summer or heat season, when the marine layer weakens and offshore flow allows hot, dry air from the interior to push back toward the Bay. September 2025 averaged highs of 72.9°F but those averages include cooler cloudy days and hide the heat spike potential in late September and early October. The why September is hotter than July in the Bay Area article covers this in detail, but the short version is that the marine layer is at its weakest in September and offshore events can produce triple-digit temperatures in the East Bay valleys. Walnut Creek is particularly exposed to this dynamic given its inland position. If you dislike heat, this is the one seasonal quirk worth tracking before a fall visit.

All three towns share a similar inland microclimate, but with subtle differences worth knowing. Concord sits a few miles further inland and north of Walnut Creek, which tends to make it slightly hotter in summer and more prone to tule fog in fall and winter. The effect is modest but real. Lafayette is positioned a bit closer to the Berkeley Hills and the Caldecott Tunnel corridor, which gives it slightly more exposure to cool marine air from the west. On a given summer afternoon, Lafayette might run 3 to 5 degrees cooler than Walnut Creek, though you would need to be paying attention to notice. Walnut Creek lands in the middle: warm enough to be reliably sunny and hot in summer, sheltered enough from marine influence to stay dry and clear, but not as extreme as Concord on the hottest days. For outdoor activities with more tree cover, Briones Regional Park sits between these communities and tends to run a few degrees cooler than the town centers thanks to elevation and vegetation. If you are trying to chase the warmest or coolest option among nearby destinations, these micro-differences are the deciding factor.

It has four seasons, though they do not all arrive with equal force. Summer is long and dominant, stretching from May into October with minimal rain and consistent heat. This is the most distinctive season here: clear skies, warm afternoons, and that golden dry-grass look on the surrounding hills. Spring arrives quickly, usually by mid-February, when almond and cherry trees bloom and temperatures start climbing from winter lows. The data shows March 2025 posting a comfort score of 89 with highs around 71°F, which tells you spring is not just a brief transition but a genuine season in its own right. Fall is the most variable. September can still feel like summer (comfort score of 88 in September 2025), while November drops sharply (comfort score of 64 in November 2025). October is the turning point where you can get a perfect warm afternoon or a cold fog-soaked morning within the same week. Winter is mild by national standards but noticeably wet and gray compared to the rest of the year. December through February see the most rain and the lowest sunshine hours, around 6 to 7 hours per day. Cold snaps exist but snow in town is essentially unheard of. For a broader look at how Bay Area seasons work, Bay Area four seasons explains the regional patterns.