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Purple Rain

How will the current snowpack situation affect Washington this summer?

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Editor’s note: Purple Rain is a column that explores relevant weather topics in the Seattle region, highlighting research conducted by UW faculty.

It is around this time of year that the word “snowpack” begins to circulate among Washingtonians. While the first thing that comes to mind regarding snowpack might be winter recreational activities including skiing and snowboarding, it also determines many other things, including water resources and wildfires.

With winter weather winding down in Washington and the forecast looking warm and dry for the foreseeable future, snowfall in the mountains has essentially ended for the season.

Last Friday, Washington state climatologist Nick Bond met with local organizations and government agencies to discuss the current state of the snowpack.

“Traditionally, we consider the first of April, end of winter,” Bond said. “Essentially the snowpack at this point is what we have to get us through the drier weather we have in the summer months.”

Snowpack is a measure of the snowfall in the mountain regions. It is used interchangeably with snow-to-water equivalent (SWE), which calculates the amount of liquid water if all of the snow were to melt. When looking at SWE, the most valuable information is measuring current SWE to the 1981-2010 median.

Snowpack in Washington is important for a few reasons, the first being water supply. Unlike California, the reservoirs in Washington do not have multi-year water capacity. In the Pacific Northwest, much of the region’s water reserves are stored in the upper altitudes as snowfall, which slowly melts and replenishes the reservoirs throughout the summer.

“Seattle’s reservoirs, we have two of them, they hold a pretty good amount of water,” atmospheric sciences professor Cliff Mass said. “Enough maybe to get through one season, maybe, but the snowpack is an important addition to it. We can get by with what is in the reservoirs, but it’s just on the edge.”

Those in western Washington shouldn’t have to worry about a water shortage this summer, though, as much of the region received average to slightly above-average precipitation. SWE in regions west of the Cascades and in the Olympics are all slightly above average, from 108-121% of normal.

While the current situation bodes well for the summer, things looked grim earlier in the winter.

Winter weather started warm and dry in November. In early December, the snowpack was well below-average throughout the whole state, with the central Puget Sound hitting rock bottom at only 8% of normal Dec. 5.

A stormy January featured low snow levels, even impacting Seattle, which helped the snowpack recover to near normal, setting the table for healthy snowfall through the rest of the winter.

While the snowpack remains healthy to the west, concerns lie on the other side of the mountains, especially in the Upper Yakima region, where the snowpack is currently at 85%.

“The only kind of potential real problem areas are on the east slopes of the Cascades,” Bond said. “The snow is in pretty good shape, but it’s kind of dry there in terms of how much precipitation has occurred in the lower elevations of the mountains. Soil moistures are lower than usual and they are in a slight drought.”

Although water resources should be enough for irrigation, that doesn’t mean that there won’t be any impacts this summer.

As seen in recent years, wildfire season in the Pacific Northwest can be dangerous, even deadly. With a lot of vegetation to feed it, fires can rage through the Cascades, threatening infrastructure as well as causing human health concerns due to smoke.

“It turns out if the snow goes away sooner, the landscape can dry out that much sooner,” Bond said. “We’ve seen that in some of the past springs, especially in 2017 and 2018 and years before, some big fire seasons. There are a lot more wildfires on the east side of the Cascades than the west. That north-south strip east of the crest, that’s a concern. It means the fire season could just be starting that much earlier.”

As for the rest of spring and into summer, the biggest help to prevent wildfires would be for the weather to remain cool and wet. In the meantime, all that’s left to do is speculate about the fire season ahead.

Reach reporter Anthony Edwards at Twitter: @edwardsanthonyb

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