Avalanche Advisory: Wednesday - Feb 3, 2021

THIS AVALANCHE ADVISORY EXPIRED ON February 4, 2021 @ 6:55 am
Avalanche Advisory published on February 3, 2021 @ 6:55 am
Issued by Chris Engelhardt - Eastern Sierra Avalanche Center

CONSIDERABLE AVALANCHE DANGER exists today for fresh Wind Slab and Cornice formation. Southerly winds will continue to impact the Eastern Sierra and transport snow to leeward aspects of W-NW-N-E-SE at All Elevations. Natural Avalanches are possible and human-triggered avalanches likely especially adjacent to ridgeline and complex terrain conducive to capturing wind transported snow. Conservative decision making will be key today.

*Join ESAC Forecaster Steve Mace TONIGHT for a free virtual Avalanche Awareness Event Wed Feb 3rd (6-7:30pm): Avalanches 101.  Click here to view the recorded Zoom Event!

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.

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: Wind Slab
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Strong to extreme southerly winds combined with plenty of fresh snow from last weeks big dump will continue to build reactive wind slab on W-NW-N-E-SE aspects at all elevations today. Slopes adjacent to and underneath leeward ridgelines and cliffy features will be of most concern. Pay attention to blowing snow, fresh cornice formation and fat looking snow deposits, pillows and wind ribbons. Features conducive to capturing wind transported snow such as cliff bands, convex roll overs and gully features will require cautious route-finding. Triggering a fresh wind slab slide may produce enough weight to trigger an even bigger Persistent slab to step down to weak basal snow resulting in large avalanches.

Avalanche Problem 2: Cornice
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There has been consistent SW wind for multiple days and it significantly ramped up last night and is slated to be extreme for a majority of Wednesday. W-NW-N-E-SE aspects adjacent to ridgeline are of primary concern. Cornice failures and subsequent wind slab avalanches have already been observed throughout the Mammoth area the past few days and will be a major feature to be on the lookout for today. Give these wave like features adjacent to ridgeline a wide margin while travelling on top of ridges and avoid being underneath them at any point today. Cornices are consistently one of the main killers of mountaineers and skiers and can be very reactive when actively forming, which will be the case during today’s wind event.  

Avalanche Problem 3: Persistent Slab
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We now have a robust slab nearly 3-4ft deep in a majority of northerly-easterly terrain residing on a shallow and loose-grained snowpack from November and December. This issue is of most concern on N-E aspects, but we are not ruling out the broader aspect range of W-SE aspects due to weak structure existing everywhere that harbored snow from Nov/Dec. This basic upside down structure with a heavy slab sitting on top of weak wafer like basal snow likely contributed to a large Skier-triggered slab avalanche in Punta Bardini this past Saturday. Areas of particular concern are steep (>30deg), unsupported slopes, and areas with lots of rock and cliffs that harbor cavities and weaker more faceted basal depth hoar and loose grained snow.

Weather and CURRENT CONDITIONS
weather summary

A wind advisory is in effect today until 4pm with SW winds continuing to strafe the Sierra with the highest velocities during morning hours (40-55mph, gusts to 90mph). Velocities should decrease a bit in the afternoon under partly cloudy to sunny conditions today. Temperatures should remain below freezing for most elevations with 16-24degF in the alpine and up to 31degF in the lower mountains. Winds should calm down tonight and revert to a NW flow with a calmer sunny day Thursday.

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 5%. Clear then becoming partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 0%. Sunny. Snow levels below 7000 feet. Chance of precipitation is 0%.
Temperatures: 23 to 31. deg. F. 7 to 12. deg. F. 31 to 37. deg. F.
Mid Slope Winds: Southwest 25 to 40 mph shifting to the west 20 to 30 mph in the afternoon. Gusts up to 60 mph. Northwest around 15 mph. Gusts up to 35 mph. Light winds.
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
Wednesday Wednesday Night Thursday
Weather: Partly cloudy then becoming sunny. Snow levels below 7000 feet. Chance of precipitation is 5%. Clear. Snow levels below 7000 feet. Chance of precipitation is 0%. Sunny. Snow levels below 7000 feet. Chance of precipitation is 0%.
Temperatures: 16 to 24. deg. F. 3 to 8. deg. F. 26 to 32. deg. F.
Ridge Top Winds: Southwest 40 to 55 mph decreasing to 30 to 45 mph in the afternoon. Gusts up to 90 mph. Northwest 15 to 25 mph. Gusts up to 55 mph decreasing to 35 mph after midnight. North 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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