Avalanche Advisory: Thursday - Dec 19, 2019

THIS AVALANCHE ADVISORY EXPIRED ON December 20, 2019 @ 6:59 am
Avalanche Advisory published on December 19, 2019 @ 6:59 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center

Isolated pockets of MODERATE avalanche danger exist on northerly facing slopes at tree line and above where it may be possible for a human to trigger a dense stubborn wind slab sitting on weakening loose snow grains. This is of particular concern for areas outside of Mammoth that have shallower snowpacks.  

 

 

 

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.

1. Low

?

Below Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
    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

Although there has been no recent avalanche activity reported, snow pit tests yesterday in VA Lakes produced some alarming results.  Areas were found where thick hard wind slab failed easily on top of soft weakening / faceting snow, and these results propagated across large columns.  Where this set-up exists, if a person hit just the right weak spot, a resulting hard slab avalanche could result in injury or worse especially in consequence terrain.  Sidewalls of gullies and below ridgelines are areas of particular concern.  Our field observations are still limited making it important for you to continue to perform your own localized tests.  Dig down into that firm wind board or dense pillow to check out what is underneath.  Realize that the edges of slabs where they are thinner is where it is more likely to trigger a failure.  Winds yesterday were seen transporting snow even below tree line in open exposed areas.  It is possible that new softer wind deposits exist that are still sensitive to human triggering as well.   

 
advisory discussion

It was a tricky call this morning deciding between a Low and Moderate danger rating.  Ultimately the limited amount of field observations, the great expanse of our forecast zone, and the tremendous amount of variability that exists is keeping confidence low.  While yesterday’s concerning ECT test results were only from one area, it is hard not to imagine that other areas with shallow snow packs could harbor a similar set-up.  It is important to do your own localized assessments, and please share your findings with us thru our observation page!      

 
recent observations
Submit Snowpack Observations
Submit Avalanche Observations

-12/18 - VA Lakes: Wind slabs failing in pit tests - propagating ECT tests, faceting grains.

-12/18 - Mammoth - Mammoth Crest: Ridgetop and lake level winds, deteriorating melt freeze crust, faceting grains.

-12/18 - Mammoth - Punta Bardini: Weaknesses below Melt-freeze crust, propagating ECT results. 

Weather and CURRENT CONDITIONS
weather summary

High pressure builds today and tomorrow before winds increase on Saturday ahead of a cold front bringing chances of snow and cold temperatures for Sunday and Monday.

 

For today expect sunny skies, highs near freezing around 10,000’ and moderate west winds with gusts into the 30s.    

 
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: Sunny then becoming partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 10%. Partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 0%. Partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 0%.
Temperatures: 33 to 39. deg. F. 20 to 25. deg. F. 36 to 42. deg. F.
Mid Slope Winds: West around 15 mph with gusts to 30 mph. Southwest around 15 mph with gusts to 30 mph. South around 15 mph.
Expected snowfall: No accumulation. | SWE = none. in. No accumulation. | SWE = none. in. No accumulation. | SWE = none. in.
Over 10,000 ft.
Thursday Thursday Night Friday
Weather: Sunny. Snow levels below 7000 feet increasing to 7000 feet in the afternoon. Chance of precipitation is 10%. Partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 0%. Partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 0%.
Temperatures: 26 to 32. deg. F. 19 to 24. deg. F. 29 to 35. deg. F.
Ridge Top Winds: West 15 to 20 mph with gusts to 35 mph. Southwest 15 to 20 mph with gusts to 35 mph. Southwest 15 to 25 mph. Gusts up to 35 mph in the afternoon.
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.

ESAC receives significant financial support from ...