There are many diverse wine growing regions in Sonoma County. Each has a unique climate and geography. From warm, sunny days to cooler, fog covered valley floors, the variations in the geography and climate influence each individual region in many ways. Valleys, plains, mountaintops, forests, riverbeds and ocean cliffs create a unique geographical palette resulting in a staggering number of microclimates: trying to find one uniform characteristic to sum up Sonoma County geography is a challenge. There are, however, a few noteworthy features that influence the winegrowing regions of Sonoma County. Long before vineyards covered the land, Sonoma County was an inland sea. Tectonic upheavals of the coastal plates created the present day Mayacamas Mountains that form the eastern boundary of the county and created a soil structure in these areas defined by ash and lava. In addition to this rare distinction, Sonoma County is also home to more soil types than are found in all of France, creating a unique patchwork of site, soil and geographic rarities unlike any other region in the world.
Most wine regions benefit from proximity to a body of water, and for Sonoma County it’s the Russian River and the 60 miles of oceanic coastline. Meandering through a lush valley of vineyards, the rolling Russian River provides a conduit for pulling fog through Healdsburg and into the Alexander Valley. On the west side of the county, the Russian River continues its run through Green Valley and empties into the ocean at Jenner.
Sonoma County is heavily influenced by its close proximity to nearly 60 miles of Pacific Coast shoreline, and its cool nights and temperate days create the perfect conditions to draw in layers of oceanic fog to chill Sonoma’s warm interior valleys. Daytime temperatures average a comfortable 21˚C, with the warmest summer days rarely topping 28˚C. Night-time temperatures stay mostly in the single digits, meaning hard frosts are a rarity, even during critical flowering time for grapes. At the start of fall harvest, the weather remains moderate with little to no rainfall. Sonoma County experiences no measurable snow or hail and normal rainfall is moderate each year.
Grapes thrive in this climate and, while Sonoma County does experience occasional temperature extremes and hard rains, the reliably moderate diurnal swings are tempered by coastal fog and only trace amounts of summer rain. Grapes thrive there.