WSU CAHNRS

WSU Viticulture and Enology

Research and Extension

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

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.

Graphs are updated every 7-10 business days during the growing season; if you are not seeing updated numbers, please clear your browser cache.

AVA AgWeatherNet Station Cumulative GDD
April 1-July 23, 2017
(°F / °C)
Cumulative Precipitation
Jan 1 -July 23, 2017
(in / mm)
Red Mountain Benton City 1732/962 5.9/150
Wahluke Slope Mattawa 1575/875 3.8/97
Horse Heaven Hills Paterson 1615/897 3.8/97
Rattlesnake Hills Outlook 1464/813 4.7/118
Walla Walla Valley Walla Walla 1515/841 12.4/314
Yakima Valley WSU Headquarters 1393/774 5.9/149
Puget Sound Mt. Vernon 824/458 16.1/409
Columbia Gorge Mary Hill 1551/861 5.1/130
Lake Chelan Chelan South 1529/849 8.4/213
Snipes Mountain Port of Sunnyside 1413/785 6.2/158
Naches Heights Naches 1234/685 7.4/188
Ancient Lakes George West 1543/857 4.6/116
Rocks College Place 1462/812 9.9/251

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:

GDD Equation

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

 

2017 Cumulative GDD – Yakima Valley (WSU)

Graphs are updated on a  7 -10 business day  basis during the growing season. If you are not seeing an updated graph, please clear your browser cache. For GDD values for other locations in the state please visit AgWeatherNet .

 

Long-Term Average Cumulative GDD – All AVAs

2016 Cumulative GDD – All AVAs


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