Avalanche Advisory: Wednesday - Dec 23, 2020

THIS AVALANCHE ADVISORY EXPIRED ON December 24, 2020 @ 6:20 am
Avalanche Advisory published on December 23, 2020 @ 6:20 am
Issued by Chris Engelhardt - Eastern Sierra Avalanche Center

Main concerns today are WIND SLAB on steep 30deg+ terrain on ALL ASPECTS adjacent to ridgeline, convexities and other terrain features conducive to capturing wind transported snow. A concerning PERSISENT SLAB problem remains at all elevations on Northerly-Easterly terrain as well. Consider your exposure and vulnerability to terrain traps or lurking obstacles where even a small human triggered avalanche could be consequential. MODERATE avalanche danger exists not only for these avalanche problems, but equally for thin and obstacle ridden conditions.

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: Wind Slab
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Reactive wind slabs were found yesterday in the Sherwins (see obs) on NE aspects. Although they may be more stubborn to trigger today, you should still remain vigilant and be on the lookout for Wind Slab on NW-N-NE-E-S aspects. Shooting cracks, audible whoompfing or panels of firmer wind effected snow resting on top of looser, less cohesive snow will be good indicators that wind slab is present. Natural wind slab avalanches occurred on upper northerly terrain Monday night in the VA Lakes area and there remains the possibility of human triggered slides in specific areas such as slopes adjacent to ridgeline and cliff bands, steep mid slope rollovers, and features that have convex slopes optimal for capturing snow on the leeward side. Be keenly aware of your exposure in terrain choice and your vulnerability to injury even if a small pocket releases. There is so much exposed rock and other obstacles that even a small ride in an avalanche could be really hazardous. Maintain good travel protocols and identify features of concern.

Avalanche Problem 2: Persistent Slab
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Up to this point, a shallow, weak, and concerning snowpack structure exists in a majority of our northerly-easterly facing terrain. Observations throughout the forecast zone continue to show propagating results in faceted layers near the base of our thin snowpack. There was also a natural persistent slab avalanche documented in VA lakes (see obs) yesterday on a northerly aspect near 10600ft.  All elevations currently have these persistent slab conditions, so continuous evaluation is warranted with snow pits, probing, and solid awareness of your position in relation to terrain traps, such as ravines, or gullies where a small slide could potentially bury you. Steeper slopes above 30degrees are of most concern, especially where there is the lack of supporting structures in the terrain such as thick trees. Persistent slabs may be triggered from distant locations and travel over wide spaces of terrain if slopes have connected panels of snow. Shooting cracks and whoomphing are sure signs of unstable snow.

 

advisory discussion

Overall, the depth of the snowpack throughout the forecast zone remains thin and sporadic to non-existent. Recent violent winds have also left a stripped and harsh surface where snowfields actually exist amongst the landscape of rock. The deepest snowpack, which still is far from being considered good coverage, is in the Mammoth area, with the southern part of the forecast zone possessing practically no skiing potential except for a few filled in gullies and couloirs up very high. The northern part of the zone is better than the south, but the higher country with snow is still quite difficult to access at this point. The snowpack is primarily composed of weak, faceted, basal snow now capped by firmer persistent slabs with even firmer surface wind board on top. Some sheltered northerly trees still have some soft surfaces, but any aspect that has seen some sun and felt the warm temperatures of the past week has been cooked down and crusted over. There is plenty of poor structured snow that will likely be dangerous and reactive for avalanche conditions once we get a new load of snow upon it. It will be interesting to see what happens this coming weekend with slated storms on the horizon.

recent observations
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12/22 – Mammoth Area – Sherwins – reactive wind slab

12/22 – Mammoth Area – small wind slab triggered below Sherwins Ridge top

12/22 – VA Lakes – Natural Avalanche in Red Lake bowl

12/21 – Convict Lake Area – Old Man’s Bowl – thin snowpack

12/21 - Mammoth Area -Smugglers -warming & roller balls

Weather and CURRENT CONDITIONS
weather summary

It will be a sunny and warm day, with moderate easterly winds at ridge top. Temperatures will reach the high 30sF for the upper elevations and will be even warmer (42F) below 10000Feet. Christmas Eve is scheduled to be partly cloudy with continued warm temperatures and light winds as a weak upper wave moves into the area in front of an oncoming winter storm. The good news is that we are still on track for a Christmas present in the form of much needed snow starting Friday afternoon with potential of upwards of a foot of snow for the Sierra Crest. Additionally, another storm is on the horizon for this coming Sunday, albeit with a bit lower confidence in what may happen, but let’s hope we transition out of 2020 with some snowpack building and much needed water reserves for a parched state.

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: Sunny. Snow levels below 7000 feet. Chance of precipitation is 0%. Clear. Snow levels below 7000 feet. Chance of precipitation is 0%. Mostly cloudy. Snow levels below 7000 feet. Chance of precipitation is 5%.
Temperatures: 36 to 42. deg. F. 20 to 26. deg. F. 34 to 40. deg. F.
Mid Slope Winds: West around 15 mph in the morning becoming light. Gusts up to 35 mph. Light winds. Light winds.
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
Wednesday Wednesday Night Thursday
Weather: Sunny. Snow levels below 7000 feet. Chance of precipitation is 0%. Clear. Snow levels below 7000 feet. Chance of precipitation is 0%. Mostly cloudy. Snow levels below 7000 feet. Chance of precipitation is 5%.
Temperatures: 31 to 37. deg. F. 22 to 28. deg. F. 26 to 32. deg. F.
Ridge Top Winds: East 15 to 30 mph with gusts to 45 mph. South around 15 mph with gusts to 25 mph. Northwest around 15 mph with gusts to 25 mph.
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 Avalanche Advisory is provided by the Eastern Sierra Avalanche Center, who is solely responsible for its content.

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