Avalanche Advisory: Monday - Jan 4, 2021

THIS AVALANCHE ADVISORY EXPIRED ON January 5, 2021 @ 6:50 am
Avalanche Advisory published on January 4, 2021 @ 6:50 am
Issued by Chris Engelhardt - Eastern Sierra Avalanche Center

Rapid loading of heavy wet snow combined with extreme SW winds will ramp up the avalanche danger to CONSIDERABLE today. Fresh WIND SLAB & STORM SLAB above and near tree line on N-E ASPECTS will be of most concern. Conservative decision making and identification of terrain features conducive to capturing wind transported snow will be essential. This projected fast addition of heavy moisture laden snow upon an existing weak, thin and fragile snowpack will set up conditions for likely human triggered avalanches and possible natural avalanche activity.  

3. Considerable

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

3. Considerable

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

2. Moderate

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Below Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
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Fresh wind slabs will be possible to trigger on Northerly-Easterly Aspects today, primarily in the Upper elevations and Near Tree Line. SW Winds combined with intense snowfall rates will produce sensitive and reactive wind deposits that may be easily triggered by a skier. Additionally triggering a wind slab today may cause older persistent slabs residing on weak, loose, degraded snow to step down causing larger more destructive avalanches. Small human triggered wind slab avalanches will be possible in many areas and may be larger and more destructive in larger terrain features that are capturing fresh wind loaded snow. These specific areas will be slopes adjacent to ridgeline, deposition zones under cliff bands, and steeper convex terrain such as rollovers and cross loaded gully features.  Stay focused on your exposure to down slope hazards, terrain traps, and cliffs where even a small slide could prove to be hazardous. Be on the lookout for fresh pillows of snow and fat looking drifts to identify fresh wind slab.

Avalanche Problem 2: Storm Slab
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It is a major RED FLAG to get a rapid load of heavy moisture laden snow upon a weak, shallow snowpack. If snow and SWE (Snow Water Equivalent) totals reach the high end of projections, as in upwards of 16” of new snow with over 1” of water, this new load will cause unstable and dangerous avalanche conditions. Continued study of the snowpack throughout December has shown definite and proven propagation potential in old weak snow at the base of our thin snowpack. With little time to adjust, today’s potential rapid onset of weight in storm snow could cause significant avalanche activity. The colder, shady N-E aspects are of most concern, especially near tree line where the snowpack has the most significant amount of loose faceted snow at the base. This “upside down” structure could cause STORM SLABS to step down deeper to the old weak snow and cause larger more destructive avalanches. A human trigger may be just the shock to upset a tenuous balance.

advisory discussion

While wetter, warmer conditions will help the new snow bond to old snow surfaces, the potential for a significant amount of added weight today could conversely also cause hazardous avalanche conditions. Patience is advised to see how much snow we ultimately receive and how snowpack conditions adjust to the new load. Low angle terrain, avoidance of terrain traps, and awareness of exposure from overhead will be key today and in the days ahead when clear conditions develop.

Weather and CURRENT CONDITIONS
weather summary

A fast moving storm will blow over the area today with rapid snowfall, and strong to extreme SW winds. The spread on snow accumulation could be from 2” on the low end to potentially upwards of 16” especially on the crest. Snow is projected to increase in intensity late morning through the afternoon with heavy accumulation rates at times. SW winds will ramp up through the day with the most extreme gusts in the afternoon at ridge top where 100+mph velocities are projected. Temperatures were warm last night, generally above freezing around 9000ft ahead of this moisture laden storm and will continue to be just around freezing for the upper elevations and upwards of 39degF below 10000ft. It’s going to be a wet one out there today, so be prepared. Conditions are expected to calm down with lighter snow continuing into the evening hours with moderating winds.

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: Mostly cloudy. Chance of snow in the afternoon. Partly cloudy then becoming clear. Chance of snow Sunny.
Temperatures: 31 to 39 deg. F. 16 to 22 deg. F. 34 to 40 deg. F.
Mid Slope Winds: Southwest 15 to 25 mph with gusts to 50 mph increasing to 25 to 35 mph with gusts to 65 mph in the afternoon. Southwest 30 to 40 mph with gusts to 65 mph becoming west 15 to 25 mph with gusts to 50 mph after midnight West around 15 mph with gusts to 30 mph in the morning becoming light.
Expected snowfall: 80% probability of 1 to 5 inches. 20% probability of 5 to 8 inches. in. 90% probability of 1 to 3 inches. 10% probability of 3 to 5 inches. in. 0 in.
Over 10,000 ft.
Monday Monday Night Tuesday
Weather: Mostly cloudy. Snow likely in the afternoon. Mostly cloudy then becoming clear. Snow likely in the evening. Sunny.
Temperatures: 24 to 30 deg. F. 12 to 17 deg. F. 28 to 34 deg. F.
Ridge Top Winds: Southwest 30 to 45 mph with gusts to 75 mph increasing to 50 to 65 mph with gusts to 105 mph in the afternoon. Southwest 50 to 70 mph with gusts to 105 mph becoming west and decreasing to 30 to 50 mph with gusts to 80 mph after midnight West 15 to 25 mph. Gusts up to 35 mph decreasing to 25 mph in the afternoon.
Expected snowfall: 70% probability of 1 to 5 inches. 30% probability of 5 to 10 inches. in. 80% probability of 1 to 3 inches. 20% probability of 3 to 6 inches. in. 0 in.
Disclaimer
This Avalanche Advisory is designed to generally describe avalanche conditions where local variations always occur. This product only applies to backcountry areas located outside established ski area boundaries. The information in this Avalanche Advisory is provided by the Eastern Sierra Avalanche Center, who is solely responsible for its content.

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