Avalanche Advisory: Thursday - Dec 24, 2020

THIS AVALANCHE ADVISORY EXPIRED ON December 25, 2020 @ 6:22 am
Avalanche Advisory published on December 24, 2020 @ 6:22 am
Issued by Steve Mace - ESAC

MODERATE avalanche danger exists today at all elevations. Wind slabs will be the primary concern on all aspects near and above tree line. In addition, a concerning Persistent slab problem exists on northerly and easterly aspects at all elevations.

Evaluate snow and terrain carefully if you venture into the backcountry today and be wary of the very thin obstacle ridden conditions.

 

2. Moderate

?

Above Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

2. Moderate

?

Near Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

2. Moderate

?

Below Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
    Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Wind Slab
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Wind slabs will range in size and sensitivity today from fresh and reactive to older and more stubborn. Light SW winds are expected today and may limit continued slab development this morning, however, we may see more significant transport this afternoon as wind speeds pick up. While natural activity will be very unlikely, lingering wind slabs around the compass rose may still be reactive to human trigger. Some small pockets of older wind slab may exist at lower elevations, however Exposed areas and leeward catchment zones near and above tree line deserve elevated caution. Large drifts, hollow drum like 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. 

Avalanche Problem 2: Persistent Slab
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Field observations continue to identify signs of instability in the lower snowpack. Recent avalanche activity (see observation) has been noted on these weak facets lower in the snowpack. Evaluate snow and terrain carefully if you decide to head into the backcountry today. Persistent slab issues test our patience and require continuous evaluation. Don’t be afraid to dig in and get a look at the lower layers of the snowpack. Even quick probing can give you an idea if the strong over weak structure exists. 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.

advisory discussion

We have been talking a lot about the thin coverage that exists throughout the forecast area and the hazards that come with it. While the shallowly buried rocks, bushes, and trees certainty pose a hazard for those sliding on snow, the shallow nature of the snowpack has also been beneficial in some ways. With such sporadic coverage throughout the range, areas with the right set of circumstances to produce a sizable persistent slab avalanche are limited. However, a significant new load of snow may awaken the beast below. This was made evident by some recent avalanche activity where the wind deposited enough snow to tip the scales and break loose on weak faceted snow near the ground.  As we look towards the weekend and impending snowstorms, it will be important not to become complacent. Continue to investigate the snowpack carefully and be safe out there.

Weather and CURRENT CONDITIONS
weather summary

Expect mild weather today with above freezing daytime temperatures and light to moderate winds out of the Southwest. Cloud cover should build throughout the day as a quick moving storm approaches the area.

We may just be in for a White Christmas here on the eastside as the first in a series of storms moves into the region tomorrow. Only trace amounts of snow are expected during daylight hours tomorrow with more substantial snowfall predicted later in the evening and into the weekend.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Thursday Thursday Night Friday
Weather: Mostly cloudy Mostly cloudy then becoming clear Partly cloudy, chance of snow in the afternoon
Temperatures: 34-40 deg. F. 17-22 deg. F. 33-39 deg. F.
Mid Slope Winds: Light Winds Light winds, Gusts to 25mph after midnight Southwest around 15 mph. Gusts to 25 mph increasing to 60 mph in the afternoon.
Expected snowfall: 0 in. 0 in. trace in.
Over 10,000 ft.
Thursday Thursday Night Friday
Weather: Mostly cloudy Mostly cloudy then becoming partly cloudy Partly cloudy. Chance of snow in the afternoon.
Temperatures: 28-34 deg. F. 14-19 deg. F. 25-31 deg. F.
Ridge Top Winds: Light winds Southwest around 15 mph. Gusts up to 25 mph after midnight Southwest 15-30 mph. Gusts up to 30 mph increasing top 70 mph in the afternoon
Expected snowfall: 0 in. 0 in. trace 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.

ESAC receives significant financial support from ...