Eastern Sierra Avalanche Forecast - 4/28/14

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THIS AVALANCHE ADVISORY EXPIRED ON April 29, 2014 @ 7:02 am
Avalanche Advisory published on April 28, 2014 @ 7:02 am
Issued by Sue Burak - Inyo National Forest
bottom line

The avalanche danger is MODERATE. The likelihood of wet loose avalanches increases today as snow at or near the surface becomes wet. The danger will rise through the day as warming temperatures and direct sun soften surface crusts, melt the bonds between snow grains, and create soft, cohesion-less snow at and near the snow surface.

How to read the advisory

Bottom Line

The avalanche danger is MODERATE. The likelihood of wet loose avalanches increases today as snow at or near the surface becomes wet. The danger will rise through the day as warming temperatures and direct sun soften surface crusts, melt the bonds between snow grains, and create soft, cohesion-less snow at and near the snow surface.

Avalanche Problem 1: Loose Wet
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Today's clear skies and increasingly warm temperatures will elevate the danger of wet snow avalanches.The snow will weaken on sunny slopes first, but the danger will be higher where there is more fresh snow to entrain in loose snow slides. Few places will be exempt from this hazard today; triggering wet, loose-snow avalanches will be possible even on northerly, sheltered treed slopes. Avoid being above terrain traps and pay attention to even small changes in elevation and aspect, which can make big differences in stability. Mid-slope pockets of wet snow may be more easily-triggered than snow closer to ridge lines.

 

Avalanche Problem 2: Wind Slab
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    Decreasing Danger

Several days of strong winds have created wind slabs on the lee sides of ridges and terrain features like rocky ribs. It's possible some slopes were cross loaded. Swirling winds can form wind slabs anywhere on a slope exposed to the wind. Look out for recent avalanches and rounded pillows of wind drifted snow- recent deposits of wind drifted snow may be sensitive to the weight of a skier or rider. 

advisory discussion

Today will be a return to spring and along with a return to spring, a return of the wet snow avalanche problem. Winds calm down, skies are clear this morning and the full strength of late April sun is cooking the snow surface. 

Damp or wet loose or slab avalanches will be more likely on steep slopes facing the sun. This type of instability can develop quickly today. So watch for the development of damp or wet surface snow layers on these aspects. Remember that surface snow sun balls and rollers often precedes loose snow avalanche activity. You can test for loose snow instability by pushing snow onto test slopes from a safe location. It is a good plan to avoid slopes below cliffs and gullies.

Wind slab avalanches are the main concern on steep high elevation north facing slopes. At the same time, wet avalanches will become the main concern this week. The snowpack will become warmer and wetter each day. Nights will warm up also and the overnight freeze will be shallow as the week progresses.  Regardless of the avalanche problem, always look carefully for recent avalanches, wet or dry, as these are the number one sign of unstable snow.

recent observations

The snow sensors at Mammoth Pass and the patrol study plot on Mammoth Mountain show 10 to 12 inches of snow settlement.The snow depth sensors at Ellery Lk and Tioga Pass are not working so it's hard to tell how much snow fell but it's possible one to 2 feet fell during the storm. A winter storm dropping 2 feet of dry snow doesn't stay dry for very long at the end of April.

Winds were blowing yesterday from the south on June Mtn, the WSW on Mammoth and mostly from the north and northwest at Ellery Lake. Riders in the Mt. Humphrey's area reported lots of snow blowing around, forming wind slabs on east and northeast aspects. 

Recent avalanche activity included dry and wet loose slides on east facing aspects.

CURRENT CONDITIONS Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: 24 deg. F.
Max. temperature in the last 24 hours: 34 deg. F.
Average wind direction during the last 24 hours: WSW
Average wind speed during the last 24 hours: 45 mph
Maximum wind gust in the last 24 hours: 69 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 31 inches
weather

A few degrees of warming yesterday but highs were still winter-like, reaching the low 30's at the 9,000 to 10,000 ft elevations.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
  Monday Monday Night Tuesday
Weather: sunny clear sunny
Temperatures: 50 deg. F. 33 deg. F. 55 deg. F.
Wind direction: W NW NE
Wind speed: 10-15 10-15 15
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
  Monday Monday Night Tuesday
Weather:
Temperatures: 48 deg. F. 25 deg. F. 52 deg. F.
Wind direction: W NW NE
Wind speed: 10-15 10-15 15
Expected snowfall: 0 in. 0 in. 0 in.
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