Avalanche Advisory: Saturday - Jan 30, 2021

THIS AVALANCHE ADVISORY EXPIRED ON January 31, 2021 @ 6:46 am
Avalanche Advisory published on January 30, 2021 @ 6:46 am
Issued by Steve Mace - ESAC

CONSIDERABLE avalanche danger exists near and above treeline today while MODERATE danger exists below treeline. Human triggered wind slab avalanches are likely today on W-N-E-SE slopes near and above treeline. Persistent slab and storm slab avalanches are also possible today. Dangerous avalanche conditions exist. 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: Wind Slab
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Moderate to Strong SW winds continued to transport snow Near and Above treeline throughout the day yesterday.  Expect resulting wind slabs to be large today and sensitive to human trigger.  While winds are forecasted to drop significantly today the low-density nature of our recent snow may allow for some transport even at lower wind speeds. Be suspect of terrain features that encourage drifting such as the leeward sides of ridgelines, gully features, and cross-loaded depressions. Human triggered avalanches are likely today and Naturally occurring avalanches remain possible. Be particularly aware if you notice the winds outperforming the forecast. 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.  

Avalanche Problem 2: Persistent Slab
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Our recent storm provided the forecast area with a much-needed blanket of snow it has also brought about a new set of challenges. First, a significant load has been added to a minimal and, in many areas weak base. While this load may have been enough to tip the scales on its own in some areas, in others the snowpack may still be hanging in the balance. The weight of a skier might be all that is needed to trigger a large destructive avalanche.  Persistent problems require persistent patience and extensive evaluation. The distribution of potential persistent slab avalanches became much harder to identify after our recent new 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 to. 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 3: Storm Slab
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Significant settlement has occurred in the short time since the storm ended. There is still a chance for a skier to trigger a large storm slab avalanche today however point release avalanches may be more problematic.  These loose sluffs of snow have the potential to be quite large particularly in areas that received more snow out of our recent storm. Be cautious in terrain over 30° today and be cognizant of your exposure to terrain features that increase the consequences of avalanches. This includes road cuts, gully features cliff bands, mid-slope depressions, and exposed areas under rooflines in town. 

advisory discussion

As the skies clear and we move into a period of quiet weather, don’t let your powder fever lure you into making poor decisions. More avalanche related fatalities occur during periods of CONSIDERABLE hazard than any other. Human-triggered avalanches are likely today and resulting avalanches have the potential to be large and destructive. Our forecast area provides a unique challenge to the backcountry enthusiast. The sheer size and diversity of our terrain often mean a dramatically different snowpack from one end to the other. This latest storm is a great example of this. While an eye-popping 8 ft of snow was recorded in the Mammoth area over a 72hr period, snow totals from areas south of Mammoth were significantly less. There are also places near the crest that likely received even more snow. This wide range of snow totals has a large impact on local hazards and travel implications. Take our persistent slab problem for instance. Counterintuitively, areas south of Mammoth with shallower snowpacks, (3-4 ft new snow) may provide a more problematic snowpack for the backcountry traveler. These areas held very little snow before this past week and the distribution of the persistent problem (old snow) will be more isolated. However, it will also be easier for a skier to impact these lower weak layers, potentially triggering a sizable avalanche. Conversely, in areas that received the high end of the snow totals (6-8+ft), these lower weak layers are more specific in distribution. The deeper overlying snow means it will be much harder for a skier to impact these lower layers, but a resulting avalanche would be much larger and more destructive.

In addition to the risk of avalanches today, there remains a risk of deep snow immersion. An otherwise benign fall could lead to suffocation in our deep unconsolidated snowpack.

Weather and CURRENT CONDITIONS
weather summary

Expect partly cloudy skies today with mild temperatures and light to moderate winds out of the west. No precipitation is expected today.

Quiet weather is slated to stick around through the weekend before another significant winter storm early next week.

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: Sunny, then becoming partly cloudy. Partly cloudy Partly cloudy
Temperatures: 28-34 deg. F. 14-19 deg. F. 31-37 deg. F.
Mid Slope Winds: Light winds light winds becoming south around 15 mph with gusts to 30mph after midnight South 10 to 20 MPH. Gusts to 30 mph increasing to 55 mph in the afternoon
Expected snowfall: o in. 0 in. 0 in.
Over 10,000 ft.
Saturday Saturday Night Sunday
Weather: Partly cloudy mostly cloudy becoming partly cloudy Partly cloudy
Temperatures: 23-29 deg. F. 11-16 deg. F. 25-31 deg. F.
Ridge Top Winds: West around 15 mph in the morning becoming light southwest around 15 mph. Gusts up to 30 mph after midnight Southwest 15 to 20 mph with gusts to 30 mph increasing to 20to 35 mph with gusts to 55 mph in the afternoon
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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