Thursday, February 11, 2016

More Rain, Less Snow for U.S. Winters

As the world warms, it’s changing the essence of winter.  It’s not that less precipitation is falling (though that is happening in some areas).  It’s that less winter precipitation is falling as snow, according to a new Climate Central analysis.

Not all winter precipitation is created equal.  Less winter precipitation falling as snow is bad news for water supplies and wildfires out West and the financial fate of ski resorts across the country.

To see how winter precipitation is changing, we looked at states that all see notable amounts of snow (sorry, Florida).  Our analysis included 2,121 weather stations and looked at days with precipitation from the months that typically see at least 1 inch of snow so we could get a full sense of not just winter, but the snowy shoulder seasons as well.  In some places, this snowy season spanned October through April, while in others it only ranged December to February.  (full methodology below)

Overall, 55 percent of the stations showed a decrease in winter precipitation falling as snow, with the biggest dropoff happening in those shoulder seasons.  Rising temperatures mean hotter falls and spring arriving earlier.  The result is that precipitation falling in those shoulder months is increasingly likely to fall as rain rather than snow.

Oregon saw the biggest drop with 86 percent of its stations reporting a decline (it's neighbor to the north, Washington, had the fourth-biggest drop).  Iowa and New Hampshire round out the top three with 82 and 80 percent of their stations reporting more increasing snowy season rain, respectively.  Some states in the top 10, like Arizona, aren't snowy all over in winter, but those weather stations in the state’s mountainous regions are almost all seeing less snow now than several decades ago.

Last winter’s “wet drought” in the Pacific Northwest is a prime example of this phenomenon.  The region was only slightly drier than average, but much of the precipitation that did fall came as rain thanks to the second-mildest November to April on record.  The impacts from that and more rain on snow in general are multifaceted and frankly, none of them are very good.

More rain is a bummer for ski resorts and the people who love them.  In the Pacific Northwest, there was an immediate impact to the region with a handful of ski resorts having a curtailed season or never opening at all.

That’s because there’s no easy fix for rain falling instead of snow.  In fact, one of the biggest issues for resorts is if rain falls on snow already on the ground.

“If you get a rain on snow event or just get less snow in general, it’s hard to attract more skiers,” Elizabeth Burakowski, a postdoctoral researcher at the National Center for Atmospheric Research, said.  “No amount of grooming can make a rainy day go away.”

Read more at More Rain, Less Snow for U.S. Winters

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