Avalanche Advisory: Saturday - Dec 19, 2020

THIS AVALANCHE ADVISORY EXPIRED ON December 21, 2020 @ 6:36 am
Avalanche Advisory published on December 19, 2020 @ 6:36 am
Issued by Steve Mace - ESAC

Snowpack Summary:

A very shallow and complex snowpack exists throughout the range. Thursday’s snowstorm added significant weight to a weak underlying snowpack. Human triggered persistent slab avalanches remain possible on northerly and easterly aspects. Evaluate snow and terrain carefully, be on the lookout for lingering wind slabs near and above tree line and move with caution. The snowpack is VERY thin, and many obstacles exist just below the surface.

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Near Treeline

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Below Treeline
Avalanche Problem 1: Persistent Slab
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Weak faceted snow from storms in early and mid-November is present on northerly and easterly aspects throughout the majority of our forecast area. Thursday’s storm added about a foot of snow and an inch of water to this sugary and unconsolidated base. Field observations continue to identify signs of instability in the lower snowpack including slope scale collapsing, surface cracks, propagating test results and several human and explosive triggered avalanches. Evaluate snow and terrain carefully if you decide to head into the backcountry this weekend. Don’t be afraid to dig in and get a look at the lower layers of the 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 hazard that may reside above you, and use terrain choice to limit your exposure.

Avalanche Problem 2: Wind Slab
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Light to moderate winds are expected to continue out of the N-NW over the weekend. A generally thin alpine snowpack and decreasing winds will limit the possibility of fresh wind slab development as we move into the weekend. While natural activity will be very unlikely, lingering wind slabs around the compass rose may still be reactive to human trigger. Exposed areas and leeward catchment zones near and above tree line deserve elevated caution. Large drifts, stiff hollow sounding surface snow, and uneven snow surfaces are all clues that indicate nearby wind deposits. Do your own localized assessments and be suspect of terrain features that encourage drifting such as the leeward sides of ridgelines, gully features, and cross-loaded depressions. 

advisory discussion

Backcountry enthusiasts find themselves in a bit of a pickle on the eastside right now. Our snowpack is very thin, and many obstacles exist throughout the landscape in the form of barely covered rocks, exposed bushes, fallen trees, and sporadic coverage. Compounding the hazardous travel conditions is our persistent slab avalanche problem. It is important to remember that the areas with the best coverage (gully features, deposition zones, and shaded northerly and easterly terrain) are also the areas where persistent slab avalanches are most likely to occur. This catch -22 has the potential to encourage us all to fall victim to our own poor judgment as we try and seek out soft turns. The promise of fresh snow and pleasant weather will be tempting as we move into the weekend, but it is important that we all temper our expectations, move with caution and evaluate snow and terrain carefully. There is a long season ahead and now is not a time to ski or ride with abandon in the backcountry.

recent observations
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12/18- Mammoth Area, Thin coverage and poor structure in the Lakes basin

12/18- Mammoth Area, Human triggered avalanche, Red Cone approach

12/18- Mammoth Area, Poor snowpack structure on Earthquake dome

12/18- June Lake Area, Shallow snow coverage on Chicken Wing

12/17- Mammoth Area, Many signs of Instability, Minaret Vista

12/17- Mammoth Area, Propagating test results in the Lakes basin

12/17- Mammoth Area, Snow conditions, Punta Bardini

Weather and CURRENT CONDITIONS
weather summary

Day time temperatures will be on a warming trend through the weekend with light to moderate winds out of the NW and mostly clear skies. Temperatures should be pleasant with highs approaching the upper 40°s below 10000’ and mid to upper 30°s at upper elevations. Light to moderate winds will continue out of the Northwest with ridgetop gusts approaching 35 mph

Dry weather should persist though most of next week with our next chance of precipitation occurring around Christmas.

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: Partly cloudy then becoming sunny. Snow levels below 7000 feet. Chance of precipitation is 0%. Clear. Snow levels below 7000 feet. Chance of precipitation is 0%. Sunny. Snow levels below 7000 feet increasing to 7000 feet in the afternoon. Chance of precipitation is 0%.
Temperatures: 37 to 43. deg. F. 22 to 28. deg. F. 40 to 46. deg. F.
Mid Slope Winds: West around 15 mph in the morning becoming light. Gusts up to 30 mph. Light winds. Light winds.
Expected snowfall: No accumulation. | SWE = none. in. No accumulation. | SWE = none. in. No accumulation. | SWE = none. in.
Over 10,000 ft.
Saturday Saturday Night Sunday
Weather: Partly cloudy then becoming sunny. Snow levels below 7000 feet. Chance of precipitation is 0%. Clear. Snow levels below 7000 feet. Chance of precipitation is 0%. Sunny. Snow levels below 7000 feet increasing to 7000 feet in the afternoon. Chance of precipitation is 5%.
Temperatures: 30 to 36. deg. F. 18 to 24. deg. F. 32 to 38. deg. F.
Ridge Top Winds: Northwest 15 to 25 mph with gusts to 35 mph. Northwest 15 to 20 mph with gusts to 35 mph. Northwest around 15 mph with gusts to 25 mph in the morning becoming light.
Expected snowfall: No accumulation. | SWE = none. in. No accumulation. | SWE = none. in. No accumulation. | SWE = none. 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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