Mammoth Basin Snowpack Summary - 2015-04-10 07:10

THIS ADVISORY EXPIRED ON April 14, 2015 @ 7:10 am
Avalanche Advisory published on April 10, 2015 @ 7:10 am
Issued by Sue Burak - Inyo National Forest
Avalanche Character 1: Wind Slab
Wind Slab avalanches release naturally during wind events and can be triggered for up to a week after a wind event. They form in lee and cross-loaded terrain features. Avoid them by sticking to wind sheltered or wind scoured areas.

It's possible skiers and riders could trigger wind slab avalanches today in isolated areas below ridgelines and in alpine cirques that collect snow from cliffs and steep terrain above. Answer the question that should be on your mind, "How well is the new snow bonding to the old snow surface" by testing small slopes and performing quick stability tests.


Avalanche Character 2: Loose Wet
Loose Wet avalanches occur when water is running through the snowpack, and release at or below the trigger point. Avoid very steep slopes and terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.

If skies clear for extended periods today and through the weekend, direct sunshine will make both natural and human triggered loose snow avalanches (sluffs) possible in steep terrain. The new cold snow will be very sensitive to heating, and wet loose sluffs may become easy to trigger on steep slopes. The peak of wet snow instability will occur over the weekend before a cooling trend and cold winter weather returns next Monday.

Snowpack Discussion

Plenty of skin wax is mandatory to enjoy the approaches to spring powder in the Mammoth Basin. Pent up demand for powder skiing exceeded supply on Mammoth Mountain on Wednesday, while backcountry slopes were unpopulated but with some instability within the new snow.

By yesterday, powder conditions were dialed back by strong April sun. Based on limited observations, variable snow conditions exist in the backcounty with crusts reported on east facing slopes in the June Mountain area. A report from Virginia Lakes noted wind loading in the form of small cornice formations but no wind slab was found on the slope the party skied.  Storm snow in the Red Cone area was sensitive in an ECT test (ECTP) at 8 to 10” down from the surface on Wednesday but storm snow settled and the new snow was bonding well to the old, icy snow surface yesterday.

The question today is still, “How well is the new snow bonding to the old snow surface”? Answer this question by testing small slopes and performing quick stability tests. Overall stability is pretty good, but heightened avalanche conditions on certain terrain features mean human triggered avalanches remain possible in isolated areas on steep north facing aspects. The photo shows the terrain where it may be possible to trigger an avalanche today.

recent observations

Control work on Mammoth Mountain Wednesday produced widespread avalanching that ran long distances. In the backcountry, a few loose snow avalanches were observed. ECT results in storm snow on Wednesday were not seen in a limited number of stability tests yesterday, indicating stability is improving.  


CURRENT CONDITIONS Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: 20 deg. F.
Max. temperature in the last 24 hours: 29 deg. F.
Average wind direction during the last 24 hours: SSW
Average wind speed during the last 24 hours: 10-15 mph
Maximum wind gust in the last 24 hours: 35 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 18 inches

After morning lows in the teens, temperatures will reach the upper 30’s and low 40’s above 9,500 ft.  Night time lows will be in the upper teens to mid 20’s through the weekend. Mostly sunny conditions are expected through tomorrow before a weak storm passes to the north bring a chance of snow to the mountains on Sunday. Sunday will be warm with a chance of thunderstorms.

Unsettled and wintry weather returns Tuesday with strong winds and chances for snow.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
  Friday Friday Night Saturday
Weather: mostly sunny partly cloudy mostly sunny
Temperatures: 44-50 deg. F. 20-25 deg. F. 46-52 deg. F.
Wind direction: Light light light
Wind speed:
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
  Friday Friday Night Saturday
Weather: partly cloudy partly cloudy mostly sunny
Temperatures: 35-43 deg. F. 17-23 deg. F. 38-45 deg. F.
Wind direction: SW SW SW
Wind speed: 0-10 0-10 0-10
Expected snowfall: 0 in. 0 in. 0 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.

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