Mammoth Basin Snowpack Summary - 2015-03-11 07:00

THIS ADVISORY EXPIRED ON March 13, 2015 @ 9:00 am
Avalanche Advisory published on March 11, 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.

Not much new snow is expected but combined with moderate southwest winds today and tonight, wind slabs will have a spotty distribution- their location will depend on localized wind patterns. Wind slabs resting on faceted snow could keep wind slabs unstable for a few dys after the storm.

Snowpack Discussion

After five days of cool daytime temperatures in the mid 30’s with cool to cold nights, sun affected slopes at upper elevations are softening only an inch or two deep, and loose wet avalanches are unlikely. High elevation, north facing terrain remains winter-like with settled powder in chutes and acres of faceted “recycled powder” over a firm layer providing very good skiing and riding conditions a week since the last snowfall. Southwest winds picked up yesterday by noon and the few inches of snow that could fall will be accompanied by southwest winds. Our typical southwest winds will create a wind slab problem in alpine zones. Wind slabs will be thin but will be forming on top of widespread surface facets that have given us the best skiing of the season. Thin wind slabs with facets underneath can be an unstable snow structure so evaluate high elevation exposed slopes before committing to your line.

Mid elevations on the other hand, are wet and soft by mid day and snowcover is becoming patchy. Travel is easy in the morning over firm icy crusts, but later in the day, crusts weaken and become slush. The weak faceted snow that formed in December and January have little strength mid day when the snow gets wet.  

The deep instability we found last week when column tests collapsed on depth hoar 12 inches above the ground were not seen yesterday on the Knob.

recent observations

Observations made yesterday show a snowpack in various stages of transition to spring. There are more patches of bare ground, melt freeze crusts are supportable in the morning and soften by mid-day.

The early February rain/wet snow layer is by far the dominant feature in the snowpack. Even though we observed faceting under the 4 to 5 inch knife-hard crust, it still requires determined saw work to cut it into sections that can then be removed with a shovel.  The layer is everywhere but at high elevations, it is more deeply buried under storm snow and not near as thick.

The difference in thickness between high elevation and mid elevation early February layers is seen in the photographs. The first photograph was taken by Ned Bair near the top of Mammoth Mountain and the second picture is from the 9,400 ft elevation on the Knob.



CURRENT CONDITIONS Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: 28 deg. F.
Max. temperature in the last 24 hours: 53 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 35 mph
Maximum wind gust in the last 24 hours: 46 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 30 inches

Clouds, strong winds and possible snow showers are the weather story today. Southwest winds gusting to 50 mph over the ridgetops will continue today. Daytime highs will be in the mid 30’s above 10,000 ft. and the upper 30’s at the mid elevations from 9,000 to 10,000 ft.

Tomorrow will be sunny and cool with north winds gusting to up to 25 mph. The Ridge builds back in over the West Coast on Friday, bringing above average temperatures to the area.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
  Wednesday Wednesday Night Thursday
Weather: 70% chance of a few inches of snow chance of snow clear
Temperatures: 39 deg. F. 29 deg. F. 42 deg. F.
Wind direction: SW SW N
Wind speed: 20-30 10-15 15-25
Expected snowfall: 1-3 in. 0 in. 0 in.
Over 10,000 ft.
  Wednesday Wednesday Night Thursday
Weather: Snow likely chance of snow sunny
Temperatures: 33 deg. F. 27 deg. F. 35 deg. F.
Wind direction: SW SW N
Wind speed: 30-45 20-30 15-25
Expected snowfall: 1-3 in. .5 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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