Avalanche Advisory: Thursday - Jan 28, 2021

THIS AVALANCHE ADVISORY EXPIRED ON January 29, 2021 @ 6:48 am
Avalanche Advisory published on January 28, 2021 @ 6:48 am
Issued by Chris Engelhardt - Eastern Sierra Avalanche Center

EXTREME AVALANCHE DANGER exists today as a powerful winter storm impacts the Eastern Sierra. Heavy accumulations of new snow and loading southerly winds will build Slabs on All Aspects. Avoid all Avalanche terrain as natural and human triggered avalanches are certain.

5. Extreme

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Above Treeline
Avoid all avalanche terrain.

5. Extreme

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Near Treeline
Avoid all avalanche terrain.

5. Extreme

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Below Treeline
Avoid all avalanche terrain.
    Avoid all avalanche terrain.
Avalanche Problem 1: Wind Slab
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Strong to moderate southerly winds optimal for loading combined with massive amounts of new snowfall (4-6ft+) will be building reactive and deep wind slabs on virtually all aspects and elevations. W-N-E-SE will be aspects of primary concern with guaranteed wind slab development adjacent to ridgeline and terrain features conducive to capturing wind transported snow such as cliff bands, convex rollovers and gullies. Avalanches of all sizes and scope are nearly certain today. Large to very large avalanches have the potential to run into lower terrain where you may normally think you are safe. Avoid all avalanche terrain!

Avalanche Problem 2: Storm Slab
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Incredible amounts of new snow (4-6ft and likely more in some areas) fell Wednesday; snowfall was unrelenting through last night and will continue today. Fresh, sensitive, and unstable storm slabs on All Aspects at All Elevations are guaranteed to be present. In the midst of a storm of this magnitude avalanche conditions will be extremely dangerous as new snow will be looking to adjust its balance in relation to gravity and slope. This means avalanches in all forms, from soft sensitive slabs on virtually any slope with a bit of steepness, to loose dry point releases in very steep terrain.

Avalanche Problem 3: Persistent Slab
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This hefty storm is rapidly loading the shallow and loose-grained snowpack from November and December with a significant amount of weight. W-SE aspects all harbor weak structure from our prolonged drought through the first half of the winter. The rapid loading and large amount of weight in the new snow will likely cause collapse and failure in these old weaker layers. Avalanches originating from fresh unstable wind/storm slab and loose dry will add to the pressure on these weak persistent layers and could cause avalanches to “step down” into the older snowpack causing much bigger and destructive avalanches.

advisory discussion

These are Extreme Conditions; we strongly recommend avoiding all avalanche terrain today.

A few hardy souls tried to go out for some exploratory tours into non-avalanche terrain yesterday and found conditions so deep that travel both up and downhill was virtually impossible. Any slope with a bit of steepness was sensitive and showing signs of instability. Similar conditions will be present today with now even greater depths of new snow.

The risk of deep snow immersion (potentially suffocating if taking a fall or dive into this deep of snow) is a real concern, including for small children and pets falling into depths they may have a very hard time getting out of. Be careful working around buildings where Roof-Avalanches and shedding ice can be a real threat. Please take note of what is above you and try to avoid travelling under roof lines where a snow slide could bury you- even in town!

Trying to get out in the midst of this event is just not worth the Risk vs Reward. The rapid loading of tons of new snow, transporting winds and massive amount of weight added to our weak snowpack are all major red flags. There will be plenty of time to ride once this subsides.

Weather and CURRENT CONDITIONS
weather summary

A blizzard warning is in effect until 10am Friday. This storm has indeed produced heavy snowfall (4-6ft) and liquid water amounts (5.5”+ Snow Water Equivalent) focused on the Mammoth area.  Accumulating snow continued without relent through Wednesday night and is projected to proceed through Thursday with upwards of another 2ft during the day and more accumulation (~6-12”)  tonight. Moderate to Strong Southerly winds will continue in the Upper Elevations with temperatures in the 17-25defgF range. Lower elevations will continue to have milder temperatures (24-30degF) and moderate winds with some gusts reaching 50mph. Things are slated to taper off by Friday morning with light continued snowfall into a less dramatic weekend.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Thursday Thursday Night Friday
Weather: Cloudy. Snow. Snow levels below 7000 feet. Chance of precipitation is 95%. Cloudy. Snow in the evening, then chance of snow after midnight. Snow levels below 7000 feet. Chance of precipitation is 95%. Mostly cloudy. Chance of snow. Snow levels below 7000 feet. Chance of precipitation is 55%.
Temperatures: 24 to 30. deg. F. 11 to 16. deg. F. 21 to 27. deg. F.
Mid Slope Winds: South 15 to 30 mph with gusts to 50 mph. South around 15 mph with gusts to 30 mph. Light winds becoming southwest around 15 mph in the afternoon. Gusts up to 25 mph.
Expected snowfall: 70% probability of 13 to 20 inches. 30% probability of 20 to 25 inches. | SWE = up to 1.45 inches. in. 70% probability of 6 to 12 inches. 30% probability of 3 to 6 inches. | SWE = 0.40-0.65 inch. in. 80% probability up to 2 inches. 20% probability no accumulation. | SWE = less than 0.10 inch. in.
Over 10,000 ft.
Thursday Thursday Night Friday
Weather: Cloudy. Snow. Snow levels below 7000 feet. Chance of precipitation is 95%. Cloudy. Snow in the evening, then snow likely after midnight. Snow levels below 7000 feet. Chance of precipitation is 95%. Mostly cloudy. Snow likely. Snow levels below 7000 feet. Chance of precipitation is 75%.
Temperatures: 17 to 23. deg. F. 6 to 11. deg. F. 13 to 19. deg. F.
Ridge Top Winds: South 30 to 45 mph with gusts to 55 mph decreasing to 25 to 35 mph with gusts to 45 mph in the afternoon. Southwest 15 to 25 mph. Southwest around 15 mph with gusts to 25 mph.
Expected snowfall: 80% probability of 17 to 25 inches. 20% probability of 20 to 30 inches. | SWE = 1.25-1.75 inches. in. 70% probability of 6 to 12 inches. 30% probability of 4 to 8 inches. | SWE = 0.55-0.80 inch. in. 80% probability up to 2 inches. 20% probability no accumulation. | SWE = up to 0.15 inch. 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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