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Growing Degree Days

The progression of in-season grapevine development is strongly influenced by air temperature. As such, average heat accumulation is often used to compare regions and vine growing condition. This average heat accumulation is often referred to as Growing Degree Days (GDD). The summation of daily GDD units can be used for a variety of things: comparing one region to another, comparing one season to another, and predicting important stages in vine development (bloom, veraison, and maturity).

GDD units can be calculated in °F or °C; however, they result in different numbers so make sure that when you are comparing GDD units, you are comparing units with the same temperature scale. Washington State University calculates all GDD in °F, with a base temperature for grapes at 50 °F. Values in °C (with a base of 10°C) can be obtained as follows: GDD[°C]=5/9 x GDD[°F]. Cumulative GDD is a running total of GDD from April 1 through October 31.


Washington AVA Accumulated Growing Degree Days


You can update your own AVA-specific weather data by accessing the AgWeatherNet station associated with the AVA names below.


Below are the current-season cumulative GDD as calculated by AgWeatherNet. Clicking on the AVA name will open the seasonal GDD graph specific to the indicated weather station in that AVA. Since AVAs in WA can cover large areas, please visit  AgWeatherNet to view real-time GDD accumulation for other stations/locations within your desired AVA.


(AgWeatherNet Station)
Cumulative GDD
Apr 1 – October 31, 2023
(°F / °C)
Cumulative Precipitation
Jan 1 – October 31, 2023
(in / mm)
Red Mountain
3754/2085 4.6/117
Wahluke Slope
3528/1960 3.4/86
Horse Heaven Hills
3360/1867 2.3/58
Rattlesnake Hills
3408/1893 3.9/100
Walla Walla Valley
3275/1819 10.7/271
Yakima Valley
3259/1810 3.8/98
Puget Sound
1765/981 14.6/370
Columbia Gorge
3588/1993 5.3/136
Lake Chelan
3357/1865 8.14/207
Snipes Mountain
3228/1793 3.0/76
Naches Heights
2924/1624 6.4/162
Ancient Lakes
3404/1891 4.9/124
3136/1742 11.1/281
Royal Slope
(Royal Slope)
3408/1893 5.0/126
Candy Mountain
3819/2121 3.2/81
Lewis-Clark Valley
2322/1290 9.2/233


Calculating Your Own Growing Degree Days

GDD are calculated by subtracting 50 from the average daily temperature (°F). If the resulting value is less than 0, then it is set to 0. Thus, daily GDD units are always positive.

This is the GDD equation that is used to calculate daily GDD units:

AgWeatherNet is the Washington Agricultural Weather Network and can be used to monitor temperatures, precipitation, pan evaporation, and other parameters at weather stations at over 130 locations in Washington. Conditions in your vineyard may vary depending on the vineyard’s mesoclimate. If you have a weather station in or near your vineyard, you can calculate your own GDD.

To observe your own GDD accumulation for a specific station not listed below, go to AgWeatherNet, sign into your free account, click on “AWN Reports” on the left screen, and select your station and units. Click “Submit”, then click “Degree Day” on the left, then select 50°F as your base temperature with no upper threshold, then click “Submit”.

Growing Degree Day Charts for Washington


2023 Cumulative GDD – Yakima Valley (WSU)

2022 Cumulative GDD – All AVAs

     Long term Cumulative GDD – All AVAs