This episode is about how “North Coast” isn’t a style, it’s an umbrella — and the only way to make it make sense is to follow the physical forces that shape temperature, ripening pace, and fruit concentration: ocean, fog corridors, altitude, mountain shadows, and the way valleys act like funnels. Mendocino shows the cleanest contrast: close-to-coast AVAs like Anderson Valley behave like cool-climate systems because fog and cold air are pulled inland along the Navarro River, stretching the day’s temperature swing and slowing sugar accumulation, which is why Pinot Noir and Chardonnay can hold acidity and still reach flavor ripeness. Move inland or climb to warmer pockets and the grapes shift with the heat: Zinfandel, Syrah, Petite Sirah and Cabernet Sauvignon become viable, and the county’s lower grape prices explain why so much of this fruit ends up supporting multi-regional blends.
Lake County is the flip side of the same map logic: it’s warm because it sits in a rain shadow, but it doesn’t simply become “hot” because Clear Lake and altitude create afternoon breezes and cooler nights that can preserve freshness, which is why Cabernet Sauvignon and Sauvignon Blanc are so central here. The key business takeaway is that, despite some high-quality sites, a lot of Lake County still functions as a blending resource — fruit that lifts value elsewhere because it’s priced below Napa and Sonoma.
Then Sonoma is where the episode tightens into exam-grade precision: three massive overlapping AVAs exist partly for commercial labelling and “estate bottled” practicality, but within them the real story is how specific corridors and barriers create distinct climates. Alexander Valley reads warm but gains evening cooling through regional air movement, shifting Cabernet from simply ripe to structured, and benchland altitude plus poorer soils push smaller berries and more tannin. Knights Valley shows what happens when shelter removes the ocean’s brake — heat drives full-bodied Cabernet unless altitude is used to claw back freshness. Dry Creek demonstrates how a warm valley can still retain acidity because cool fog and air are pulled in through gaps, and why that matters for Zinfandel styles from fresher to jammy depending on exposure and sub-zone. Rockpile is concentration-by-stress: above the fog, long sunshine hours, shallow soils, wind-driven evapotranspiration — low yields, ripe intensity, and a distinctive night-time warmth because the lake creates an inversion layer.
Russian River Valley is the fog lesson in its purest form: evening fog lowers temperatures, slows sugar build, protects acidity while flavors develop — which is why Pinot Noir and Chardonnay dominate the cooler south and west, and why the boundaries expanded as demand for that fog-influenced fruit grew. Green Valley pushes that cooling further for higher acidity and tighter fruit, while Chalk Hill flips warmer due to inland distance and topographic shelter, making it better suited to fuller styles. Sonoma Coast is exposure and limitation: wind and fog reduce sunshine and disrupt fruit set, so yields drop and early ripeners rule — but Fort Ross-Seaview shows how altitude above the fog can increase sunshine without losing the cooling influence of coastal winds. Petaluma Gap is the “wind as a ripening control” case study: persistent winds lower temperature and can close stomata, slowing photosynthesis, and that’s why the wines land with higher acidity and often lower alcohol. Finally, Sonoma Valley pulls in the bay effect: San Pablo Bay cools the southern end, while mountain sites above fog gain intense sun by day and cool nights by drainage air, which explains ripe tannins and retained acidity in Cabernet on Sonoma Mountain — and why Carneros became an early recognized cool zone for Pinot and Chardonnay, with labelling shaped by its county overlap.
In the D3 exam, this episode is a gift because it lets you score marks by doing what examiners actually reward: not naming AVAs, but explaining why the same grapes taste different across short distances, and linking those differences to price and positioning — blending fruit versus vineyard-specific bottlings, mid-priced versus super-premium, and the labelling rules that make “Sonoma County” and the overarching AVAs commercially meaningful.
Looking for all episodes in one place?
I’ve created an evergreen “Start Here” hub for this unit so you can access the full series without inbox overload.
You’ll find the complete list of episodes, organized in syllabus order, here:
https://thesommpour.substack.com/p/wset-diploma-d3-wines-of-the-world
