Avalanche Advisory: Friday - Jan 29, 2021

THIS AVALANCHE ADVISORY EXPIRED ON January 30, 2021 @ 6:24 am
Avalanche Advisory published on January 29, 2021 @ 6:24 am
Issued by Steve Mace - ESAC

HIGH avalanche danger exists on all aspects and at all elevations today. Natural and human triggered avalanches remain very likely. Travel in, near, or underneath avalanche terrain is NOT recommended.

4. High

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Above Treeline
Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.

4. High

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Near Treeline
Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.

4. High

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Below Treeline
Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
    Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
Avalanche Problem 1: Wind Slab
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Heavy snowfall and strong to extreme SW winds over the last 72 hr have created dangerous wind slab conditions. While we expect to see wind speeds drop this morning it is likely they will remain well within the transportable range today, particularly at higher elevations.  This means we may see continued slab development even as the current storm system moves out of the area, particularly if wind speeds outperform the forecast. W-N-E-SE aspects will be most problematic today. Be suspect of terrain features that encourage drifting such as the leeward sides of ridgelines, gully features, and cross-loaded depressions.  Large to very large Natural and Human triggered avalanches are likely today. Avalanches may run long distances and into lower angle, or treed terrain you may typically think of as “safe”. Look for signs of recent wind loading including blowing snow, recent cornice development, and large pillow-like drifts. Be cognizant of what is above you today. Travel in, near, and below avalanche terrain is not recommended.

Avalanche Problem 2: Storm Slab
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Storm totals over the past 72 hr have been mind-blowing. Just under 100” of snow has been recorded in the Mammoth area since the beginning of this storm and totals are likely higher along the crest. While snow totals are significantly less in the southern part of the forecast area make no mistake, this has been a rapid and extreme loading event. It will take some time for this new snow to settle and gain cohesion. Expect storm instabilities ranging from large point release avalanches to very large storm slabs to be sensitive today. Avoid being on or under terrain over 30° today and be cognizant of your exposure to terrain features that increase the consequences of an avalanche. This may include exposed areas under rooflines in town. Be wary of overhead hazards today and avoid being in or underneath avalanche terrain.

Avalanche Problem 3: Deep Slab
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Prior to this major winter storm, forecasters were tracking on the weak faceted base to our snowpack. While we had begun to see some signs of healing in these lower weak layers in some areas, in others we continued to observe weak structure and propagation propensity. Our recent rapid loading event may have already stressed these lower weak layers past their breaking point, but it will be important to keep this poor structure in mind as the snow begins to settle. An avalanche occurring on these deeper weak layers is likely to be full depth and has the potential to be very large and destructive.

advisory discussion

As the dust settles (or in this case the snow) and we all dig out from this major winter storm it will be important to take stock of things. Patience is key. Travel in avalanche terrain is not recommended today. It will be a long winter season and we will have plenty of time to get out and make some turns once the danger subsides. 
In addition to very dangerous avalanche conditions today, Backcountry travel remains very difficult and the risk of deep snow immersion is real. An otherwise benign fall could lead to suffocation in our deep unconsolidated snowpack. This is particularly true for small children and pets who may have more difficulty getting up and out. Be cautious even at the sledding hill or in the back yard. In addition, there is still a risk of roof avalanches in town today. Several roofs slid naturally yesterday, and some were certainly large enough to bury an unsuspecting human.

 

recent observations
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1/28- Mammoth Area- Large roof avalanche in a residential area.

1/28- Mammoth Area- Large roof avalanche in the Vons complex

1/28- Large natural and explosive triggered avalanches reaching highway 395

1/27- Mammoth Area- Difficult travel condition, sensitive storm instabilities in the Sherwin’s.

1/27- Mammoth Area- New, snow, difficult travel, surface instabilities at Punta Bardini

1/27- Bishop Creek- Snow conditions

1/27- Bishop Area- Snow conditions in west Bishop

Weather and CURRENT CONDITIONS
weather summary

Expect mostly clouds skies, cold temperatures, and light to moderate winds out of the southwest today as this major winter storm moves out of the area. Light precipitation may continue through the day but accumulation is only expected to be 2-4”.

We can expect a few days of quieter weather over the weekend as we dig ourselves out of this most recent storm. But don't get too comfortable, another major winter storm is expected to move into the area early next week.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Friday Friday Night Saturday
Weather: Mostly cloudy. Chance of snow through the day. Snow levels below 7000 feet. Chance of precipitation is 80%. Clear then becoming partly cloudy. Snow levels below 7000 feet. Sunny. Snow levels below 7000 feet.
Temperatures: 20 to 28. deg. F. 7 to 12. deg. F. 27 to 33. deg. F.
Mid Slope Winds: Light winds becoming west around 15 mph in the afternoon. Gusts up to 25 mph. Southwest around 15 mph with gusts to 25 mph. Light winds.
Expected snowfall: 80% probability up to 3 inches. 20% probability 3 to 5 inches . | SWE = 0.10-0.20 inch. in. 0 in. 0 in.
Over 10,000 ft.
Friday Friday Night Saturday
Weather: Mostly cloudy. Chance of snow through the day. Snow levels below 7000 feet. Chance of precipitation is 80%. Partly cloudy. Snow levels below 7000 feet. Partly cloudy then becoming sunny. Snow levels below 7000 feet.
Temperatures: 12 to 20. deg. F. 3 to 8. deg. F. 21 to 27. deg. F.
Ridge Top Winds: Southwest around 15 mph with gusts to 25 mph. Southwest around 15 mph with gusts to 25 mph. West around 15 mph. Gusts up to 25 mph in the morning.
Expected snowfall: 80% probability up to 4 inches. 20% probability 4 to 6 inches. | SWE = 0.15-0.20 inch. 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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