Mammoth Basin Snowpack Summary - 2015-04-25 09:21

THIS ADVISORY EXPIRED ON April 27, 2015 @ 9:21 am
Avalanche Advisory published on April 25, 2015 @ 9:21 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.

Today, all wind loaded slopes are suspect and should be approached with caution.  Watch for obvious signs of loading such as cornices, rounded drifts and rippled texture of the snow surface.  Avoiding slopes where these signs are present will be a simple way to stay out of trouble. 

Snowpack Discussion

The winter that wouldn’t start now won’t end.

There are two avalanche concerns today. The first question is how well this new snow is bonding to the old surface. 7 inches of snow has fallen on Mammoth Pass and at the ski patrol study plot it’s likely there will be at least 12” of new snow by this evening.  Westerly winds are strong enough to create areas of wind drifted snow and wind slabs on all wind loaded slopes and on any slope steeper than 35 degrees.

Temperatures are in the low to mid 20’s and are expected to remain cold through the storm. This will help the new snow stick in place. There are a few warning signs to look out for today and tomorrow; cracks shooting out from your skis and recent avalanches are both signs of instability. Dig a quick extended column test in the new snow to see if the column propagates a fracture; if it does, descend another slope.

The next snowpack summary will be issued Sunday morning.

recent observations

Cloudy skies and mild spring temperatures the last few days added a lot of energy to the snowpack and several large wet loose snow avalanches were seen in the Hammil Bowl area. These old snow surfaces are getting buried under dry winter snow today. Winds at Horseshoe Lake are gusting to  35 mph from the southwest so areas of wind drifted snow and wind slab formation is likely today on exposed high elevation leeward slopes.

CURRENT CONDITIONS Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: 23 deg. F.
Max. temperature in the last 24 hours: 32 deg. F.
Average wind direction during the last 24 hours: WSW
Average wind speed during the last 24 hours: 40 mph
Maximum wind gust in the last 24 hours: 50 mph
New snowfall in the last 24 hours: 7 inches
Total snow depth: 7 inches

A late season storm is bringing snow to the eastern Sierra today. Over 5 inches of snow has fallen and snowfall rates of up to 2 inches an hour are expected to continue until the afternoon.   Accumulations of up to 12” are possible in the higher terrain of the Mammoth Lakes Basin and Tioga Pass.

This morning, temperatures are in the mid 20’s and westerly winds are blowing steadily at 30 mph at the top of Mammoth Mountain. After the storm passes, winds will shift to the north. Sunday will be clear and cold with moderate north winds blowing 20 to 35 mph along ridgetops.

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 partly cloudy sunny
Temperatures: 30 deg. F. 25 deg. F. 44 deg. F.
Wind direction: West north north
Wind speed: 20-30 30-45 15-25
Expected snowfall: 12 in. 0 in. 0 in.
Over 10,000 ft.
  Saturday Saturday Night Sunday
Weather: snow cloudy sunny
Temperatures: 26 deg. F. 19 deg. F. 36 deg. F.
Wind direction: west north north
Wind speed: 25-35 15-25 gusts to 50 mph 20-25
Expected snowfall: 12 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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