Avalanche Advisory: Sunday - Feb 3, 2019

THIS AVALANCHE ADVISORY EXPIRED ON February 4, 2019 @ 6:55 am
Avalanche Advisory published on February 3, 2019 @ 6:55 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center

Avalanche danger is HIGH today.  Over 4ft of snow has fallen at many higher elevation areas in less than 36 hours, with an additional foot likely today.  SW winds have increased significantly even at lower elevations.  Large deadly avalanches are very likely.  Travel in or under 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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SW winds have increased substantially from yesterday.  Low to mid elevations were relatively calm yesterday, but that has changed. 65mph gusts are expected at mid-elevations, and 90mph gusts over ridge-tops.  With tons of new snow ripe for transport and more snow falling, large sensitive wind slabs will be widespread in all areas where terrain results in decreased wind speeds and deposition.  The leeward side of ridges, sidewalls of gullies, the edges of forests and across open slopes will be the most obvious places to find these wind slabs.  Remember winds can deposit snow at far greater rates than it can fall from the sky!  Avoid being on or under slopes steeper than 30° with denser wind deposited snow.

Avalanche Problem 2: Storm Slab
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Intense snowfall over the past 36 hours, with an additional foot likely today, means dangerous storm slabs in all areas protected from the wind.  Significant natural and human triggered storm slab avalanching was reported yesterday in the Sherwins. The depth of potential storm slabs was fairly easy to recognize yesterday, but now as some settlement has occurred and depths have increased, it will be much trickier to judge avalanche potential.  Significant Loose Dry surface sloughing will be very likely, but don’t let that fool you into thinking that what is slightly more dense deeper down can’t be triggered resulting in a large and dangerous storm slab avalanche.  Fragile surface hoar was found in various areas prior to the storm, which could lead to avalanches propagating farther across a slope than expected, as well as being remotely triggered.  Travel on or under slopes greater than 30° is NOT recommended.  

Avalanche Problem 3: Persistent Slab
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Various layers of buried weaker snow have been found throughout the forecast area. Although these have been gaining strength and have not been concerning over the past week, the intense new snow load will likely reawaken some of these layers, particularly where shallower snow packs exist.  The force of a smaller wind slab or storm slab avalanche, or simply the heavy new load of snow alone, could result in larger avalanches than expected failing on these deeper weak layers of snow.  Give suspect slopes a wide berth especially in areas with known shallower snowpacks.  

advisory discussion

Although snowfall intensities will be less today, the snow that has already fallen and the increased SW winds even at lower elevations will make for even more dangerous avalanche conditions today than yesterday.  Terrain that could be potentially managed yesterday will be much harder to manage safely today.  Besides avalanches, be aware of the very real dangers that exist with deep snow emersion! Don’t get stuck head first in a tree-well without a partner very nearby to help save you.  And watch out in town around buildings with heavy snow-loads hanging on roofs.

recent observations

-2/2 - Mammoth - Sherwins: Storm slab avalanche activity. 

-2/2 - Mammoth - Punta Bardini: Shooting cracks, snowfall, increasing slabby conditions and concern.

-2/2 - Bishop Creek - Aspendell: New snow, weather.

Low to mid-mountain storm snowfall totals since beginning less than 36hours ago:

42.5” snow (4.75”SWE) – 9000’ on Mammoth Mtn

40+” snow at 9150’ on June Mtn

30” snow at 9650’ in Big Pine Creek

14” at 9600’ in Rock Creek

20” at 9400’ in Virginia Lakes

Weather and CURRENT CONDITIONS
weather summary

*WINTER STORM WARNING IN EFFECT FROM NOW THRU 4PM TUESDAY 

We are in the middle of the biggest storm cycle of the season, with another 1ft+ of snowfall likely today, and an additional 1-2ft tonight.  SW winds have increased significantly since yesterday and will remain strong thru Monday, with blowing snow at low elevations and gusts reaching 90mph over ridge-tops.  Temperatures will be slightly cooler than yesterday and will continue to drop thru the week. 1-2ft of snow is expected for every 12hour period after today thru Tuesday morning.   

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Sunday Sunday Night Monday
Weather: Cloudy. Snow. Cloudy. Snow. Cloudy. Snow.
Temperatures: 26 to 34. deg. F. 19 to 24. deg. F. 22 to 30. deg. F.
Mid Slope Winds: Southwest 20 to 35 mph with gusts to 65 mph. Southwest 15 to 30 mph with gusts to 65 mph. South 20 to 35 mph with gusts to 65 mph.
Expected snowfall: 80% probability of 7 to 13 inches. 20% probability of 12 to 18 inches. | SWE = up to 0.70 inch. in. 70% probability of 11 to 20 inches. 30% probability of 21 to 29 inches. | SWE = 0.60-0.85 inch. in. 70% probability of 10 to 18 inches. 30% probability of 18 to 24 inches. | SWE = 0.55-1.00 inch. in.
Over 10,000 ft.
Sunday Sunday Night Monday
Weather: Cloudy. Snow. Cloudy. Snow. Cloudy. Snow.
Temperatures: 19 to 24. deg. F. 13 to 18. deg. F. 16 to 21. deg. F.
Ridge Top Winds: Southwest 40 to 60 mph with gusts to 90 mph. Southwest 30 to 45 mph with gusts to 70 mph increasing to 45 to 60 mph with gusts to 95 mph after midnight. Southwest 40 to 60 mph with gusts to 90 mph.
Expected snowfall: 80% probability of 8 to 13 inches. 20% probability of 13 to 19 inches. | SWE = 0.55-0.80 inch. in. 70% probability of 13 to 24 inches. 30% probability of 24 to 35 inches. | SWE = 0.55-1.05 inches. in. 70% probability of 12 to 24 inches. 30% probability of 24 to 32 inches. | SWE = up to 1.15 inches. 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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