Eastern Sierra Avalanche Forecast - 4/26/14

Avalanche Advisory published on April 26, 2014 @ 9:20 am
Issued by Sue Burak - Inyo National Forest

New snow and very strong winds have created dangerous wind slabs on exposed slopes on north to east facing terrain today in the Mammoth area.  These areas  have a CONSIDERABLE danger rating. Strong southwest to west winds yesterday afternoon and overnight transported the new snow into unstable drifts and slabs that will remain sensitive to skier triggering today. Caution is advised on all steep wind loaded slopes above treeline- natural avalanches are possible and skier triggered slides are likely.

Clues indicating wind loaded slopes include fat, pillowed features and thick, dense, or firm snow. Watch for and avoid these drifted areas in open, exposed terrain on north to east aspects. Terrain protected from the wind will have a MODERATE danger today.

3. Considerable


Above Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

2. Moderate


Near Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

No Rating


Below Treeline
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
  • Type ?
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Yesterday and last night, two feet of new snow accumulated and strong southwest and west winds transport it into drifts on leeward slopes.  The most likely place to trigger the 1 to 2” deep wind drifts will be on upper elevation slopes facing north, east and southeast, with drifts more scattered at the mid elevations. Natural avalanches are possible and human triggered slides are likely on steep slopes with fresh wind drifts.

Avoid steep slopes with recent wind drifts, and convex shaped terrain where the slope angle climbs into the mid and upper 30's. If you see signs of instability such as clean shears or cracking, you'll want to limit your skiing and riding to lower angle terrain.

Today, make it a point to look for signs of instability- hollow sounding wind slabs, deep unsupported wind drifts and convex slopes in alpine and in steep glades.

advisory discussion

A powerful late season storm added another 2 to 3 inches of water to the snow pack. This storm is the third largest storm of the season and the second largest in terms of water content.

Due to strong solar heating and long days, the window of instability is much shorter than during the winter. Storm snow has already settled an inch this morning. However, in high elevation alpine terrain where the wind continues to transport snow,  snow accumulated at 2-3 inches an hour for around 15 hours and added 3 inches of water during that time. The snow is still adjusting to the rapid change and continued wind transport will act to maintain unstable conditions today. 


recent observations

Morning  temperatures are in the teens. Storm totals this morning range from 30 inches on the Mammoth Pass snow pillow, 24 inches at the Sesame Street study plot, 10" at Rock Creek and around 10" at Ellery Lk. Winds on Mammoth Mountain were 20-30 mph from the southwest during peak snowfall at Main Lodge. WSW winds blew for the past 24 hours at 50-60 mph at the top of Mammoth Mountain.  Winds at Ellery Lake blew from the south during the storm but this morning, winds are from the northwest.

weather summary

Clear skies this morning will give way to high clouds and partly cloudy skies as another storm passes to the north. Temperatures remain 10 to 15 degrees below normal today and tomorrow and winds will be breezy from the west at 20 to 30 mph.

Drier and warmer weather is expected next week but unsettled conditions may return by the end of the week.

Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: 13 deg. F.
Max. temperature in the last 24 hours: 26 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 30 mph
Maximum wind gust in the last 24 hours: 40 mph
New snowfall in the last 24 hours: 24 inches
Total snow depth: 40 inches
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: mostly sunny, then clouds clear sunny
Temperatures: 31 deg. F. 20 deg. F. 37 deg. F.
Mid Slope Winds: W W W
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
Saturday Saturday Night Sunday
Weather: slight chance of snow clear sunny
Temperatures: 28 deg. F. 16 deg. F. 35 deg. F.
Ridge Top Winds: W W W
Expected snowfall: 0 in. 0 in. 0 in.
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