What is a microclimate?
People talk about the weather as what is happening now in terms of temperature, humidity, precipitation, wind, etc. Climate can be considered the average weather. That is, the weather over a long period of time is the climate. Microclimates are small regions with their own distinct weather patterns over time.
In most places in the world if the current weather is, say, 70 degrees and sunny with 10 mph winds from the south then if you go 50 miles in any direction it will be about the same. Within Sonoma County you can go 5 miles and have a distinct change in the weather. This is most pronounced during the warmer season, about May through October.
Sonoma County is a Mediterranean Climate with relatively mild, wet winters and warm dry summers. These are the only two real seasons. So it's dry and sunny during a large part of the year (during the grape growing season). Sonoma County would be much warmer if it wasn't for the cool waters of the Pacific Ocean lapping at its western shore. This means you have hot, dry air over the interior meeting up with cooler, moister, and heavier air over the ocean. With the coastal hills you have areas that get more influence from the cold waters and areas with much less.
Some average high and low temps in Sonoma County for July 1st:
Santa Rosa 82 / 53, Cloverdale 92 / 57, Bodega Bay 63 / 52.
Not many places have this sort of "weather diversity."
What does this mean for grape growing?
The two biggest natural influences for wine grape growing are the weather and the soil. With the past volcanic activity, seismic activity, the ocean, river valleys, and mountains there is an amazing array of different soil types in the county--more than in all of France.
Some grapes like more heat, such as Cabernet and Zinfandel, some like less, such as Chardonnay and Pinot Noir. Sonoma County is home to a high variety of premium wine grapes because everything can be grown successfully somewhere in the county. There aren't many places outside of certain parts of coastal California that can say this.
The other thing making Sonoma County's climate special is the warm, dry, sunny days followed by cool nights. "Warm, sunny, dry" is required for optimum grape growing. Too cold and the grapes won't ripen. Too hot and you get ripe red fruit, but lower acids (you need both in balance). Wet weather is bad because of mold issues. A dry growing season is ideal and most of California has that. "Cool nights" along with the warm days maintains that acidity and helps with flavor development. This is a reason people like mountains to grow grapes as you get cooler nights (and days) at higher elevations.
Sonoma County is a special place for wine grape growing.
|Low clouds (aka ocean fog) are a common sight|
Warmer and cooler microclimates and warm days with cool nights should tell you to pack so you can dress in layers. Bringing shorts, t-shirts, and sandals only isn't going to work. In the summer have clothes for 55 degrees and 90 degrees because you're likely to see both -- in the same day!