Avalanche Advisory: Friday - Dec 7, 2018

Avalanche Advisory published on December 7, 2018 @ 6:24 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center

Natural and human triggered avalanches large enough to be of concern are unlikely. However as E-SE-S-SW slopes warm from sunny skies and milder temperatures today, small loose wet activity is likely.   

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Above Treeline

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Near Treeline

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Below Treeline
Avalanche Problem 1: Loose Wet
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Very Likely
  • Size ?
    Very Large

Widespread sunny skies are expected today with milder temperatures.  This will be the first time that some slopes see the sun since Monday before up to 8” of new light snow has fallen on them. Expect to see small loose wet activity on slopes facing E-SE-S-SW as the sun warms them throughout the day. Small rollerballs are likely to originate near cliff bands where the heated rocks will warm the surrounding snow to a greater extent.  This activity should remain fairly small today, and it is unlikely (but not impossible) that they would result in a slide large enough to affect a person. This warming could also result in some rocks becoming dislodged in steep terrain.  It is good practice to make note of when this loose wet activity is occurring on specific slope aspects, and avoid these aspects during that time.  

advisory discussion

While overall stability of the snowpack seems very good, there have been several interesting things happening to the surface of the snowpack over the last couple of days that could affect future stability.  The unusually calm winds and right amount of air humidity has led to some widespread surface hoar formation in some areas such as VA lakes (perhaps many more areas, let us know if you see it!). If winds don’t pick up and destroy it before more snow comes next week, it could act as a fragile buried weak layer.  Prior to yesterday many mid to upper elevation areas sat in a cold layer of moist clouds, which ended up depositing a very thin layer of ice (call it a zipper crust) to the snow surface.  This may have gotten faceted away, but it is also possible that it could encourage a thin layer of facet growth that could also become a concern if it gets buried by new snow in the future.    

The more immediate concern today, all-be-it a small concern, is small loose wet activity.  Yesterday, low clouds and warmer temperatures began to warm up the snow on upper elevation sunny aspects which were above the clouds as well as on all aspects at lower elevations that remained in the humid cloud layer. Small rollerballs were seen originating near cliff bands.  Today, with more widespread sun expected at all elevations, light winds, and milder temperatures, expect to see small loose wet activity more consistently throughout the forecast zone at all elevations on sunny aspects from E-SE-S-SW.  

A brief season history:  Our snowpack began 2 weeks ago at Thanksgiving.  Prior to this there was virtually no snow covering any of the mountains.  Thanksgiving week storms brought in 2-3.5’ of snow accompanied by strong SW winds, providing a supportable, all-be-it shallow base of snow and start to the backcountry touring season with few if any underlying weak layer concerns.  Time allowed the windslabs to stabilize, and then a slow moving weak low pressure system brought light snowfall and surprisingly light winds on Tuesday and Wednesday, dropping up to 8” of very light low density snow, leading to a slight possible avalanche concern of very small isolated wind slabs on the leeward side of uppermost ridges.  

Early season obstacles exist!  Plenty of rocks, logs, and tree stumps are lurking just under the surface, which has led to injury and broken equipment already.  Take your time, be careful, and don’t end your season before it barely begins! 

weather summary

Up to 8” of very light snow fell between Tuesday morning and Thursday morning, with very light winds. Low level clouds remained widespread yesterday.  Today, expect sunny skies as high pressure moves back in, continued light winds and milder temperatures reaching the low 30s above 10,000’.  

Chances of very light precipitation returns Monday thru next week as several weak low pressure systems may brush by our region. 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Friday Friday Night Saturday
Weather: Mostly sunny above 8000 feet. Clear Sunny
Temperatures: 32 to 37 deg. F. 13 to 19 deg. F. 34 to 39 deg. F.
Mid Slope Winds:
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
Friday Friday Night Saturday
Weather: Mostly sunny above 8000 feet Clear Sunny
Temperatures: 28 to 33 deg. F. 11 to 16 deg. F. 28 to 33 deg. F.
Ridge Top Winds: Southwest West
Expected snowfall: 0 in. 0 in. 0 in.
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 Snowpack Summary is provided by the Eastern Sierra Avalanche Center, who is solely responsible for its content.

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