A very important factor that accounts for the unique weather pattern of specific vineyards along the coast is topography. The topography of the coast effects what happens to the cool air as unobstructed prevailing winds push the cool air inland. Mountains perpendicular to the prevailing direction of air flow prevent the penetration of the low level cool air mass: being heavier, it does not get pushed up and over vertical obstructions. So even if you are right on the coast you may have temperatures warm enough to grow grapes since your vineyard juts high into the warmer top layers of air mass – remember, the higher the vineyard, the warmer the climate in this instance. Interestingly, the cool bottom layer continues to move laterally up east-west breaks in ridges created by rivers and streams, as is the case in the Russian River. As you might expect, there is a limit to the extent of cooling due to inland penetration, as travel over the land mass will gradually warm the air in the summer.
Fog is the final component that comes with the coastal cool air mass and adds a twist to the equation. A little bit is good as it moderates temperatures, but too much can increase the likelihood of fruit spoilage due to mold and mildew and may lead to too little heat to ripen grapes. And no fog might be an indicator of too little cooling air resulting in warm, short growing seasons less ideal for high quality winegrowing.
So you can see, as you analyze specific regions of the coast things get more complicated; definitions of the borders of climate zones become fuzzier and quite irregular. Phenomena to consider are breaks in the coastal ridges from east-west rivers, the height of north-south coastal ridges and the vineyard’s placement on the inverted triangle of cool air from the northern current. These factors direct and disrupt the even flow of heating air and create a multitude of microclimates that are further defined as specific appellations in the winegrowing world.