Avalanche Advisory: Tuesday - Dec 29, 2020

THIS AVALANCHE ADVISORY EXPIRED ON December 30, 2020 @ 7:00 am
Avalanche Advisory published on December 29, 2020 @ 7:00 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center

Even though snowfall has stopped, avalanche danger will actually be greater today due to strong North winds creating sensitive WIND SLABS on W-S-E facing terrain at mid and upper elevations. New slabs of snow will also make larger PERSISTENT SLAB avalanches more possible, especially on East and West facing slopes.  Human triggered avalanches will be possible, and a natural avalanche is not out of the realm of possibility where winds continue to load snow.  MODERATE avalanche danger exists near treeline and above, and LOW does not mean NO below treeline.  Small loose sloughs will also be possible in steep sheltered terrain. And continue to be aware of many slightly buried obstacles! 

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.

1. Low

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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
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4-8” of new snow, with over a foot at higher elevations above June, has fallen between Sunday afternoon and yesterday with unusually calm winds.  North winds are now cranking over ridgetops with gusts expected up to 70mph.  Sensitive wind slabs will continue to build throughout today on W-S-E facing terrain at treeline and above.  Watch for dense pockets of freshly wind deposited snow below ridgelines, sidewalls of gullies and on the leeward-side of mid-slope terrain features. Use clues such as cornice formation, blowing snow and uneven surfaces to help determine which steep slopes to avoid. Human triggered avalanches will be possible, and natural avalanches are not out of the realm of possibility with continued wind-loading thru today.  Sunshine in the afternoon heating up S to W west facing slopes will increase this concern. 

Avalanche Problem 2: Persistent Slab
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A fresh dense wind-transported snow slab deposited ontop of areas with a weak underlying snowpack structure is a scary thought. Triggering a larger-than-expected PERSITENT SLAB avalanche is more possible today than previous days.  Due to the wind direction out of the North, this concern is greatest on East and West facing terrain with fresh wind-deposited snow.      Whoomphing and shooting cracks continue to be reported, and propagating test results have been widespread.  It is hard to know which slopes have enough anchors to keep it from sliding, so avoid East and West facing slopes greater than 30° where a new dense slab of snow exists with weak sugary facets buried at the base. This doesn’t mean that North facing slopes are totally in the clear, for even as light new snow settles, it could become more slab-like as well. And remember, this kind of avalanche could easily release well above you and spread out much further than expected.       

Avalanche Problem 3: Loose Dry
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Many small loose dry avalanches were reported yesterday.  While unlikely to be large enough to bury someone, it could take someone off their feet into dangerous obstacles. Don’t count on being able to safely outrun a slough today given the shallow snowpack and plethora of obstacles. Concern will be greater where greater amounts of new snow has fallen, such as higher elevations above June.  

advisory discussion

Our persistent slab problem continues to be a challenge.  We have the weakest early season snowpack than we have seen in a long time, and for the most part the weak basal facets don’t seem to be strengthening.  What has been lacking is the right combination of a significant enough slab and lack of underlying anchors such as logs, rocks and bushes and steep enough terrain that is accessible. Will todays wind-deposited snow be enough to tip the balance in some places?  

     

Weather and CURRENT CONDITIONS
weather summary

High pressure will setup today thru tomorrow keeping conditions dry before another fast-moving storm brings chances of minor light snowfall Wednesday night into Thursday morning. Expect cloudy skies this morning to give-way to sunshine this afternoon, and slightly warmer temperatures reaching the low to mid 20s around 10,000’.  Winds will be significantly increased out of the North with gusts up to 50mph at mid-elevations and up to 70mph over ridgetops. 

The first week of the new year continues to look promising for back-to-back storms with moisture amounts measured in inches instead of tenths-of-an-inch.  

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Tuesday Tuesday Night Wednesday
Weather: Mostly cloudy then becoming sunny. Snow levels below 7000 feet. Chance of precipitation is 0%. Clear. Snow levels below 7000 feet. Chance of precipitation is 0%. Partly cloudy then becoming mostly cloudy. Snow levels below 7000 feet. Chance of precipitation is 0%.
Temperatures: 24 to 30. deg. F. 10 to 15. deg. F. 32 to 38. deg. F.
Mid Slope Winds: North 15 to 30 mph with gusts to 50 mph. Northwest 15 to 25 mph with gusts to 45 mph in the evening becoming light. Light winds.
Expected snowfall: No accumulation. | SWE = none. in. No accumulation. | SWE = none. in. No accumulation. | SWE = none. in.
Over 10,000 ft.
Tuesday Tuesday Night Wednesday
Weather: Mostly cloudy then becoming sunny. Snow levels below 7000 feet. Chance of precipitation is 0%. Clear. Snow levels below 7000 feet. Chance of precipitation is 0%. Partly cloudy then becoming mostly cloudy. Snow levels below 7000 feet. Chance of precipitation is 0%.
Temperatures: 16 to 22. deg. F. 6 to 11. deg. F. 24 to 30. deg. F.
Ridge Top Winds: North 30 to 45 mph with gusts to 70 mph. North 25 to 35 mph with gusts to 65 mph becoming northwest 15 to 20 mph with gusts to 40 mph after midnight. Northwest 15 to 20 mph with gusts to 30 mph.
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.

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