Growing Degree Days

Here are the Growing Degree Days (GDDs) for SeaTac airport for the last 7 years. GDDs are an easy way to calculate how much heat has occured during a growing season. Starting April 1st and going to October 31st you take the high and low of each day and add them together, then divide by 2 and then minus 50 and anything above zero is recorded. Then we take all the GDDs for each day of the growing season and add them together.


70 + 50 = 120 / 2 = 60 - 50 = 10 GDDs

It's an easy way to find out how your site compares to others and also a good way to track how the current year is progressing compared to past years.

Here are some numbers for Seatac airport near Seattle:


Degree Days

57 year average














2004 2220

The blue line is the year to year GDDs.
The Black line is a regressive analysis trendline projected out 20 years to the year 2024.
The red line is the 57 year average of 2050 GDDs.

Comparison of Puget Sound Growing Regions

Location Degree Days

Comparison of Cool Climate growing Regions

District Degree Days* Grapes Grown
Chablis 1710 Chardonnay
Champagne 1890 Chardonnay, Pinot Meunier, Pinot Noir
Loire 1710-1980 Melon, Sauvignon Blanc, Chasselas, Cab Franc
Ahr 1620-1980 Pinot Noir, Riesling, Muller-Thurgau
Nahe 1980-2160 Muller-Thurgau, Riesling, Sylvaner
Alsace 2210 Chasselas, Sylvaner, Pinot Gris, Pinot Blanc, Gewurztraminer, Muscat, Riesling, Auxerrois, Pinot Noir
Cote d'Or 2120 Pinot Noir, Chardonnay
Medoc 2520 Cabernet Sauvignon, Merlot, Cabernet Franc
Puget Sound 1700-2200 Madeleine Angevine, Siegerrebe, Muller-Thurgau, Pinot Noir, Chardonnay, Pinot Gris
Willamette Valley 2200-2500 Pinot Noir, Chardonnay, Pinot Gris, Pinot Blanc, Riesling

*From "The Production of Grapes and Wine in Cool Climates", by Jackson and Schuster, except the U.S. districts.