Washington AVA Growing Degree Days
The progression of grape phenological stages (sap flow, bud break, veraison, etc.) is strongly influenced by ambient temperature and so are vegetative growth and fruit ripening. The calculation of daily Growing Degree Days (GDD) is a tool that can be used to predict important stages such as bloom, veraison and crop maturity.
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.
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 GDD are always 0 or greater. GDD Equation:
We calculate all GDD in °F. Values in °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.
The following table shows a comparison of seasonal cumulative GDD and precipitation taken from AgWeatherNet stations in ten of the eleven American Viticultural Areas (AVA)s in Washington. Since the Columbia Valley AVA covers such a large area it is impossible to pick one representative weather station. Clicking on the AVA name will open the seasonal GDD graph specific to the chosen AVA.
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 50F as your base temperature with no upper threshold, then click “Submit”. The accumulated heat units are what you need!
| AVA | AgWeatherNet Station | CumulativeGDD Apr 1 -June 17, 2013 (°F / °C) |
Cumulative Precipitation
Jan 1 – June 17, 2013 in / mm) |
|---|---|---|---|
| Red Mountain | Benton City | 782/434 | 2.1/52 |
| Wahluke Slope | Mattawa | 792/440 | 2.1/53 |
| Horse Heaven Hills | Paterson | 773/430 | 2.5/63 |
| Rattlesnake Hills | Outlook | 740/411 | 2.5/63 |
| Walla Walla Valley | Walla Walla | 714/397 | 5.7/144 |
| Yakima Valley | WSU Headquarters | 694/386 | 2.4/62 |
| Puget Sound | Mt. Vernon | 358/199 | 16.6/422 |
| Columbia Gorge | Mary Hill | 777/432 | 2.8/71 |
| Lake Chelan | Chelan South | 715/397 | 4.6/118 |
| Snipes Mountain | Port of Sunnyside | 664/369 | 2.2/56 |
| Naches Heights | Naches | 584/324 | 2.6/66 |
| Ancient Lakes | George West | 750/417 | 1.3/34 |
2013 Cumulative GDD-Yakima Valley (WSU)
Long-Term Average Cumulative GDD-All AVAs
2012 Cumulative GDD-All AVAs
