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Posted at 12:10 PM ET, 07/08/2011

Record snowpack across Rockies continues its midsummer melt

Areas in bright green indicate where flood warnings or advisories are currently in effect in the West. (National Weather Service)
After record snowfall buried parts of the Rockies last winter and well into spring, many western states are feeling the effects of a rapidly melting snowpack. As an area of high pressure developed over the West last week, soaring temperatures accelerated snowmelt and continued to send torrents of water down local rivers and streams.

In the wake of historic flooding along parts of the Missouri River, flood warnings or advisories have also been issued in several western states, including Wyoming, Idaho, Montana, and Nevada. In Montana, rising waters in the Yellowstone River have hampered clean-up efforts after an oil pipeline burst there a week ago.

Yosemite’s Bridal Veil Falls after a season of normal snowfall (By author)
California has also seen rising river levels in the Sierra Nevada. At Yosemite National Park, melting snows have captivated park visitors with even more magnificent waterfalls than usual, but unfortunately also led to two deaths last week.

Beneficial effects

While the rapid snowmelt has proved hazardous to some areas, the lingering snowpack has been welcome news to cities across the Southwest. According to the Associated Press, melting snows in Wyoming, Utah and Colorado are flowing into the Colorado River Basin and replenishing crucial water supplies in Arizona, Nevada, and Southern California.

Lake Mead, which supplies much of the region’s water supply, saw its water levels fall to a historic low in late 2010 following a decade-long drought. However, a moderate La Niña lasting through May of this year contributed to above average precipitation/snowfall across the northern and central Rockies, and water levels in Lake Mead are expected to increase by about 40 feet in the coming months.
Precipitation relative to average across the contiguous U.S. December through May with rankings. (NOAA)
A map of precipitation patterns (right) across the continental U.S. spanning both meteorological winter and spring (Dec 2010-May 2011) illustrates how nearly every western state experienced above normal precipitation over a 116-year period, with Montana and Wyoming both featuring their wettest combined meteorological winter and spring.

How much snow is left?

Even after weeks of substantial melting, last winter’s historic snowfall across the Rockies means the summer sun still has some work to do. Weekly reports published by the USDA’s Natural Resources Conservation Service indicate that many high elevations still have significant amounts of snow this late in the season. Just two weeks ago, snowpack measurements on the Olympic Peninsula in Washington were 39,100 percent of normal (or nearly 400 times the average for this time of year).

Fourth of July skiers, some wearing shorts, at Lake Tahoe. (Associated Press)
Not surprisingly, the stable snowpack has been a boon to ski resorts across California, Utah, and Colorado, which drew excited crowds of skiers over the holiday weekend. Some resorts just ended their record longest ski season, after getting close to 800 inches of snow (or about 67 feet!).

For D.C. and most of the country, however, snow was simply not on the Fourth of July agenda.

By  |  12:10 PM ET, 07/08/2011

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