Snowpack, Streamflow and Water Resources This Summer

A number of people have asked about the water situation this summer, both in terms of water resources for agriculture and drinking, as well as the potential for wildfires.

At this point, the situation seems nominal:  relatively close to normal.

First, consider snowpack.  On April 1st, the snowpack water content over the region was very close to normal over the mountains of the Pacific Northwest. 

What about the long-term trend?    To answer that question, here is a plot of the NW snowpack on April 1st from 1984 to today prepared by UW atmospheric research scientist, Mark Albright.  The yearly values are shown by the blue line, a five-year running average by pink, and the overall trend is shown by the orange line.   Last few years have been near normal and there is only the slightest downward trend (which is not statistically significant).

After a dry period in April and very warm temperatures last week, there was considerable melt of the snowpack.   Snowpack amounts measured today were generally a bit below normal, and ranged from above normal for south Puget Sound (104%) to 58% for the upper Yakima basin.  The average is about 87%.

With the warm temperatures, a lot of melt water has surged into the regional rivers, with a number of major rivers running above normal and a few at flood stage (see below).  This is normal for our region.

So what about the future?  Let's start by looking at the reservoir levels for the Yakima system, which is critical for important east-side agriculture (see below).

  Actually quite good.   Water levels are slightly above average and the current storage is higher than the maximum storage of last year.  The Yakima system should be able to supply the water required.

Seattle's situation is even better, with current reservoir levels well in excess of normal (see below).

Looking forward, the best long-term precipitation forecast is available from the European Center.  Here is its 46 day forecast (through June 26) for the precipitation anomaly--the difference from normal.   This forecast suggests we will be wetter than normal during the period:  by up to an inch over Washington, to 2-4 inches over western Oregon and northwest California.  This pattern is particularly good because northern CA and southern Oregon has been drier than normal.

Finally, the forecast river flow for the region in early September provided by the National Weather Service River Forecast Center in Portland is for normal flows over Washington and northern Idaho.  But they are predicting lower than normal flow over southern Idaho and southeastern Oregon.

The bottom line of all this (and more I did not show) is that Washington State is in good shape regarding water for this summer.   There should be plenty of water for human and agricultural use and there is no reason to expect a worse than normal summer wildfire season this year. 

Considering what we are going through with the coronavirus, it would be good not to deal with extensive wildfires this summer.