Avalanche Advisory: Saturday - Jan 12, 2019

THIS AVALANCHE ADVISORY EXPIRED ON January 13, 2019 @ 6:26 am
Avalanche Advisory published on January 12, 2019 @ 6:26 am
Issued by Chris Engelhardt - Eastern Sierra Avalanche Center

MODERATE avalanche conditions exist today.  Natural avalanches will be unlikely; while human-triggered avalanches will be possible today. Small avalanches in specific terrain or large avalanches in isolated areas could be possible where SW winds have developed WIND SLABS and where PERSISTENT SLABS from the January 5/6 storms are overlying weak faceted snow. Terrain most likely to be loaded from the S-SW winds will be aspects of W-NW-N-NE-E in the upper to middle elevations today. Persistent slabs are residing on NW-N-NE-E-SE at all elevations. Stick to the basics of evaluating snow and terrain carefully while looking for signs of instability such as shooting cracks or whumping and collapsing of the snowpack

2. Moderate

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

2. Moderate

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

1. Low

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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
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Although SW winds started easing off yesterday evening and remained calm through last night, they did blow at moderate speeds and changed directions blowing from the E additionally yesterday. Wind speeds in the high teens to mid-20mph are perfect for transporting snow and loading up terrain that is conducive to capturing snow. Residing light surface snow from Wednesday’s storm was visibly still being moved across the landscape yesterday. Be especially vigilant in complex or extreme alpine terrain where even a small amount of dislodged snow could cause dire consequences.

Avalanche Problem 2: Persistent Slab
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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. This 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. There have not been any reports nor observations of avalanches propagating and running on this slab/facet interface, but with limited information and a big area with new terrain opening for exploration, travelers should be wary of this condition and perform their own stability investigations. A significant collapse of the snowpack and vertical displacement was observed in NW trees at 10300ft (See 1/11 Convict Drainage Observation).

advisory discussion

Although avalanche conditions have moderated, the snowpack exists today in a much more complex state than it did before last weekend’s big storm. Wind slabs are bonding to old snow surfaces, but present hazard on a variety of aspects up high. The persistent slab distribution across the range will need to continue to be monitored to see if the snow pack settles and adjusts or remains upside down in nature. A big storm this coming week could very well flesh out some of these issues or present bigger problems if the weak faceted snow remains in place in the lower stratigraphy of the snowpack.

 

Weather and CURRENT CONDITIONS
weather summary

 

A cloudy day is predicted with light winds from the SE and temperatures in the mid-20sF for the upper elevations and a bit above freezing for the mid to lower elevations. Temperatures look to cool off quite a bit tonight with clear skies and single digit to teens temps above 10000ft. Sunday should be sunny and again calmer with light SE Winds. A series of storms is on the horizon with good potential to bring periods of snow to the Sierra for Tuesday through Thursday.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Saturday Saturday Night Sunday
Weather: Mostly cloudy Clear Sunny
Temperatures: 30 to 36. deg. F. 12 to 18. deg. F. 29 to 35. deg. F.
Mid Slope Winds: Southeast to south 10 to 15 mph with gusts to 25 mph. Southeast to south 10 to 15 mph. Southeast 10 to 15 mph with gusts to 30 mph.
Expected snowfall: No accumulation. | SWE = none. in. No accumulation. | SWE = none. in. No accumulation. | SWE = none. in.
Over 10,000 ft.
Saturday Saturday Night Sunday
Weather: Mostly cloudy Clear Sunny
Temperatures: 23 to 28. deg. F. 6 to 12. deg. F. 22 to 28. deg. F.
Ridge Top Winds: East to southeast 10 to 20 mph with gusts to 30 mph. East 15 to 25 mph. Southeast 15 to 25 mph with gusts to 35 mph.
Expected snowfall: No accumulation. | SWE = none. in. No accumulation. | SWE = none. in. No accumulation. | SWE = none. 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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