Tuesday, May 23, 2017

Melting Snowpack Poses Dangers in the Sierra Nevada This Week

Chris Dolce
Published: May 23,2017

The Sierra Nevada snowpack is melting quickly this week as very warm temperatures grip the region, raising the risk of several dangers.
(MORE: Crews Clear Winter's Epic Snowfall in the West)

Satellite image of the snow-covered Sierra Nevada on May 19, 2017.
Snowpack in the Sierra from this past winter was still well above average to begin May. The SNOTEL network estimated water content of the snowpack in the Sierra was still from three to six times the average for the week before Memorial Day.
With well-above-average temperatures in place early this week, melting of that snowpack will be accelerated.
Rapidly increasing flows are likely on rivers and streams in the region. Flows on some waterways could be two to three times greater than normal, the National Weather Service (NWS) says.
The Walker River in western Nevada had been forecast to top a record, which could have caused significant property damage near the towns of Mason and Yerington. As of Monday, the forecast crest for the river had been reduced based on new data, with minor to moderate flooding now expected.
Preparations for the potential flooding are being encouraged. Sandbagging efforts are underway and crews are working to build up levees in Yerington, according to posts on the Lyon County, Nevada, Facebook page.
Latest river status (blue line) and forecast rise (purple line) for the Walker River near Mason, Nevada.
The Truckee River is expected to remain at levels which could lead to flooding of basements and yards of low-lying homes from near Alpine Meadows Road to Tahoe City, according to the NWS.
The Humboldt River is expected to reach moderate flood stage, which could lead to sewer backups in low spots of Winnemucca, Nevada, and flood some rural roads.
The NWS is encouraging any visitors in the larger Sierra Nevada region to avoid camping in and around rivers or streams given the projected rises and higher flows. Peak flows from snowmelt typically occur in the evening and overnight, posing a danger to campers that set up near a waterway for the night.
Another danger to consider is that the water will be very cold. That could raise the risk of hypothermia for those that spend even a small amount of time in the water.
Another warm snap kicking in Memorial Day weekend will continue to replenish rivers with snowmelt into early June.
(MORE: Summer 2017 Temperature Outlook)
MORE: California Flood Impacts 2017

The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.

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