Avalanche Advisory: Sunday - Jan 20, 2019

THIS AVALANCHE ADVISORY EXPIRED ON January 21, 2019 @ 6:46 am
Avalanche Advisory published on January 20, 2019 @ 6:46 am
Issued by Steve Mace - ESAC

The avalanche danger is CONSIDERABLE today at mid and upper elevations and MODERATE at lower elevations.  Sensitive wind slab and persistent slab avalanches will be our primary concern today, however, with up to 20" of new snow predicted over the next 24 hours expect storm slab development throughout the day and into the evening.​

3. Considerable

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

3. Considerable

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

2. Moderate

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Below Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
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Ample new snow and moderate to strong southwest winds are expected today at upper elevations. Expect to find fresh, sensitive wind slabs developing in exposed areas at mid and upper elevations.  Use surface clues to identify and avoid wind-loaded slopes over 35°.  Fresh cornice growth, blowing snow, and uneven snow surfaces, are all signs that wind loading is occurring nearby.  While fresh wind slabs will be of most significant concern today last weeks extreme wind event distributed snow in unpredictable ways. It will not be impossible to find lingering wind slabs in more sheltered areas even at lower elevations.​

Avalanche Problem 2: Persistent Slab
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Last weeks storm snow has settled into a thick cohesive slab with the recent stint of warm weather.   This slab is sitting on top of loose faceted snow that continues to be observed near the ground throughout the forecast area.  Many natural avalanches occurred on these buried facets during the last storm cycle.  Including a very large avalanche in a forested area of the Sherwins, and multiple explosive triggered avalanches at Mammoth Mountain.  It is important to remember that even relatively small avalanches will have the potential to step down to these deeper layers creating a much larger avalanche.  As this slab continues to build these avalanches will become harder to trigger.  However, resulting avalanches are likely to be very large and destructive, propagating long distances and traveling far into runout zones.  
Also concerning is the presence of buried surface hoar which was reported in many sheltered areas before this past storm event.  Avalanches releasing on this dangerous weak layer have the potential to propagate long distances and run in lower angle terrain. Forecaster confidence on the distribution of preserved buried surface hoar is low; careful snowpack evaluation will be essential and conservative route choice is highly recommended. ​

Avalanche Problem 3: Storm Slab
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While primarily a concern for the late afternoon and evening hours, expect to see storm slabs developing as the storm intensifies and snow totals add up. Shooting cracks, wumphing, and recent avalanche activity are all signs of instability.  Care should be taken in sheltered areas where the slope angle is greater than 35°.​

advisory discussion

As recent observations have shown persistent slabs have the potential propagate in surprising and unpredictable ways. They are often triggered remotely and can propagate beyond terrain features that otherwise confine storm or wind slabs, making them particularly challenging to manage.  Poor structure and weak faceted grains have been observed throughout the forecast region, and recent avalanches have shown the destructive nature of these slides. Persistent slab problems can challenge our patience and decision-making ability making good communication and conservative route choice essential. 

 

Weather and CURRENT CONDITIONS
weather summary

Expect to see cloudy skies, a chance of snow today with a slight chance of thunderstorms this afternoon.  Temperatures are expected to be around freezing at upper elevations today, dropping sharply to single digits tonight.  Winds will be moderate to strong out of the southwest gusting to 80 mph on ridge tops. Up to 20" of snow is expected at upper elevations over the next 24 hours, the bulk of which will arrive this evening.

Tomorrow will be mostly cloudy with a chance of 1-3 " of snow.  Temperatures are expected to be in the low to mid teens with moderate winds continuing out of the southwest. 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Sunday Sunday Night Monday
Weather: Chance of snow with a slight chance of thunderstorms this afternoon Snow through the night Mostly cloudy then becoming partly cloudy. Chance of snow.
Temperatures: 34-42 deg. F. 14-19 deg. F. 22-28 deg. F.
Mid Slope Winds: Southwest 15-34mph increasing to 30-40 mph in the afternoon. gusts up to 80mph South 30-45 mph with gusts to 80 mph becoming southwest 20-30 mph with gusts to 60 mph West 15-25 mph with gusts to 45 mph.
Expected snowfall: 2-3" in. 6-16" in. 1-2" in.
Over 10,000 ft.
Sunday Sunday Night Monday
Weather: Chance of snow with a slight chance of thunderstorms this afternoon Snow through the night. Mostly cloudy then becoming partly cloudy. Chance of snow.
Temperatures: 26-32 deg. F. 8-13 deg. F. 13-19 deg. F.
Ridge Top Winds: Southwest 35-55mph with gusts to 80 mph. southwest 40-60 mph with gusts to 85 mph. West 25-40 mph with gusts to 60 mph.
Expected snowfall: 2-4" in. 8-18" in. 1-3" 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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