Avalanche Advisory: Tuesday - Jan 22, 2019

THIS AVALANCHE ADVISORY EXPIRED ON January 23, 2019 @ 6:48 am
Avalanche Advisory published on January 22, 2019 @ 6:48 am
Issued by Chris Engelhardt - Eastern Sierra Avalanche Center

The avalanche danger is CONSIDERABLE at Upper elevations and MODERATE at Middle to Lower elevations today. High winds will transport recent snow and form wind slabs on a variety of aspects. Warming temperatures and sunny skies could also destabilize windslab in specific areas. Persistent slab avalanches remain a problem today.

3. Considerable

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

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.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
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Strong to Extreme Winds have literally blown around the compass rose the past few days in the higher elevations. Southwesterly winds dominated for multiple days and then switched early yesterday to a strong Northerly flow that blew through last night and will continue today. Fresh wind slabs and cornices in mid to upper elevations could be possible on nearly every aspect, so be on the lookout for suspect terrain features-particularly cross loaded gullies, and complicated terrain that may better capture transporting snow. Temperatures are forecast to warm up and the sun is expected to shine today. The advent of increased solar radiation coupled with warmer temps could shake loose newly deposited wind slab or loose deposits of snow. Be aware of isolated areas and extreme terrain features such as chutes and couloirs that funnel loose flowing snow. North winds are particularly troubling as there is a nearly unlimited amount of new softer snow as well as deep residual snowpack to mine, strip and retransport to sunnier aspects. This is the primary reason to keep avalanche danger at CONSIDERABLE today in the alpine environment.

Avalanche Problem 2: Persistent Slab
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Our PERSISTENT SLAB problem is well established throughout the area with weak faceted snow present on a majority of aspects and elevations. We are dealing with a variety of concerns, with basal FACETS and mid-pack persistent grains in the form of surface hoar, melt-freeze layers and faceted crusts.

In the SOUTHERN part of the forecast zone, (Bishop Creek to Rock Creek) the snowpack is typically much shallower averaging from 130-160cm in depth where it is the deepest, (leeward alpine areas likely have more depth, but there are fewer observations). Up until last week’s big storm of Jan 16-17 the snowpack was overall quite minimal with faceted and loose cohesionless snow at the bottom of the pack, if not the entire snowpack in areas. After the storm it remains quite spatially variable with many places harboring thin upside down snowfields that are weak in structure (See 1/18 Bishop Bowl Obs-snow profile). Basal facets are present and on sunny aspects a variety of faceted mid pack crusts exist.

In the NORTHERN part of the forecast zone (Crowley-Mammoth-Virginia Lakes) (limited observations north of June the past few weeks) overall snowpack is generally deeper with depths averaging from 150cm to over 300cm in the loaded alpine areas. Although similar to the south with a snowpack harboring basal facets, the big talking point is that of buried mid pack SURFACE HOAR (See 1/21-Earthquake Dome Obs). This persistent grain type is highly suspected of being responsible for multiple skier triggered avalanches in the Punta Bardini Area (See 1/19 Tele Bowls Obs).

These persistent slabs (residing cohesive slab resting on top of weak persistent grains) can be unpredictable in nature and can propagate over wide distances and run through what is often considered safe terrain. Triggers in the form of a skier or another avalanche can provide just enough added weight to overwhelm the weakness and cause the slab to step down to the weak interface below.  

advisory discussion

Good note to keep in the data bank is our recent history of multiple near misses (see observations page) with skiers/riders triggering significant avalanches and proof of large natural avalanches that occurred during last week’s big storm. The recent storm cycle that has hit a majority of the western US has unfortunately dealt the mountain community with multiple fatalities this past week. Although the snowpack in the Rockies and Intermountain west is much different than ours, it is a solid reminder that avalanches are a constant when it comes to living and recreating in the mountain environment. It is sad to research, but benificial in the long run to learn what we can from these incidents. Avalanche.org posts accident information at https://avalanche.org/avalanche-accidents/

Weather and CURRENT CONDITIONS
weather summary

A sunny day is on tap with much warmer temperatures than the chilly conditions of yesterday. Above freezing temps 35F will hit the low to mid elevations while upper elevations will be in the 27-32F range. Northerly winds with strong ridgetop speeds 30-45mph and extreme gusts 75mph will blow during the early day with anticipated moderation in the afternoon. No precipitation is in the forecast. A sunny and warm week is slated with continued northerly winds at least for the next few days. High pressure and quiet weather is looking to set in through the end of the month. On a good note, our active weather pattern has put snowpack totals to 100-130% of normal throughout the Sierra Nevada thus far this season.

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: Sunny Clear Sunny
Temperatures: 30 to 35. deg. F. 15 to 20. deg. F. 38 to 43. deg. F.
Mid Slope Winds: Northeast 10 to 15 mph with gusts to 50 mph in the morning becoming light. Light winds Light winds
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
Tuesday Tuesday Night Wednesday
Weather: Sunny Clear Sunny
Temperatures: 27 to 32. deg. F. 14 to 19. deg. F. 35 to 40. deg. F.
Ridge Top Winds: North 30 to 45 mph with gusts to 75 mph decreasing to 20 to 30 mph with gusts to 50 mph in the afternoon. North 15 to 25 mph with gusts to 35 mph. Northwest 15 to 25 mph with gusts to 35 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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