Avalanche Advisory: Wednesday - Dec 25, 2019

THIS AVALANCHE ADVISORY EXPIRED ON December 26, 2019 @ 6:51 am
Avalanche Advisory published on December 25, 2019 @ 6:51 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center

Merry Christmas and Happy 4th day of Hanukkah!  With over a foot of new low density snow in the last 3 days and continuing moderate SW winds, Avalanche danger will remain at MODERATE at tree line and above today due to sensitive wind slabs.  LOW avalanche danger exists in lower elevations and in sheltered terrain.    

 

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

8-15”+ of very low density new snow fell mostly on the 22nd and 23rd with surprisingly light winds.  Winds increased substantially yesterday out of the SW, exceeding the forecast and gusting into the 50s over higher ridge tops thru last night.  Snow banners could be seen over many ridges, and Mammoth ski patrol reported easy triggering of fresh wind slabs throughout the day (12-18” deep).  SW winds are forecasted to continue today with gusts to 30ph at upper elevations.  Be on the lookout for denser wind deposits just below ridge lines, side walls of gullies and other catchment zones on NW thru NE thru SE facing terrain.  Use clues such as blowing snow, cornice formation and shooting cracks to help identify and avoid these areas.  Winds appear to be considerably decreased as of 7am today, and if they don't increase don't forget that slabs formed yesterday can still be sensitive.  If one of these wind slabs is triggered in an area with an underlying weak faceted snow layer, the resulting avalanche could be much larger than expected.    

 
advisory discussion

Recent field observations have found many areas of weak faceted snow under either melt-freeze crusts or thicker old stout wind-board.  Up to now these weak layers have not led to unstable slopes, for either there hasn’t been a cohesive enough slab above (melt-freeze crust scenario), or the overlying wind-board is very strong and supports itself.  However if these weak layers exist under areas of recent new wind-loading, they may now be a real threat.  

 

Melt-Freeze crust / facet combo:  With the new wind-loading, areas may now exist where a cohesive slab does lie on top of the fragile melt freeze crust/facet combination.  A failure could propagate much further than expected across a slope.  

 

Wind-board / facet combo:  A smaller wind slab avalanche could be enough force now to trigger a deeper failure under the stout wind-board, also resulting in a much larger than expected avalanche.

 

Do your own localized assessments in safe areas, and recognize the potential that may exist.  Our range is huge, so please share your findings with us thru our observation page. 

 

This light snow has made for great riding conditions, but remember it's still a very thin snowpack in many areas! Beware of those lurking rocks and logs!  Also watch out for your own slough as this light snow flows down the slope with you epecially in confined steep terrain.

recent observations
Submit Snowpack Observations
Submit Avalanche Observations

-12/24 - Lundy Canyon - Winds and weak layers.

-12/24 - Mammoth - Sherwins - New snow and winds.

-12/24 - Convict - Mini Morrison - New snow, melt-freeze/facet combo, ridgetop winds.

Weather and CURRENT CONDITIONS
weather summary

Unstable cold weather continues thru Thursday with light amounts of new snow accumulation, highs near 20°F near 10,000’, and continued light to moderate winds especially at upper elevations.  Winds will continue out of the SW today, gusting to 30mph over ridge tops, but become Grinch tonight as they shoo Christmas and shift out of the NE tonight thru Thursday and increase in intensity, 

 
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Wednesday Wednesday Night Thursday
Weather: Mostly cloudy. Chance of snow. Snow levels below 7000 feet. Chance of precipitation is 40%. Mostly cloudy. Chance of snow. Snow levels below 7000 feet. Chance of precipitation is 35%. Mostly cloudy. Chance of snow through the day. Snow levels below 7000 feet. Chance of precipitation is 30%.
Temperatures: 20 to 26. deg. F. 11 to 16. deg. F. 20 to 26. deg. F.
Mid Slope Winds: Light winds. East around 15 mph. Gusts up to 25 mph increasing to 35 mph after midnight. Northeast around 15 mph. Gusts up to 30 mph increasing to 40 mph in the afternoon.
Expected snowfall: Up to 1 inch. | SWE = less than 0.10 inch. in. Up to 1 inch. | SWE = less than 0.10 inch. in. No accumulation. | SWE = less than 0.10 inch. in.
Over 10,000 ft.
Wednesday Wednesday Night Thursday
Weather: Mostly cloudy. Chance of snow. Snow levels below 7000 feet. Chance of precipitation is 50%. Mostly cloudy. Chance of snow. Snow levels below 7000 feet. Chance of precipitation is 40%. Mostly cloudy. Chance of snow through the day. Snow levels below 7000 feet. Chance of precipitation is 35%.
Temperatures: 14 to 20. deg. F. 6 to 11. deg. F. 13 to 19. deg. F.
Ridge Top Winds: Southwest 15 to 20 mph with gusts to 30 mph. East 15 to 25 mph. Gusts up to 25 mph increasing to 35 mph after midnight. East 15 to 30 mph with gusts to 45 mph.
Expected snowfall: Up to 1 inch. | SWE = less than 0.10 inch. in. Up to 1 inch. | SWE = less than 0.10 inch. in. Up to 1 inch. | SWE = less than 0.10 inch. 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 ...