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Environment

Hot, Dry Conditions Take a Heavy Toll on Western U.S. Snowpack

ImaGeo iconImaGeoBy Tom YulsmanFebruary 5, 2018 12:19 AM
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An animation of satellite images shows just how much thinner the snowpack in California's Sierra Nevada range is this year compared to the same time last year. (Images: NASA Worldview. Animation: Tom Yulsman) Thanks especially to warm temperatures, plus a lack of precipitation, the snowpack in most of the Western United States is in bad shape right now — nowhere worse than in California's Sierra Nevada range. For all but the northern reaches of the region, snowpack stands at no more than about 50 percent of average, and in many places it's much worse. For California, snowpack as of today, Feb. 4, is at just 25 percent of normal. Luckily, the state's reservoirs are still brimming with water, thanks to last year's copious rain and snowfall. This will provide a sizable cushion for the year ahead should warm temperatures and scant precipitation continue. “There’s still a lot of the winter left,” says Frank Gehrke of California's Department of Water Resources, quoted by the Sacramento Bee. “Anything can happen as we move through the rest of the season.”

Still, the comparison with last year couldn't be more stark — as the animation of satellite images above dramatizes. Both images were collected by NASA's Terra satellite as it passed over the Sierra Nevada range. An image taken on Jan. 29, 2017 shows an extensive blanket of snow, whereas one acquired on Feb. 3rd of this year shows shockingly less.

Colorado, where I live, also is in pretty bad shape, with snowpack at just 35 percent of average for Feb. 4. I mention this because snowmelt and runoff from our mountains supplies the lion's share of the water for the Colorado River Basin. Nearly 40 million Americans rely on the Colorado River system for drinking water and to support farming, recreation and other livelihoods.

Here's what snowpack looks like throughout the West:

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Those blue and green circles in the northern tier of the region — from Washington into Idaho and Montana, and down into Wyoming — are indicative of healthy snowpack. This part of the West may be benefiting from La Niña, a climatic phenomenon characterized by cooling in parts of the tropical Pacific, with impacts on weather patterns far afield. La Niña tends to tip the odds in favor of wetter than average conditions in the northern reaches of the western United States. But many other factors influence weather patterns as well. So I don't think it would be accurate to say anything stronger than this: What we've seen so far in that northern tier region is consistent with La Niña. (For more on how La Niña may be influencing our weather, see this excellent post at NOAA's ENSO Blog.) Meanwhile, all those red, orange and yellow circles paint a grim picture when it comes to snow. Warm temperatures have been a bigger issue than lack of precipitation. California, for example, has received 70 percent of its average precipitation since the water year began on Oct. 1, yet snowpack is at just 25 percent. Similarly, while Colorado's snowpack is at 35 percent of average, it has actually received 62 percent of its average precipitation. Warm temperatures have been causing snowpack to melt, and for more precipitation than normal to fall as rain rather than snow. California still has three months to catch up, and much of the rest of the West has even more than that. So let's keep our fingers cross that the pattern changes soon.

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