Mammoth Basin Snowpack Summary - 2015-02-05 07:08

Avalanche Advisory published on February 5, 2015 @ 7:08 am
Issued by Sue Burak - Inyo National Forest
Snowpack Discussion

Finally winter will return after a long, frustrating wait. There were a few weak storms in January that brought cloudy skies but little precipitation. Temperatures fluctuated from mild to warm to cold and the snow surface and the snowpack changed grain shapes along with temperature fluctuations. Faceted grains were unexpectedly strong and did not react in snowpack instability tests.

The series of storms will hopefully add a significant load to the existing pack but I anticipate the avalanche problems will be a result of the strong to extreme winds that will create wind slabs and storm slabs within the new snow. There is always a possibility avalanching could occur on old snow and snow stability will be monitored on Saturday. Avalanche problems will be posted but no danger ratings assigned.

Despite being in a time warp in January, now is the time to think about avalanches. Change batteries in your beacons, practice some search patterns, dust off the probes and check shovel blades and handles. Here are a couple of videos to get started.


recent observations

The recent warm period took a toll on mid elevation snowpacks in the Lakes Basin and June Mountain areas. Snow depths decreased from 20" to 16 and 18" in the upper Mammoth Basin and mid elevations on June Mountain lost at least 2" of snow. A thick melt freeze crust exists on northerly aspects from 8,500 to about 10,000 ft in the Mammoth Lakes Basin. Underneath the crust, the layer of snow that fell last week is moist and consists of rounded grains. Mid pack snow grains are rounded facets and the snow is moist.

Snow cover is sparse on flat terrain and many areas of bare ground exist that were snow covered this last weekend. 

CURRENT CONDITIONS Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: 34 deg. F.
Max. temperature in the last 24 hours: 48 deg. F.
Average wind direction during the last 24 hours: WSW
Average wind speed during the last 24 hours: 50 mph
Maximum wind gust in the last 24 hours: 56 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 16 inches

A wind advisory is in effect today, followed by a High Wind Warning on Friday. Southwest winds gusting to 70 mph are expected in areas like the Mammoth Lakes Basin and June Mountain. Higher elevations will see stronger winds gusting to 100 mph.

By Friday, snow is expected to start falling but accumulations won't start until Friday night. By Saturday afternoon, up to 14-15" of new snow could accumulate in the Lakes Basin and the mid elevations on June Mountain. The Mammoth Crest and San Joaquin Ridge, including the Negatives could receive up to 20". Snowfall will be accompanied by strong winds.

This is the first significant storm in 7 weeks. Snow levels will be high, at the Twin Lakes elevation and mid station on June Mountain.  The best case scenario is 18 to 20" of snow above 9,400 ft and 7 to 8" of snow in the town of Mammoth. The worst case scenario is 6 to 8" of snow above 9,400 ft and rain in the town of Mammoth.

The wind is a 100% certainty in both scenarios.


Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
  Thursday Thursday Night Friday
Weather: clear, windy partly cloudy chance of snow
Temperatures: 50 deg. F. 34 deg. F. 46 deg. F.
Wind direction: SW SW SW
Wind speed: 30-50 30-40 50-60
Expected snowfall: 0 in. 0 in. T in.
Over 10,000 ft.
  Thursday Thursday Night Friday
Weather: clear, windy partly cloudy, windy Chance snow
Temperatures: 40 deg. F. 28 deg. F. 35 deg. F.
Wind direction: SW SW SW
Wind speed: 45-55 55-65 60-80
Expected snowfall: 0 in. 0 in. t in.

This snowpack summary applies only to backcountry areas outside established ski area boundaries. This snowpack summary only describes general avalanche conditions and local variations always occur. This snowpack summary expires 24 hours after the posted time unless otherwise noted. The information in this snowpack summary is provided by the USDA Forest Service who is solely responsible for its content.

-- placeholder --

ESAC receives significant financial support from ...