Mill Valley Weather

April 2025 stands out as the best month to visit Mill Valley, with a comfort score of 91/100, afternoon highs around 72°F, and nearly 13 hours of daily sunshine. July is your other excellent choice, offering similar comfort (91/100) with slightly warmer temperatures around 76°F and minimal morning fog (1.6 hours). Both months provide ideal conditions for exploring the town's upscale dining scene and hiking trails around Mt. Tam without layers of fog or rain. If you prefer slightly cooler but still pleasant weather, May and June are strong alternatives with comfort scores in the mid-80s and abundant sunshine.

Mill Valley experiences moderate morning fog, averaging 2.2 hours per day across the year. Summer months (June through September) are your best bet if you want to minimize fog, with July showing the least at just 1.6 hours in the morning. By contrast, October through December brings thicker fog, peaking in November at 4.2 hours daily as marine layer activity increases. April is almost fog-free (0.4 hours), which helps explain why it's such a popular travel month. If you're planning outdoor dining or early hikes, summer visits give you clearer mornings, while you'll want to wait past mid-morning in winter months. For more details on how Bay Area fog forms, this article explains the coastal dynamics.

Mill Valley reaches pleasant outdoor dining temperatures most of the year. Summer highs (June through August) hover in the low to mid-70s°F, which is ideal for alfresco meals without feeling too warm. April and July push into the upper 70s, offering warm-but-not-hot conditions. Fall and spring temperatures in the 60s to low 70s are perfect for sidewalk tables when the sun is out. The town's elevation of 52 feet and proximity to Mt. Tam means you'll feel occasional cool breezes, but afternoon conditions are almost always comfortable. Only winter months (November through February) dip below 60°F regularly. The real challenge isn't heat but fog and cloud cover, especially in winter. With a year-round comfort score averaging 82/100, Mill Valley is consistently pleasant for outdoor activities and dining compared to many other Bay Area towns.

Mill Valley's rainy season runs from October through March, with peak rainfall in November (6.4 inches) and January (6.51 inches). October brings a sharp transition with 3.28 inches, signaling the shift from dry summer. December and February are also notably wet months. The summer months (June through August) are essentially rain-free, with virtually no precipitation and clear skies ideal for hiking and outdoor pursuits. April and May see minimal rain (0.1 and 0 inches) despite being the most comfortable months overall. Spring (March through May) strikes a balance: some rain in March (0.5 inches) but increasingly dry conditions as you head toward summer. If you're visiting to hike trails around Mt. Tam or dine outdoors, aim for April through September when dry conditions prevail. Learn more about Bay Area's rainy patterns here.

April through May and July through September provide the best hiking weather in Mill Valley. April is particularly exceptional, with 12.8 hours of daily sunshine, comfortable 72°F afternoons, virtually no morning fog, and minimal rain. July and August bring the most consistent dry conditions and warm afternoons (around 75-76°F), though occasional August rain is possible. May and June stay dry and sunny despite slightly cooler afternoons. Fall through early spring presents challenges: November through January are wet, muddy, and gray, while October can still bring significant rain (3.28 inches) that makes trails slick. Late February and March show promise as conditions dry out and sunshine increases to 9-11 hours daily. Best months for Bay Area hiking are detailed here. Pack layers regardless of season, as Mt. Tam's elevation creates cooler conditions than the town itself.

Mill Valley sits at the base of Mt. Tamalpais and is generally slightly cooler than lower-elevation neighbors like Larkspur due to proximity to marine influences and higher elevation (52 feet). The temperature differential is modest, typically 2-3°F, most noticeable in summer. Both towns experience similar fog patterns in morning hours, though Mill Valley's elevation exposes it to more wind channeling down Mt. Tam. Larkspur tends to warm up slightly faster in afternoon, while Mill Valley stays more temperate. The microclimate differences are subtle for day-to-day planning. Corte Madera, slightly south and lower, will be marginally warmer year-round. For the most dramatic climate differences in Marin, compare Mill Valley to higher peaks like Mt. Tam East Peak or lower valley towns. Understanding these variations helps you choose the right destination based on your comfort preferences.

Pack in layers, always. Even on warm summer afternoons (mid-70s), morning fog and Mt. Tam's wind can make it feel 10-15°F cooler. Bring a light jacket or fleece for morning hikes and outdoor meals, which you'll shed by noon most days. From June through August, shorts and a t-shirt work during the day, but keep that jacket handy for evening dining or altitude changes. Spring and fall require more versatility: long pants or jeans, a sweater, and windproof outer layer. Winter visits (November through February) demand heavier layers, waterproof jacket, and comfortable walking shoes since rain is frequent and trails can be muddy. A hat helps with sun protection despite morning fog, as UV index climbs quickly once fog burns off. Don't overpack heavy winter gear even in December and January, as highs still reach mid-to-upper 50s. This article on layer dressing explains why the Bay Area demands this approach.

Mill Valley averages 9.4 hours of daily sunshine annually, with dramatic seasonal variation. Summer peaks around 11-13 hours daily from April through July, with July hitting 11.7 hours. August begins a gradual decline to 10 hours, then falls to single-digit hours by October (7.2 hours) and winter (6-7 hours November through January). Late winter and spring show rapid improvement: February bounces back to 9.1 hours, March reaches 11.1, and April explodes to 12.8 hours. This sunshine pattern explains why April feels so energizing compared to winter months. The town gets reasonable sun even in rainy winter, thanks to afternoon breaks between storms. Autumn (September and October) provide a comfortable transition with 8-9 hours daily and still-pleasant temperatures. Plan indoor activities like dining and arts venues for November through February when fog lingers longer and sunshine is limited, reserving outdoor days for April through September.

Mill Valley has a distinct dry season from roughly June through April, with virtually no rain during this eight-month stretch. Summer months (June, July, August) are almost entirely rain-free, averaging just 0.06 inches combined across three months. April hits zero inches while May, March, and February show minimal precipitation. October marks the transition with 3.28 inches, then November explodes into the wettest month (6.4 inches), leading into a rainy winter. December and January each deliver over 3 inches, though winter rain tends to come in bursts between dry spells rather than constant drizzle. The rainy season (October through March) accounts for about 90 percent of annual precipitation. With roughly 71 rainy days per year, you'll encounter wet weather, but many days still see partial sun or breaks between storms. Visit between May and September for essentially guaranteed dry conditions, or plan winter visits around weather forecasts for clearer windows.

Mill Valley at 52 feet elevation enjoys significantly warmer and more stable weather than Mt. Tam's higher elevations. As you climb Mt. Tamalpais toward East Peak, expect temperatures to drop roughly 3-4°F per 1,000 feet, making the summit 10-15°F cooler than town. Wind also intensifies with elevation, and fog lingers much longer on the ridges and upper slopes, sometimes trapping the peak in clouds while town enjoys afternoon sun. Morning fog at sea level might clear by 10 a.m., while it can persist most of the day higher up. Winter weather becomes increasingly severe at elevation, with potential snow or ice on upper slopes while Mill Valley stays above freezing. Conversely, summer heat that might feel uncomfortable in town (mid-70s) becomes pleasant and cool on the mountain. For comfortable day hikes on Mt. Tam, start early from Mill Valley and plan to be above the fog by mid-morning. Explore Mount Tamalpais State Park for comparison weather data.

December in Mill Valley is cool, wet, and gray, with average highs around 56°F and lows near 47°F. The month sees 3.17 inches of rain spread across multiple rainy days, so expect to encounter wet weather at least part of your visit. Mornings feature 2.3 hours of fog on average, and daily sunshine averages just 6.2 hours. Plan indoor activities: the town's excellent dining and arts scene become primary attractions rather than outdoor dining and hiking. That said, December isn't relentlessly dark. Many days break clear in afternoon with pale winter sunlight and dramatic cloud formations. Bundle up for morning walks through town, bringing a waterproof jacket and layers. The comfort score of 66/100 is the year's lowest, reflecting winter's general challenge. If you must visit December, aim for the holiday season (mid to late December) which statistically has brief clearer windows. For better weather, shift your trip to late March or early April when conditions reverse dramatically, bringing sunshine and comfort scores approaching 90/100.