Mammoth Basin Snowpack Summary - 2015-02-07 07:00

THIS ADVISORY EXPIRED ON February 10, 2015 @ 7:00 pm
Avalanche Advisory published on February 7, 2015 @ 7:00 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.

Due to high snowlines, expect to find dense windslabs on north facing aspects above 8,500 to 9,000 ft. In exposed alpine terrain, also ook for wind slabs on east aspects. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard.





Avalanche Character 2: Storm Slab
Storm Slab avalanches release naturally during snow storms and can be triggered for a few days after a storm. They often release at or below the trigger point. They exist throughout the terrain. Avoid them by waiting for the storm snow to stabilize.

Storm slabs are possible on slopes facing north to east. Storm slabs break within the storm snow or on the old snow surface.

Snowpack Discussion

This snowpack summary applies to the Mammoth and June Mtn areas. Apologies for late posting- voluntary evacuations last night due to the Swall fire and loss of friend's homes required my attention this morning.

Avalanche danger increased overnight; wind loading will continue today, creating wind slabs on all lee slopes above treeline and on steep north facing slopes in the trees. Strong SW and WSW winds created touchy wind and storm slabs in exposed terrain. Temperatures generally fell during the main period of precipitation. Expect wind slabs depths of 2 feet and greater in heavily wind loaded terrain.

Continued strong winds and snowfall will keep the avalanche danger elevated through the weekend. New snow loads are falling on a shallow snowpack with many rocks of small to boulder size, downed logs and bare ground. As of this morning, there is 29” inches of snow at Mammoth Pass which is a big increase from the 18 inches measured yesterday, but the snowpack is shallow.  

Storms will continue to impact our area throughout the weekend and snow totals could be 2 feet of greater by Monday above the 9,000 ft elevation in the Mammoth Basin, San Joaquin Ridge and the June Mountain area. If precipitation rates are high, natural avalanches triggered by the wind could be widespread.

recent observations

Observations from Thursday and Friday reveal a story of shallow snowpacks with melt freeze crusts and bonded mix of crust, rounds and rounding facets on northerly aspects. Some northerly aspects above treeline continue to have lower density faceted snow below a melt freeze crust in the upper 8 inches (20 cm) of the pack.  Snowpack tests conducted throughout the month of January and the first week of February did not react despite facets under crusts.  I think the existing snowpack is in good shape to handle loading from this series of storms.

CURRENT CONDITIONS Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: 32 deg. F.
Max. temperature in the last 24 hours: 43 deg. F.
Average wind direction during the last 24 hours: WSW
Average wind speed during the last 24 hours: 60 mph
Maximum wind gust in the last 24 hours: 70 mph
New snowfall in the last 24 hours: 9 inches
Total snow depth: 1.8 inches

The atmospheric river brought a disappointing amount of snow but a lot of water to the area last night. Fierce winds fanned a destructive wild fire that destroyed homes in Swall Meadows. Snow levels fluctuated last night from 7,000 to 9,500 ft.  New snowfall totals range from 13 inches at Gem Pass, elevation 10,700 ft., to 11 inches on Mammoth Pass. Nine inches of wet snow accumulated at the Sesame Street study plot. The water content in the snow ranges from 1 to 2 inches, making for very wet, heavy snow of 12 to 20% density.  

Ridgetop winds are increasing this morning. Yesterday, lower elevations at 7,000 ft. experienced sustained winds of 40 to 50 mph with peak gusts over 80 mph. Winds at Mammoth Mountain were from 60 to 70 mph. Ridgetop winds are expected to remain strong over Mammoth and the Sierra Crest,

The National Weather Service forecast for Mono County calls for an additional foot of heavy wet snow to fall today along the Sierra Crest. A second warm storm will reach the area tomorrow afternoon with another 1 to 2 ft.  of wet snow expected to fall above 9,500 ft.  

Daytime temperatures will reach the mid 30’s today at the 9,000 ft. elevation with 3 to 5 inches of new snow expected. Temperatures at elevations above 10,000 ft. will reach the freezing (32 F) and an additional 3 to 7 inches of snow.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
  Saturday Saturday Night Sunday
Weather: Snow snow chance of rain and snow
Temperatures: 38 deg. F. 34 deg. F. 42 deg. F.
Wind direction: SW S SW
Wind speed: 30-40 20-25 25-35
Expected snowfall: 3-5 in. 1-2 in. 1-2 in.
Over 10,000 ft.
  Saturday Saturday Night Sunday
Weather: snow snow chance of snow
Temperatures: 32 deg. F. 28 deg. F. 33 deg. F.
Wind direction: SW Sw S
Wind speed: 30-40 20-25 25-30
Expected snowfall: 3-7 in. 1-3 in. 1-2 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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