Avalanche Advisory: Monday - Mar 5, 2018

 
 
 
 
 
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THIS AVALANCHE ADVISORY EXPIRED ON March 6, 2018 @ 6:59 am
Avalanche Advisory published on March 5, 2018 @ 6:59 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center

While the threat of wind slabs and storm slabs have declined, the avalanche danger will be kept at CONSIDERABLE on NW-N-NE slopes where old deeply buried weak layers exist.  Large-scale slope collapses and at least one remotely triggered avalanche occurred yesterday.  Large and dangerous avalanches are possible.  This is not a normal situation for our region.  Evaluate the snowpack carefully and be conservative in your decision making to avoid being on or under steep slopes where this dangerous snowpack structure exists. 

2. Moderate

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

3. Considerable

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Near Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

3. Considerable

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Below Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Deep Slab
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Layers of weak loose faceted snow buried deeply in the snowpack which we have been monitoring and discussing throughout most of our season have now become our greatest avalanche concern.  The substantial new snow load from the Thursday – Saturday storm is now acting as a cohesive slab which can propagate deep failures large distances.  Large-scale whoomphing and even remote triggering of avalanches with large crowns were reported and observed yesterday.  Areas of greatest concern are NW-N-NE facing slopes below tree-line that had snow coverage prior to this last storm, but suspect slopes exist above tree-line as well, especially where old thick hard wind deposits are not bridging these deep weak layers.  This problem is not obvious.  Pay special attention to cues such as whoomphing and shooting cracks, investigate thru digging (over a meter deep), and if in doubt, simply avoid steep slopes.  A resulting avalanche would likely be large and destructive. 

Avalanche Problem 2: Wind Slab
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While the significant wind slabs that formed during the past storm have had time to settle, yesterday afternoon small avalanches were still triggered in isolated areas.  Greatest concern exists on NW-N-NE-E-SE slopes due to the predominant SW winds.  There was a several hour period yesterday afternoon where the winds increased and shifted out of the NE (banners could be seen over many upper elevation ridgelines) which likely formed isolated small new wind slabs which could be sensitive to human triggering on more southerly facing slopes just below ridgelines.    

Avalanche Problem 3: Loose Wet
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Sunny skies, light winds, and rising temperatures today may cause slopes that have exposure to the sun to warm enough to show some signs of instability.  Concern over small loose wet avalanches will be greatest at mid to low elevations on SE-S-SW facing slopes, especially near rock bands that heat up.  The possibility exists that this warming could be enough to weaken bonds and make a small slab release possible.   

advisory discussion

The snowpack structure this season is much more complex than we have seen in a long time.  Deeply buried weak sugary facet layers can be found through much of our region.  You won’t find this a concern in lower elevation slopes which weren’t covered in snow prior to this recent storm.  Upper elevation exposed areas could be less likely as well either due to much deeper snow deposits, or significant bridging from thick hard wind-slabs.  The middle elevations which have been covered with enough snow all season to cover up bushes and other potential anchors are the most concerning in terms of the greatest potential for a large deep slab avalanche occurring.  Besides avalanche concern, lower elevation slopes which were previously very thin or bare before this last storm have lots of barely covered obstacle.   

Weather and CURRENT CONDITIONS
weather summary

For today expect clear skies, warming temperatures with highs in the mid 20s around 10,000’, and light winds.  A high pressure ridge is moving into our area thru Wednesday, with temperatures warming by 5-10 degrees each day, before a weak low pressure trough should bring windy conditions and the possibility of light snowfall for Thursday thru Saturday, with chances increasing for a more substantial storm Sunday – Monday.

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: Sunny Clear Partly Cloudy
Temperatures: 30 to 36 deg. F. 9 to 14 deg. F. 37 to 43 deg. F.
Mid Slope Winds: Light Light Light
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
Monday Monday Night Tuesday
Weather: Sunny Clear Partly Cloudy
Temperatures: 23 to 29 deg. F. 7 to 12 deg. F. 30 to 36 deg. F.
Ridge Top Winds: Southwest Light Light
Expected snowfall: 0 in. 0 in. 0 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 Snowpack Summary is provided by the Eastern Sierra Avalanche Center, who is solely responsible for its content.

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