Avalanche Advisory: Saturday - Jan 18, 2020

THIS AVALANCHE ADVISORY EXPIRED ON January 19, 2020 @ 6:36 am
Avalanche Advisory published on January 18, 2020 @ 6:36 am
Issued by Steve Mace - ESAC

The Avalanche danger will be CONSIDERABLE at mid and upper elevations today, and MODERATE at lower elevations. Fresh, sensitive wind slabs will be the primary concern on northerly and easterly aspects at mid and upper elevations. Storm slabs will be less concerning, however still possible to find in more sheltered areas at lower elevations. Cautious route-finding and conservative decision making will be essential if you travel into the backcountry today.  

3. Considerable

?

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

3. Considerable

?

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

2. Moderate

?

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
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

6"-15" of new snow fell on Thursday night and this fresh snow was accompanied by very strong southwest winds. Gusts up to 120 mph were recorded at the top of Mammoth mountain during the storm. While decreased wind velocities will limit fresh slab development today, sensitive wind slabs remain likely at mid and upper elevations on northerly and easterly aspects. Consequential wind slabs will be most prevalent in exposed areas and leeward catchment zones near and above treeline, however, it is important to remember that strong winds can distribute snow in unexpected ways. Don’t be surprised to find wind deposits at lower elevations and further down slopes than you may typically expect to find them.  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.  Surface clues such as blowing snow, recent cornice growth, and uneven snow surfaces can help you identify and avoid areas of recent wind deposits.

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

Field observations yesterday identified new snow totals ranging from 6-15” and found the new snow to be distinctly upside-down in nature, particularly in areas affected by the wind. Storm slabs remain a possibility in steep sheltered terrain.  Be on the lookout for signs of surface instabilities such as shooting cracks, wumphing, and recent avalanche activity and be aware that loose unconsolidated sloughs can entrain quite a bit of snow and potentially carry a skier through some unpleasant terrain.  Heightened awareness is recommended in areas with terrain features that intensify the consequences of an avalanche such as slopes above cliff bands, creek beds, or thick stands of trees.

advisory discussion

After almost two weeks of low danger and variable skiing conditions, the promise of new snow and pleasant weather will be a strong pull. However, human triggered avalanches remain likely today and it will be important to approach the backcountry with patience and caution. Field observations prior to this last storm identified variable surface conditions ranging from hard slick crusts to loose and unconsolidated snow. In addition, widespread faceting has been observed both on and near the old snow surface as well as deeper in the snowpack.  This weak interface and poor structure may increase the sensitivity and size of avalanches today. Numerous natural and artificially triggered wind slab avalanches were observed yesterday with at least one remotely triggered avalanche reported by Ski Patrol at Mammoth Mountain.  While the exact circumstances are unknown it is likely that faceted grains at the interface added to the sensitivity of this avalanche.  Quieter weather this weekend promises a healing trend, but it remains to be seen how the snowpack will adjust to the new load.  Careful route-finding and conservative decision making will be imperative if you decide to head into the backcountry today. 

Weather and CURRENT CONDITIONS
weather summary

 High pressure will continue to build across the range, leading to quieter weather this weekend. Expect moderate SW winds today with ridgetop gusts reaching 40 mph, with cloudy skies and temperatures near freezing at 10,000’. 

This trend should continue throughout the weekend. A moderate winter storm is looking promising for early next week, promising snow showers and increased winds.

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: Mostly cloudy then becoming partly cloudy. Partly cloudy. Partly cloudy then becoming mostly cloudy.
Temperatures: 36 to 44. deg. F. 21 to 26. deg. F. 39 to 47. deg. F.
Mid Slope Winds: Southwest around 15 mph in the morning becoming light. Gusts up to 30 mph. Light winds. Light winds becoming southeast around 15 mph with gusts to 30 mph in the afternoon.
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
Saturday Saturday Night Sunday
Weather: Mostly cloudy. Partly cloudy. Partly cloudy then becoming mostly cloudy.
Temperatures: 29 to 37. deg. F. 19 to 25. deg. F. 32 to 40. deg. F.
Ridge Top Winds: Southwest 15 to 25 mph. Gusts up to 40 mph decreasing to 25 mph in the afternoon. Light winds becoming southwest around 15 mph with gusts to 25 mph after midnight. Light winds becoming southeast 15 to 25 mph with gusts to 35 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.

ESAC receives significant financial support from ...