Avalanche Advisory: Sunday - Jan 31, 2021

THIS AVALANCHE ADVISORY EXPIRED ON February 1, 2021 @ 6:24 am
Avalanche Advisory published on January 31, 2021 @ 6:24 am
Issued by Steve Mace - ESAC

Dangerous avalanche conditions exist today. Large and destructive persistent slab avalanches are our main concern and will be most likely on Northerly and Easterly terrain at all elevations. Natural and human triggered wind slab avalanches will also be possible today near and above treeline.  It is important to consider that even a small wind slab might be enough to trigger a much larger persistent slab avalanche. CONSIDERABLE avalanche danger exists near and above treeline while MODERATE danger persists below treeline. Careful snowpack evaluation, cautious route-finding, and conservative decision making are essential.

 

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: Persistent Slab
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Our recent storm snow has begun to consolidate into a supportable and cohesive slab of new snow.  The thickness of this Slab will vary from one end of the range to the other, but the common thread is that a significant load has been added to a minimal and, in many areas a VERY weak base. While this load may have been enough to tip the scales on its own in some areas (See Ob HERE), in others the snowpack may still be hanging in the balance. The weight of a skier or a small wind slab avalanche might be all that is needed to tip the scales and trigger a large destructive avalanche. This is evidenced by a Large Skier triggered avalanche that occurred yesterday in the Sherwins. (See Observation HERE)

Persistent Slab problems challenge our patience. Managing this problem requires extensive evaluation and deliberate terrain choice. The distribution of our persistent slab problem became much harder to identify after our recent snow. Northerly and Easterly facing terrain that still held snow from November and December are our potential problem areas.  Don’t be afraid to investigate the lower reaches of the snowpack to see if old snow is present in the areas you wish to travel. This may mean digging all the way to the ground to evaluate the lower snowpack. Remember that persistent slab avalanches often propagate across and beyond terrain features that would otherwise confine surface instabilities such as wind or storm slab and in some cases persistent slab avalanches can be remotely triggered from adjacent slopes. Give yourself a wide safety margin, be wary of hazards that may reside above you, and use terrain choice to limit your exposure.

Avalanche Problem 2: Wind Slab
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Despite the relatively light winds yesterday some significant wind transport was observed in the late afternoon near and above treeline. Winds are expected to increase back into transportable speeds today. Expect these moderate to strong winds to redistribute loose surface snow near and above tree line. Wind slabs will vary in size and sensitivity today from small and sensitive to large and stubborn.  It is imperative to remember that even a small wind slab avalanche today might be enough to trigger a much larger and more destructive Persistent slab avalanche.  Be suspect of terrain features that encourage drifting such as the leeward sides of ridgelines, gully features, and cross-loaded depressions. Blowing snow, recent cornice growth, stiff hollow feeling upside-down snow, and a textured, uneven snow surface are all signs of recent wind transport. Use these signs to identify and avoid slopes with recent wind deposits. 

 

advisory discussion

Make no mistake we are dealing with a dangerous snowpack at the moment. One that we are not used to seeing here in the Sierra. Human triggered avalanches are LIKELY today and resulting avalanches have the potential to be very large and destructive.  Top of our minds is our Persistent slab problem.  This problem is entering a frightening phase where avalanches are becoming more difficult to trigger, predict and manage while continuing to show the size potential to destroy a large truck or small house and certainly large enough to bury or kill a person. Patience is KEY right now, allowing powder fever to get the best of you could be a costly mistake today. Skill alone is not enough to manage this hazard. Extensive evaluation and deliberate terrain choice are crucial. When uncertainty is high, keep it simple and avoid avalanche terrain.

Weather and CURRENT CONDITIONS
weather summary

Expect another pleasant day today with mild temperatures, moderate winds out of the southwest, and partly cloudy skies.

This period of quiet weather is slated to stick around through the weekend before another significant winter storm moves into our forecast area late tomorrow or early Tuesday.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Sunday Sunday Night Monday
Weather: Partly cloudy then becoming mostly cloudy. Mostly cloudy. Mostly cloudy then becoming partly cloudy. S
Temperatures: 31 to 37. deg. F. 21 to 26. deg. F. 32 to 38. deg. F.
Mid Slope Winds: South 15 to 20 mph with gusts to 35 mph. South 15 to 20 mph with gusts to 35 mph. South 15 to 30 mph with gusts to 55 mph.
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
Sunday Sunday Night Monday
Weather: Partly cloudy then becoming mostly cloudy. Mostly cloudy. Partly cloudy.
Temperatures: 26 to 32. deg. F. 18 to 23. deg. F. 25 to 31. deg. F.
Ridge Top Winds: Southwest 20 to 30 mph with gusts to 50 mph. Southwest 20 to 35 mph. Gusts up to 45 mph increasing to 55 mph after midnight. Southwest 25 to 35 mph increasing to 30 to 45 mph in the afternoon. Gusts up to 70 mph.
Expected snowfall: 0 in. 0 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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