San Ramon Weather

May is the single best month to visit San Ramon. The data backs this up clearly: May 2025 averaged a high of 73.4F, a low of 50.4F, a comfort score of 91 out of 100, and logged 12.6 hours of sunshine per day with zero recorded rainfall. That combination of warmth, long days, and dry skies is about as good as it gets in the Bay Area. April is a close second, with a 90 comfort score and only a third of an inch of rain. July is also excellent if you prefer slightly warmer temperatures, averaging highs in the high 70s and a comfort score of 89 to 90. The window from April through September is reliably good, with San Ramon earning comfort scores of 86 or higher every month in that stretch. If you want the peak of peak, though, book May. You will almost certainly get a warm, cloudless, breezy afternoon with no fog to speak of and no rain gear required.

San Ramon gets genuinely warm in summer, which is one of its main draws compared to the foggy Bay Area coast. June through August typically sees afternoon highs in the upper 70s to low 80s Fahrenheit. June 2024 averaged a high of 81.2F, while July 2024 came in at 78.1F and August 2024 at 80.1F. Those are comfortable warm-weather temperatures, not oppressive heat. Mornings stay mild, typically in the mid-50s, so the diurnal swing is noticeable but not extreme. San Ramon sits inland from the coast and is mostly sheltered from the marine layer that keeps San Francisco and the Peninsula cool all summer. This is why a town 30 miles from the coast can hit 80F on a July afternoon while San Francisco is stuck in the low 60s and fog. Occasional heat waves push temperatures into the 90s or even 100F, but those are multi-day events rather than the norm. For context on why inland areas heat up so much more than the coast, see why Bay Area microclimates create such dramatic temperature differences.

San Ramon gets morning fog, but it is a different animal from what you experience in San Francisco or along the coast. The data shows an average of about 2.1 hours of morning fog per day across the year, which is fairly modest. Summer months are actually among the clearest: June and July 2024 averaged only 1.8 to 1.9 hours of fog per day. Spring tends to bring slightly more fog, with March 2025 logging 2.8 hours. Because San Ramon sits in the Tri-Valley, roughly sheltered from the direct marine push by the hills and ridges to the west, the marine layer usually burns off before midday. By late morning on most summer days, you have full sunshine and temperatures climbing toward the afternoon high. This is a meaningful difference from coastal communities where the fog can persist into mid-afternoon. If you want to understand why the Bay Area fog behaves the way it does, this explanation of morning fog formation is worth reading. Nearby Las Trampas Regional Wilderness sits in the hills above San Ramon and sometimes clears fog even earlier due to elevation.

San Ramon's rainy season runs from November through March, following the Mediterranean climate pattern of the broader Bay Area. January is the wettest month on record in this dataset, with 6.6 inches of rain in January 2025. November and February are also legitimately wet, each logging between 4.7 and 5.9 inches. The driest stretch is late spring through summer: May 2025 had zero measurable rainfall, June averaged under a tenth of an inch, and July and August together logged under half an inch. With approximately 77 rainy days per year, San Ramon is drier than the North Bay but wetter than the South Bay. The important thing to know about Bay Area rain is that it tends to come in discrete storm systems, often followed by brilliant clear days. A wet week in January does not mean the whole month is a washout. For more context on which month is typically the rainiest in the Bay Area, the pattern at San Ramon tracks closely with other inland Contra Costa towns.

San Ramon and Danville share nearly identical weather because they sit right next to each other in the San Ramon Valley. Both are inland, both are mostly sheltered from the marine layer, and both trend warmer and sunnier than the coastal Bay Area. If there is any difference at all, it is likely within the margin of error of a weather station. What you will find in both towns is the inland Contra Costa pattern: warm summer afternoons in the 75 to 82F range, mild mornings in the low 50s, minimal fog, and a dry season that stretches from May through September. Where San Ramon and Danville differ more meaningfully from nearby locations is when you compare them to Dublin to the south, which sits at the mouth of the valley and catches slightly more wind off the bay, or to the regional parks in the hills, which can be cooler due to elevation and exposure. For most practical purposes, if you know the weather in Danville, you know the weather in San Ramon.

San Ramon is one of the better places in the Bay Area for outdoor dining across a wide stretch of the year. From April through October, afternoon temperatures range from the low 70s to low 80s Fahrenheit with low humidity and, on most days, light winds. A comfort score that sits at 86 or above from March through September tells you that conditions are genuinely pleasant, not just tolerable. Summer evenings cool down into the mid-50s, so a light jacket is smart for dinner once the sun drops. November and December push average highs into the upper 50s, which is jacket weather for most people, and rain becomes a real possibility. January is the toughest month for outdoor dining, with highs only reaching the high 50s and January 2025 logging 6.6 inches of rain. The sweet spot for reliable outdoor comfort at a restaurant patio is May through early October. Spring is actually underrated for this: April and May have some of the year's best comfort scores and daylight is still lengthening, so evening dinners before 8 PM get full sun.

The right packing strategy for San Ramon depends a lot on the time of year. In summer (June through September), you can lean warm: light shirts, shorts, and sunglasses are appropriate for afternoon activities when highs reach the high 70s to low 80s. But mornings start in the low to mid-50s, so if you are going out early, bring a light layer. Sunscreen is non-negotiable even on slightly overcast days, and a hat helps in the afternoon heat. In spring and fall (March to May, October to November), layers are the right call. Afternoons can be genuinely warm, but mornings and evenings are noticeably cooler, and a fleece or light jacket will get used. In winter (December through February), treat it like cool weather: a real jacket, possibly a waterproof shell, and layers underneath. Rain gear is worth having from November through March. One thing San Ramon does not typically require is the heavy windbreaker that is essential near the coast. The town is sheltered enough that wind is rarely a dominant factor, unlike Anthony Chabot Regional Park or the ridgelines to the west.

This is a real phenomenon and worth understanding if you are planning a fall visit. September 2024 averaged a high of 79F with a comfort score of 86. July 2024, which you might expect to be the hottest month, averaged a high of 78.1F. September often rivals or beats July in the inland Bay Area because the marine layer weakens as summer progresses, the fog season winds down, and the regional pressure patterns shift in ways that allow more onshore heating. The inland valleys, including San Ramon, can see some of their hottest individual days in September and October. This is counterintuitive if you are used to continental climates where summer peaks in July. The Bay Area has its own rhythm. There is a detailed explanation of this pattern at why September is often hotter than July in the Bay Area. For visitors, the practical implication is that early fall is not cool-down season in San Ramon. It can still be warm enough for outdoor activities, lighter clothing, and high comfort scores well into October.

San Ramon's winters are mild by most standards but noticeably cooler than summer. January 2025 averaged a high of 59.4F and a low of 41.4F, and December 2024 came in at a high of 58.7F with a low of 37.4F. Those low temperatures mean frost is possible on clear, calm nights, especially in low-lying areas. The comfort score drops to its annual lows in winter: December 2025 scored a 70 and January 2025 scored a 75. Sunshine averages about 6.5 to 7 hours per day in December and January, versus 12 or more hours in May and June. Snow is essentially nonexistent at San Ramon's 394-foot elevation, though you might catch a dusting on Mt. Diablo on the rare exceptionally cold winter day. Mt. Diablo Summit, at nearly 3,900 feet, can see significant temperature differences from the valley below. San Ramon's winters are better described as cool and occasionally rainy rather than harsh or punishing. Outdoor activities remain reasonable on dry days; just plan for shorter usable hours before and after the cold drops in.

San Ramon averages about 9.4 hours of sunshine per day across the full year, and the data suggests roughly 275 days per year qualify as what most people would call a good or excellent weather day. The sunniest months are May and June, when daily sunshine averages 12.4 and 12.2 hours respectively. July and August still log 10 to 11 hours of sunshine per day despite being the core of the summer fog season on the coast. The least sunny months are November through January, where daily sunshine dips to around 6.5 to 6.7 hours. Even in those months, San Ramon is frequently sunnier than coastal communities because the marine layer does not penetrate as far inland. This is the fundamental trade the inland valleys make: more warmth and more sunshine in exchange for hotter occasional heat waves and cooler, frostier winter nights compared to the thermally moderate coast. For most Bay Area visitors seeking reliable sun, San Ramon is among the more dependable choices in the region.