Friday, February 22, 2019

Big gains in snowpack, but still below normal

If I were writing this blog two weeks ago, I’d be telling a very different story.

Before the infamous 2019 snowpocalypse hit, some of the state’s water supply experts were experiencing mild heartburn over the outlook of water supply for the year. We were at 74 percent of normal snowpack. That’s the seventh-lowest season of snowpack at that point in the past three decades. But then, to the dismay of school officials but the delight of water managers, Mother Nature decided to bring it on.

Big snow

We love snow at Ecology. It’s critical to our state's mountain snowpack that feeds our rivers and reservoirs and the majority of Washington's electricity is produced through hydropower. 

There was a huge amount of snow that landed across the Cascades. How big was our bump in snowpack? About twenty percent. A huge jump in just a few days, and for mid-February, unprecedented at some locations. 

The statewide average for snowpack is now at 91 percent of normal. If this were baseball, you could say we just had a five-run inning.  

We received so much snow the director of Ecology took to Twitter to share just how much  actually hit the slopes. It was massive. 

See the map she included. It illustrates just how much snow measured at various sites around the state. 

Snowpack is Washington’s largest reservoir

The National Snow Analysis estimates that, as of Feb. 20, Washington’s snowpack contains about 30 million acre feet of water. Eight million acre feet of that water arrived between Feb. 5 and Feb. 20. That’s nearly as much water stored behind Grand Coulee Dam, which is Washington’s largest constructed reservoir.

Why is this so important? Our snowpack is a significant water supply. In fact, it’s the largest reservoir of water in our state. For the Cascade Mountains, snowpack is responsible for about 78 percent of the runoff.

Farmers depend on this water supply to support their crops; fish need ample river water to survive; and many communities’ drinking water comes from snowpack runoff.

As a general rule of thumb, it takes about 10 inches of snow to make an inch of water. That conversion is dependent on temperature and other factors. Western Washington usually gets more water per inch of snow than Eastern Washington.

During our recent snow adventure, the National Weather Service in Seattle recorded snow-to-water ratios ranging from 17:1 (think Utah-like ski powder) to 3:1 (almost too dangerous for snowballs).

At the Stampede Pass SNOTEL location, southeast of Snoqualmie Pass, snow depth increased 35 inches –  while snow water equivalent increased 4.6 inches. In other words, for every 10 inches of snow, we gained about 1.3 inches of water.  

For every yin there is a yang

The good news, as already illustrated in this blog, is we have much needed snow in the mountains. An added bonus is the recent cold snap has acted like a freezer for the snow, keeping it high in the mountains.

With that said, it’s only February and there is a lot of snow season ahead of us. It may seem hard to believe, but even with our recent cold spell, temperatures across most of the state have been higher than normal since Oct. 1, the beginning of the water year.  

The National Oceanic and Atmospheric Administration’s Climate Prediction Center (CPC) is predicting that March temperatures have an equal chance of being above normal, below normal or normal. But for the three-month period of March – May, the CPC forecasts higher odds for above normal temperatures.  

If that forecast holds true, we may be lucky to maintain our current position, relative to average conditions.

You can learn more about water supply conditions by visiting our website.

By Jeff Marti, Water Resources Drought Coordinator

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