Avalanche Advisory: Sunday - Jan 6, 2019

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THIS AVALANCHE ADVISORY EXPIRED ON January 7, 2019 @ 6:59 am
Avalanche Advisory published on January 6, 2019 @ 6:59 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center

CONSIDERABLE avalanche danger will exist throughout today. 12-18”+ of fresh snow and EXTREME SW winds will continue to build dangerous sensitive wind slabs at all elevations on NW-N-E-SE facing slopes with exposure to wind.  Human triggering of storm slab avalanches will be possible as well on the limited slopes that are sheltered from these strong winds.  Cautious route finding and conservative decision making will be essential to avoid being on or under freshly loaded terrain.

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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Human triggered wind slab avalanches will be likely, and natural triggering will be possible throughout today.  12-18” of snow fell yesterday afternoon through early this morning, with another 6-8” possible this afternoon before dark, and another 1.5ft+ possible tonight.  SW winds are already reaching 100mph over ridge tops, and are expected to reach over 125mph by tonight, and even into the 100mph range at lower elevations.  Few areas will be left that aren’t affected by these EXTREME winds.  Denser wind deposited snow will likely exist on leeward slopes that face NW-N-E-SE, especially below ridgelines, the sidewalls of gullies and in other terrain where topography decreases wind-speeds resulting in deposition.  Even small slopes can be dangerous if they end in a terrain trap.  Watch for shooting cracks from your skis, and avoid being on or under slopes >30 degrees where wind is depositing snow. 

Avalanche Problem 2: Storm Slab
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Significant new snowfall will make human triggering of soft lower density storm slab avalanches possible in the most sheltered forested terrain at low to mid elevations. Watch for steep convex rolls as likely trigger points, shooting cracks as a sign of instability, and be aware that even small slopes can be dangerous that end in terrain traps. Underlying loose facets or smooth melt-freeze crusts will make it harder for new storm slabs to bond to the old snow.  Loose snow sloughs could also pose a threat of carrying a rider into undesirable terrain.

advisory discussion

Loose faceted snow has been found throughout our upper snowpack in recent days, whether it is just below some older wind slabs, or at the old snow surface proper in sheltered areas.  This will make it harder for new snow to bond to the old snow, and could lead to greater propagation of fractures and larger avalanches than may be expected.  While surface hoar formation was found to be widespread last week, most of these delicate feather formations were observed to be breaking down or destroyed by sun and winds prior to being buried by the recent snow.  Still, there is a small possiblity that in isolated areas some surface hoar may have persisted and gotten buried.  Avalanche triggering would be especaillyy sensitive in such an area.  A rising snow-level tonight will likely lead to more dense snow being deposited on less dense snow (an upside down snowpack), which is a recipe for more dangerous avalanche conditions tonight and tomorrow.

recent observations
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-1/5 - Mammoth - Sherwins: Afternoon new snow, facets

-1/4 - VA Lakes - Red Lake Bowl: Areas of surface hoar

Weather and CURRENT CONDITIONS
weather summary

The first of a series of storms dropped 12-18” of fresh snow between noon yesterday thru early this morning.  Expect a lull in snowfall this morning before the next storm rolls in late morning through late tonight.  WINTER STORM and HIGH WIND WARNINGS are in effect from 3pm today thru 4am tomorrow morning.  6-8” of additional snow is possible before dark, with another 1.5ft+ possible in favored locations tonight.  Strong SW winds will be on the increase throughout today, reaching EXTREME speeds of up to 100mph at lower elevations, and over 120mph over ridge-tops tonight.  Of note, snow level will be on the rise during this next storm likely reaching 7,000’ before snowfall tapers off late tomorrow morning.  Temperatures will be quite warmer for Monday, reaching near freezing at 10,000’. 

Another storm is expected for Tuesday night into Wednesday.

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: Mostly cloudy. Chance of snow in the morning, then snow in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 65%. Cloudy. Snow. Snow levels below 7000 feet. Chance of precipitation is 80%. Mostly cloudy. Snow showers likely. Snow levels below 7000 feet increasing to 7000 feet in the afternoon. Chance of precipitation is 65%.
Temperatures: 24 to 30. deg. F. 21 to 26. deg. F. 34 to 40. deg. F.
Mid Slope Winds: Southwest 15 to 25 mph. Gusts up to 40 mph increasing to 75 mph in the afternoon. Southwest 35 to 55 mph with gusts to 100 mph. Southwest 30 to 45 mph with gusts to 85 mph decreasing to 15 to 30 mph with gusts to 60 mph in the afternoon.
Expected snowfall: 80% probability of 2 to 6 inches. 20% probability of 6 to 10 inches. | SWE = up to 0.25 inch. in. 70% probability of 10 to 18 inches. 30% probability of 18 to 24 inches. | SWE = 0.60-0.85 inch. in. 90% probability of 2 to 4 inches. 10% probability of 4 to 6 inches. | SWE = up to 0.15 inch. in.
Over 10,000 ft.
Sunday Sunday Night Monday
Weather: Mostly cloudy. Snow. Snow levels below 7000 feet. Chance of precipitation is 85%. Cloudy. Snow. Snow levels below 7000 feet. Chance of precipitation is 95%. Mostly cloudy. Snow showers likely. Snow levels below 7000 feet increasing to 7000 feet in the afternoon. Chance of precipitation is 65%.
Temperatures: 17 to 22. deg. F. 15 to 20. deg. F. 26 to 31. deg. F.
Ridge Top Winds: Southwest 20 to 30 mph with gusts to 50 mph increasing to 30 to 45 mph with gusts to 85 mph in the afternoon. Southwest 55 to 70 mph becoming west and increasing to 70 to 80 mph after midnight. Gusts up to 125 mph. Southwest 45 to 65 mph with gusts to 110 mph decreasing to 30 to 45 mph with gusts to 70 mph in the afternoon.
Expected snowfall: 80% probability of 2 to 6 inches. 20% probability of 6 to 10 inches. | SWE = up to 0.30 inch. in. 70% probability of 10 to 18 inches. 30% probability of 18 to 26 inches. | SWE = 0.60-1.10 inches. in. 90% probability of 2 to 4 inches. 10% probability of 4 to 6 inches. | 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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