Saving Water Partnership

The Current Irrigation Index is:

Use the current Irrigation Index for the Seattle area to adjust your water schedule with the “Percent Adjust” or “Water Budgeting” feature found on most modern sprinkler controllers.

The Index is a percent of the typical "peak" watering period, when days are longest and weather is hottest (and the Index is 100%). The percentage is adjusted daily based on actual weather conditions.

The Weekly Watering Forecast is:

The Weekly Watering Forecast lets you adjust your watering schedule for the coming week. It updates itself every Sunday at 1:00 am. This percentage can then be programmed into your automatic irrigation controller. This forecasted index is based on the actual ET of the previous week combined with a forecasted increase based on average conditions from past years data.

Get Email Updates for the Irrigation Index  
Get daily updates when the Irrigation Index changes, and/or get weekly updates of the watering forecast:
Email:
Daily Irrigation Index update
weekly Watering Forecast Update
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Get up-to-date weather data

Find out how much water your lawn needs in real time! Get irrigation requirements and see up-to-date weather data for your area from the Puget Sound Weather Stations.

Calculate how much to irrigate your landscape

Use the Water Budget Calculator to determine how much water a lawn needs, based on the size of your irrigated landscape and yearly weather averages for the Seattle area.
Use the Sprinkler Scheduler to create watering schedules for automatic in-ground irrigation systems, based on the types of your plantings and watering system.

Yesterday’s ET in the Seattle area: 0.03"

ET (Evapotranspiration Rate) is how much water your plants use—thus, how much water you need to replace to keep your landscape green. Watering more than this is a waste of money and water.

Raw Data

Users who need access to weekly raw ET/rainfall data in CSV format can download the data by clicking here.

Please note:
irrigation is not needed in the Seattle area during the months of October through March.
Average ET, Actual and Effective Rainfall and Irrigation Index (for the irrigation season)
Month ET Actual Rainfall Eff. Rainfall (33%) Irrigation Index
April 2.38 2.87 0.89 53%
May 3.14 2.60 0.86 70%
June 3.50 2.00 0.66 78%
July 4.46 0.52 0.17 100%
August 3.71 1.11 0.37 83%
September 2.54 1.29 0.43 57%
Totals 19.73 10.24 3.38  


* Note
As with most technology, weather stations and the technology that ties it all together, are sometimes victims of malfunctions. Occasionally the weather data produced and posted on this site might be temporarily inaccurate. Please check the data being used for obvious errors. (for example: if the ET one day is .13" and the next it is 300" then caution is advised)