Avalanche Advisory: Monday - Feb 1, 2021

THIS AVALANCHE ADVISORY EXPIRED ON February 2, 2021 @ 7:00 am
Avalanche Advisory published on February 1, 2021 @ 7:00 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center

A solid scary MODERATE avalanche danger exists at all elevations due to Persistent Slab and Wind Slab problems.  Intense snow fell between Wednesday and Friday leaving many feet of new snow sitting on-top of weak sugary faceted snow in many places. It could be possible to trigger a large and deadly avalanche failing on these weak layers on W-N-E facing terrain at all elevations. Today’s winds out of the SW will be stronger than they have been in several days. Watch for fresh sensitive and older more stubborn wind slabs on NW-NE-SE facing slopes near tree line and above.     

*Join ESAC Forecaster Steve Mace for Free Virtual Avalanche Awareness Event - Wed Feb 3rd (6-7:30pm): Avalanches 101.  Click here to access Zoom Event!

2. Moderate

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

2. Moderate

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

2. Moderate

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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: Persistent Slab
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The snowpack underlying all of the recent storm snow is sketchy in many areas consisting of layers of weak sugary facets.  The many feet of new snow has settled, consolidated and strengthened on-top, but the underlying facets will take a much longer time.  It’s the trickiest avalanche problem there is, as it takes a rider hitting a thin sweet spot to trigger a likely large and deadly slide.  A skier triggered one of these 2 days ago, and was extremely fortunate to get caught-up in a tree with relatively minor injuries rather than taken for a long ride and buried deeply.  Staying off and out from under slopes over ~30° facing East to North to West, or sticking to slopes that you know were bare ground before this storm are sure ways to avoid this problem, otherwise you could be rolling the dice with your life. Dig down deep into the snow and check for yourself to help you make more informed decisions.    

Avalanche Problem 2: Wind Slab
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SW winds have been transporting snow to one degree or another at higher elevations since the snow stopped falling on Friday.  These winds are forecasted to pick up to stronger levels today than they have yet, with gusts up to 80mph over ridgetops this afternoon and up to 70mph at mid-elevations.  These winds will likely extend existing wind slabs, and form new ones potentially into slightly more sheltered areas or further downslope.  NE-NW-SW facing slopes will be most suspect.  Use clues such as cornice formation, blowing snow, and surface sculpting to help you figure out where new denser sensitive wind slabs may exist.  Human triggered avalanches are possible in loaded areas especially below ridgelines, side walls of gullies and across-slope depressions and range from sensitive to stubborn. A natural avalanche could occur in an isolated area from today’s loading as well.  It is also possible that a smaller wind slab avalanche could be enough to trigger a deeper persistent slab avalanche.       

advisory discussion

The persistent slab problem that we have is not a common one we see in the Eastern Sierra.  Snow fell in November, and then sat around for nearly 2 months becoming weaker and weaker before this new substantial snow fell last week covering it up.  Add to that a new thinner faceted weak layer that formed near the top of the old snow in some places just before this storm and the situation becomes even more complex.  This top layer of facets seems more sensitive than the thicker older layer, and looks to be the culprit of the avalanche that was triggered on Punta Bardini on Saturday that could have killed the skier who triggered it.  This is a situation where you could get lucky and ride over a dangerous slope unscathed that has a shallow sensitive trigger point, or you may hit that spot and get caught in a large avalanche. Its recommended to keep it realed in for awhile longer and give some more time for confidence to grow in this suspect snowpack.

recent observations
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-1/30 - Mammoth Area – Punta Bardini: Skier triggered and caught in large persistent slab avalanche

-1/31 – Bishop – Habeggars: Weak basal facets, collapses, propagating test results

-1/31 – Near June – Chicken Wing: Propagating test results on Weak deeply buried near-surface facets

-1/31 – Bishop – South Lake: Whoomphing bellow tree line on west aspect.

-1/31 - Bishop – Bishop Bowl: Weak basal facets, new snow consolidating

-1/31 – Bishop – Bishop Bowl: Weak basal facets, wind effects

-1/31 – Convict – Mini Morrison: Avalanches near end of storm

-1/31 – Convict – Batch Plant Bowls: Strengthening snowpack where bare-ground existed before storm

-1/31 – Bishop – Buttermilk Country: Melt-freeze crust developing on sunny aspects

1/30 - Mammoth Area – Sherwins: Snow conditions

1/30 - Mammoth Area – Punta Bardini Tele Bowls: Collapsing, and recent avalanche activity

1/30 - Lee Vining: Widespread Natural activity, likely from the evening of 1/28 or the morning of 1/29

1/30 - Lee Vining – V-Bowl: Collapsing, propagating test results

1/30 - June Area – Four Seasons: Settling storm snow

1/30-June Area to Lee Vining - Large Natural avalanches observed from Hwy 395

1/30-Convict - Large Natural avalanche in Old Man’s bowl

1/30-Bishop Area- Snow conditions in Bishop bowl

Weather and CURRENT CONDITIONS
weather summary

A slight chance of snow flurries exists this morning before skies clear for the afternoon.  Winds are again on the increase out of the SW with gusts up to 80mph over ridgetops in the afternoon, and temperatures should reach near-freezing around 10,000’.  

The next storm slated for Tuesday into Wednesday unfortunately seems to be splitting and loosing strength for the Eastern Sierra.  Less than 6” of new snow is now expected.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Monday Monday Night Tuesday
Weather: Partly cloudy then becoming sunny. Slight chance of snow in the morning. Snow levels below 7000 feet increasing to 7500 feet in the afternoon. Chance of precipitation is 10%. Clear then becoming partly cloudy. Snow levels 7000 feet. Chance of precipitation is 5%. Mostly cloudy. Slight chance of snow in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 55%.
Temperatures: 32 to 38. deg. F. 21 to 26. deg. F. 29 to 37. deg. F.
Mid Slope Winds: South 15 to 30 mph with gusts to 70 mph. Southwest 15 to 25 mph with gusts to 65 mph. Southwest 15 to 30 mph with gusts to 50 mph.
Expected snowfall: Up to 1 inch. | SWE = less than 0.10 inch. in. No accumulation. | SWE = none. in. 80% probability of 1 to 5 inches. 20% probability up to 1 inch. | SWE = up to 0.25 inch. in.
Over 10,000 ft.
Monday Monday Night Tuesday
Weather: Mostly cloudy then becoming sunny. Slight chance of snow in the morning. Snow levels 7500 feet. Chance of precipitation is 15%. Clear then becoming partly cloudy. Snow levels 7000 feet. Chance of precipitation is 5%. Mostly cloudy. Slight chance of snow in the afternoon. Snow levels below 7000 feet increasing to 7000 feet in the afternoon. Chance of precipitation is 55%.
Temperatures: 25 to 31. deg. F. 17 to 22. deg. F. 21 to 29. deg. F.
Ridge Top Winds: Southwest 25 to 35 mph with gusts to 60 mph increasing to 30 to 45 mph with gusts to 80 mph in the afternoon. Southwest 25 to 40 mph with gusts to 70 mph. Southwest 25 to 40 mph with gusts to 60 mph.
Expected snowfall: Up to 1 inch. | SWE = less than 0.10 inch. in. No accumulation. | SWE = none. in. 80% probability of 1 to 5 inches. 20% probability up to 1 inch. | SWE = up to 0.25 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.

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