The Puget Sound AVA is a part of meso-climate region that stretches from British Columbia to northern California called Cascadia. It is greatly influenced by the Pacific Ocean and Puget Sound. The climate of the Puget Sound region is officially called a Maritime climate. All that means is that the ocean greatly influences what happens in the Puget Sound basin it keeps our summers cool and are winter cool but mild. Western WA state is classified in the same climate zone as most of England, France and norther Spain. Maritime climates are a mix of Mediterranean and Continental climates. Mediterranean climates are usually hot in the summer and mild in the winter and dry. Continental climates are hot in the summer and bitterly cold in the winter, with snow and subzero temperatures. The proximity to the Pacific Ocean and the water from the Sound in the Puget Sound basin keeps things mild all year long.
On average, SeaTac Airport has about 2050 Growing Degree Days (GDDs) (WRCC 2009) and 37″ of rain annually. In the Puget Sound, this is good benchmark to start from since it seems to fall in between the warmer southern and the cooler northern ones and rainfall is pretty typical of the lowland areas. There will be variations in your local micro-climate that will dictate what you can grow at your location. Elevation and distance from the Puget Sound play a huge part in what your temperatures are.
Generally, the Puget Sound basin receives most of its annual rainfall in the wintertime. November is generally the wettest month, followed by December and January. June, July and August are the driest months. Storms in the winter move off the Pacific into the Puget Sound bringing about 80% of the rain in a 6-month period. Most of the Puget Sound receives some “rain shadowing” from the Olympic Mountains during storms, although in the central Puget Sound area, a “convergence zone” will set up and dump larger amounts of precipitation. This zone can move around, but generally it’s in Snohomish county and northern King County. Summers are dry and mild with temperatures rarely going above 90 degrees. In fact it can be so dry in the summer that drip irrigation is recommended in most vineyards for the first couple of years.
Growing Degree Days
In the grape growing industry, we use a common system of measuring accumulated heat during the growing season. We call this Growing Degree Days. This makes it easy to compare different growing regions around the world and also to explore new areas and see what might grow well in a particular area. It is used for a variety of crops.
Growing Degree Days (GDD) is a system of determining how hot an area is based on certain threshold temperatures. Grapes are based on 50F (10C) degrees. Generally, grapes don’t have any growth at temperatures under 50 and above 90.
To calculate GDDs you need a weather station or find your closest official weather station. GDDs are typically calculated (In the Northern Hemisphere) from April 1st to October 31st. Every day you record the high and the low temperatures and average them out. If the average is above 50f degrees then you minus 50 from the average and the remainder is the GDDs for that day. If the average is below 50, you just put a 0 as the number. No negative numbers. You will take all of those daily degree numbers and add them up for the whole season.
For example, a day with a high of 65 °F and a low of 40 °F (and a base of 50 °F) would contribute 7.5 GDDs.
A day with a high of 45 °F and a low of 20 °F (and a base of 50 °C) would contribute 0 (zero) GDDs. Grapes need about a minimum of 1500 degree days for a whole season to ripen, but that varies from grape to grape and only the very earliest ripening grapes will mature in 1500 degree days. Grapes the ripen at 1500 GDD are generally obscure grapes and sometimes don’t make quality wine. Starting at about 1700 degree days, you can make quality wine from a few selected grapes. As the heat gets closer to 2000 GDDs high quality wine can be made from well known grape varieties. As a comparison, Cabernet Sauvignon needs about a minimum of 2400 degree days to ripen. The Puget Sound region averages between 1600-2000 GDDs depending on where you are located. We will talk more about variety selection in the the grape variety selection page. Most of the Willamette Valley gets about 2200 degree days and can sometimes ripen Cabernet, Syrah and Riesling. We have a very similar climate to western Oregon, but a bit cooler.
When we look at the GDDs around the world a good comparison in Europe to the Puget Sound might be the Loire valley, near Nantes (Muscadet), Champagne or Chablis in the northern part of Burgundy. Chardonnay is a stretch for us here in the Puget Sound region. Most pinot noir will ripen in most years. Riesling, as far as I’ve seen, will not ripen in the Puget Sound AVA.
Another method to predict what might ripen in the Puget Sound AVA is a simple calculation. The total average temperature during the growing season. The Puget Sound region averages between 56-59 degrees. This fall directly across several well known grape varieties from Europe, Pinot Gris, Pinot Noir, Chardonnay and Sauvignon Blanc.
But, the Puget Sound region is warming up just like the rest of the world. Tracking GDDs for decades shows a clearly upward swing in temperatures. Conversations with older growers and even in my own experience have show that grapes like pinot noir hardly ever ripened in the 1970s or earlier. Some of that may have to do with the clones and rootstocks we now have available to us and also better training and growing practices. It will be a long time before the Puget Sound region can make the jump to the next group of grapes like Cab Franc and Dolcetto to ripen in the Puget Sound. Pinot Noir will be the future for growing here for many decades.