Why are Sonoma and Napa Wines Different?

The key factors in growing premium wine grapes are the microclimate and the soil. They impact the ripening and flavors, and define the characteristics of a wine. The microclimates and soils in Sonoma County are different from those in Napa, even though the two counties are side-by-side. Winemaking is also key to the properties of the finished wine, but we can assume equipment and practices are similar. 

So it's the microclimates and soils that make the wines different. Let's take a deeper dive into why the grapes coming into the winery can be different in these two neighbors.

 

Climate 

Temperatures, the day-to-night temperature swings, amount of sunlight, wind, and rainfall all matter. Different grape varieties prefer different climate characteristics. Too hot, too cold, too humid, and severe weather cause problems.

Cooler areas tend to produce light, crisp, and bright wines. Crisp and bright mean higher acidity. Chardonnay and Pinot Noir are best in cooler regions. Warmer regions mean big, bold, soft, and lush wines. Soft and lush mean lower acids. Too much heat means jammy and flabby wines because the fruit was too ripe and the acids too low.

Cabernet Sauvignon, for example, is a grape that prefers it warmer. Cab from a colder region will be leaner, have higher acid, less fruit flavor and more vegetative characteristics often described as bell pepper, eucalyptus, or mint.

A microclimate is just a small area where the climate is different from the surrounding area. This could mean it's warmer, cooler, cloudier, wetter, etc.

Soil

Soil types have different nutrients, will have different temperatures, and water retention. Well drained soils are better for healthy roots. Deep soils allow the roots to go deep for drought resistance. Nutrients and pH must be in balance for healthy vines and good grapes.

Sand, clay, limestone, and loam (a mix of sand, silt, clay) are found in vineyards; sometimes silt and volcanic soils. Each has a different effect on the wine.

Sonoma's Climate

The western border of the county is the Pacific Ocean. The current is from the Gulf of Alaska, so the water is chilly year around. Coast water temperatures are in the 50s year around in Northern California. There are several coastal mountain ranges that block the cool winds from the ocean to a greater or lesser degree in different parts of the county. 

The southern end of the county gets cool breezes from the San Pablo Bay, which is connected to the San Francisco Bay. Also, from the Pacific through what's known as the Petaluma Gap. In the mid-part of the county, the Russian River's path to the ocean also allows wind and fog to come through.

On a summer day, you can find a 50 degree range in air temps between the coolest and hottest places in the county. There are bigger mountains in the northern part of the county, so the farther inland and farther north you go, the warmer the growing season temperatures. These daytime temperatures cool significantly overnight. It's rare to find an overnight low above 60 degrees.

The warm, sunny days during the growing season along with the cool nights are perfect for premium wine grapes.

Visitors are often perplexed by the different weather in the county. As the locals say, dress in layers.

A low marine layer forms over the coast and moves inland overnight and into the morning. This is more pronounced near the water and in the southern part of the county. The chilly air coming off of the Pacific makes for a great growing area for cool climate grapes, such as Chardonnay and Pinot Noir, while protected inland areas grow Cabernet Sauvignon and Zinfandel, and other grapes.

The key to Sonoma County wine grapes is the cold Pacific water.

Napa's Climate

Cooling influences mostly come from the San Pablo Bay in the south. As you go up the valley, it gets hotter during the grape growing season. The valley is flanked on both sides by mountain ranges. Many of the vineyards are above the valley floor in areas such as Atlas Peak, Howell Mountain, and Spring Mountain. 

Calistoga is much warmer than the town of Napa, 25 miles to the south. Calistoga will cool drastically overnight, with daytime temps often reaching 95, then dropping to the low-50s overnight. Cabernet grapes love this weather.

Sonoma's Soil

The county has more soil types than France. Some examples are Gold Ridge (sandy, clay loam), volcanic, and ash (derived from ancient volcanoes). The topography that includes the coast, mountains with ancient volcanoes, many valleys, and the Russian River give us the diverse soils.
 

Napa's Soil

Napa also has many soil types with the mountains, the valley floor, plus volcanic and marine influences. Napa has nearly as many soil types as Sonoma.

Sonoma vs. Napa

Sonoma is most known for Pinot Noir, Napa for Cabernet, but you'll find a wide variety of grapes grown. Pinot has been a thing in Sonoma for about the past 25 years. If you go to mid-20th century, Napa was about Petite Sirah! 

In tons of grapes grown in Sonoma, Chardonnay is #1, Pinot Noir #2, Cab Sauv #3. In Napa, Cabernet Sauvignon is more than half of all the grapes, with Chardonnay and Merlot a distant #2 and #3.

Morning fog over Sonoma County
image from pressdemocrat.com

Sources

foodandwine.com
goodpairdays.com
sonomacounty.com