Avalanche Advisory: Sunday - Jan 13, 2019

THIS AVALANCHE ADVISORY EXPIRED ON January 14, 2019 @ 6:38 am
Avalanche Advisory published on January 13, 2019 @ 6:38 am
Issued by Chris Engelhardt - Eastern Sierra Avalanche Center

MODERATE Avalanche Conditions exist in the Upper to Mid Elevations today. Human-triggered avalanches could be possible while Natural Avalanches will be unlikely. Small avalanches in specific terrain or large avalanches in isolated areas could be possible where E-NE winds have developed WIND SLABS and where PERSISTENT SLABS from the January 5/6 storms are overlying weak faceted snow. E-NE winds most likely will have loaded the aspects of W-S-SW-NW-N in the upper to mid elevations. Persistent slabs are residing on NW-N-NE-E-SE at all elevations. Evaluate terrain carefully and use benign test slopes to see if there is reactive conditions in your travel area.

2. Moderate

?

Above Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

2. Moderate

?

Near Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

1. Low

?

Below Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
    Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Wind Slab
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Winds from the E and NE blew yesterday and through the night and potentially redistributed loose snow to a variety of different aspects (NW-W-S-SW-S-SE) than the previous days S-SW flow. Continue to be on the lookout on N-NE-E aspects where windslab may still reside from the previous days Southerly winds. Look for freshly deposited pillows and sections of snow especially on the sunnier aspects of W-SW today. Sunnier skies and solar input could contribute to loosening small panels of snow in extreme and steeper terrain. Be aware of overhead hazards if you’re traveling in tight and steep terrain such as chutes or gullies.

Avalanche Problem 2: Persistent Slab
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Last weekend’s storm (Jan 5-6) laid down a blanket of denser snow that is now consolidating on NW-N-NE-E-SE aspects and is from 50-60cm thick resting on top of soft, collapsible weak layers of facets. The interface between the new thick slab and the old faceted snow is anywhere between 60 to 75cm below the surface and presents a poor upside down structure to our snowpack. It is variable in location and distribution, and presents a worrisome condition that is unpredictable in nature. Unsupported slopes, convex rolls, and extreme terrain will be areas where this persistent slab is possible to be triggered and has the potential to produce larger avalanches. 

advisory discussion

There have been no reports or observations of new avalanche activity since this past Thursday when small loose snow avalanches and associated shallow soft storm slab D1 avalanches were reported in steep N-NE facing terrain from Wednesdays (1/09) 4-8” storm. More interestingly and THANKS to many public observers out there, is the presence of PERSISTENT SLAB conditions and associated whumping and collapsing of the snowpack in the forecast area. (See Observations from 1/12 June Lake Area & 1/12 Bishop Bowl Area).  In general, the interface between our floating slab (35-60cm thick from 1/5-6 storm) and older faceted snow (30-40cm) is around 50 to 60cm below the surface and in many cases there is a dramatic difference in hardness with the newer slab being between 1F-4F and the faceted layer below residing in very loose (F) conditions. These conditions are spatially variable throughout the forecast zone, and seem to be more prevalent at and below tree line where old snow remained sheltered and was allowed to facet and decompose during our relatively cold December temperatures. Although the faceted (F) layer is also present in the alpine it has been observed to be rounding, more compressed, and there have not been any reports of collapsing or avalanches to date. Likely increased wind effects and deeper relative snowpack has contributed to a less sensitive faceted layer in the alpine regions.  WIND SLAB in the region is generally our number one issue and in more extreme and steep terrain as always, backcountry travelers should be on the lookout for pillows or fat looking snow surfaces. The advent of yesterdays and last night’s prevailing Easterly winds will redistribute wind slabs onto more westerly and southerly aspects than has been seen the past few days.

 

Weather and CURRENT CONDITIONS
weather summary

 

A relative quiet day is on tap before we change back to a stormier weather pattern starting Monday.  Sunny skies are forecast today with above freezing temperatures 36F in the mid elevations with 24-30F above 10000ft.  Light to moderate E-SE winds are predicted in the middle elevations with stronger gusts reaching 45mph on the ridge tops.  Cloudier conditions will build again in the area tonight and a chance of snow (2”) is expected for Monday. Chance for snow increases Tuesday with a potential major winter storm still on track for Wednesday-Thursday.  If this culminates we could see our first big natural avalanche cycle and perhaps better coverage throughout the forecast zone.

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: Sunny Clear then becoming mostly cloudy. Chance of precipitation is 5%. Mostly cloudy. Chance of snow. Chance of precipitation is 45%.
Temperatures: 30 to 36. deg. F. 14 to 20. deg. F. 25 to 31. deg. F.
Mid Slope Winds: East to southeast 10 to 15 mph with gusts to 25 mph. Southeast 10 to 20 mph with gusts to 30 mph. Southeast 10 to 20 mph with gusts to 30 mph.
Expected snowfall: 0 in. 0 in. 1 in.
Over 10,000 ft.
Sunday Sunday Night Monday
Weather: Sunny Partly cloudy then becoming mostly cloudy. Chance of precipitation is 5%. Mostly cloudy. Chance of precipitation is 50%.
Temperatures: 24 to 30. deg. F. 9 to 15. deg. F. 18 to 24. deg. F.
Ridge Top Winds: East 15 to 30 mph with gusts to 45 mph. Southeast 15 to 30 mph with gusts to 40 mph. South to southeast 15 to 25 mph with gusts to 35 mph.
Expected snowfall: 0 in. 0 in. 2 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.

ESAC receives support from ...