PRINCETON, N.J. — Across the U.S., a greater percentage of winter precipitation is falling as rain, with potentially severe consequences in Western states where industries and cities depend on snowpack for water, and across the country wherever there is a winter sports economy.
A new Climate Central analysis, Meltdown, based on 65 years of winter precipitation data from more than 2,000 weather stations in 42 states, found a decrease in the percent of precipitation falling as snow in winter months for every region of the country.
“As the planet warms, the shift to a greater percentage of winter precipitation falling as rain has already begun,” said Jen Brady, Sr. Analyst at Climate Central and author of the report.
In western states where snowpack is critical, we found decreases in the percent of winter precipitation falling as snow at all elevations between sea level and 5,000 feet.
Above 5,000 feet there is clear regional variation.
In Colorado, Wyoming, Utah, California, Nevada, and New Mexico there was either no trend toward rain or a slight trend toward more snow at elevations 5,000 feet and higher.
In stark contrast, between 5,000 to 8,000 feet in Montana, Idaho, and Arizona, between 75 and 78 percent of all stations report an increase in rain as a percentage of total winter precipitation. Oregon has only one station above 5,000 feet, but it too reported a strong increase in rain vs. snow as winter precipitation. Washington has no stations at this elevation.
These very different results at the same elevations may indicate that the interior West and central Rocky Mountain states are subject to a different climate pattern that has delayed the shift toward more rain as a percent of winter precipitation at elevations of 5,000 and above.
The Northwest – A Region at Risk
The Pacific Northwest has been the hardest hit, with low elevation snow on a clear path toward oblivion: 81 and 91 percent of stations under 2,000 feet in Washington and Oregon, respectively, show a trend toward a lower percentage of precipitation falling as snow over the 65 years analyzed.
At 2,000 to 5,000 feet in Washington and Oregon the effect is similar, with 63 and 71 percent of stations recording lower percentage of precipitation falling as snow during the winter snow season, over the period analyzed. In the interior Northwest, Montana and Idaho showed the same basic trend between 2,000 to 5,000 feet, with 64 and 82 percent of stations reporting a shift to more rain as a percentage of winter precipitation.
At higher elevations in Montana and Idaho, the shift was even stronger, with 75 and 78 percent of stations reporting a decrease in the percentage of precipitation falling as snow at 5,000 to 8,000 feet. The single station at this elevation in Oregon reported the same trend.
“Serious water reliability issues may be just around the corner in the Pacific Northwest,” said Brady.
East of The Rockies
East of the Rockies, as elevations decline, the results are even stronger, with 20 out of 30 states showing a strong trend toward a greater percentage of winter precipitation falling as rain, than snow. For every one of these states, save Texas, winter is the fastest warming season.