Avalanche Advisory: Monday - Jan 14, 2019

THIS AVALANCHE ADVISORY EXPIRED ON January 15, 2019 @ 5:06 am
Avalanche Advisory published on January 14, 2019 @ 5:06 am
Issued by Chris Engelhardt - Eastern Sierra Avalanche Center

MODERATE Avalanche Conditions exist in the Upper and Middle Elevations today. Human-triggered avalanches and Natural Avalanches will be possible today. Small avalanches in specific terrain or large avalanches in isolated areas could be possible where SE-E-NE winds have developed WIND SLABS and loaded new LOOSE DRY snow. Easterly winds combined with new light snow today will load W-NW-N-NE-E aspects in the upper to middle elevations. PERSISTENT SLABS from the January 5/6 storms are overlying weak faceted snow and are residing on NW-N-NE-E-SE at all elevations. Identify changing snow conditions, features of concern and evaluate terrain carefully in your trip plans and execution today.

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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Prevailing Easterly winds blew at moderate to strong speeds throughout the day yesterday with a bit of a lull early this morning. Wind transported snow pluming off the high peaks was visible (see 1/13 Mammoth Area-Laurel Mtn Obs) and there was one report of a skier triggered wind slab in the Mt. Morrison area (see 1/13 Convict Area Obs).  SE winds are predicted to pick up and blow today at perfect loading speeds in the 15-25mph range. These Moderate winds moving existing light snow on the ground combined with today’s light accumulations could really load up the W-NW-N-NE-E aspects. With overcast conditions and potentially reduced visibility, be aware of what terrain and loaded slopes or terrain features reside above you or could affect your intended travel and descent routes.

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. 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. (See 1/12 June Lk Obs). 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 or observations of avalanches sliding on this slab/facet interface as of yesterday, but with limited information in our large forecast zone, travelers should be aware of this condition and perform their own investigations.

Avalanche Problem 3: Loose Dry
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The light snow from 1/09 has been great skiing, but also has been sluffing in steep and extreme terrain. Today and tonight’s additional light snowfall and SE winds will further increase the potential for light dry point releases and skier triggered sluffs. Be aware of this with your line choice and up-route travel plans. Again W-NW-N-NE-E aspects will be the slopes of most concern.

advisory discussion

New light snow accumulations combined with the Moderate SE winds will be the main driver of potential avalanche activity today.  Wise terrain choice and identifying where potential hazards lurk will be the key with reduced visibility and blowing snow. We are on the cusp of a large storm cycle, with plenty of good skiing in the near future, so keeping track of changing conditions and the differences in how slopes look now compared to a few days out will be great information in the data bank to inform oneself on how winds and the mountain environment captured new snow loads.

In regards to our PERSISTENT SLAB, 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 on this layer to date. Likely increased wind effects and deeper relative snowpack has contributed to a less sensitive faceted layer in the alpine regions.   

Weather and CURRENT CONDITIONS
weather summary

Mostly cloudy conditions with light snow are on tap for today. Winds will be out of the SE at light to moderate (15-30mph) speeds with stronger 40mph gusts over ridge tops for this afternoon. Snow accumulations could reach 1-2” at lower elevations with potentially up to 4” for the Sierra Crest during the day. Snow is expected to continue into tonight with an additional 2” at 8000ft and up 2- 6” in the high country tonight on the high end. Snow is likely to continue with greater accumulations (additional 3-5” up high) Tuesday with Southerly winds. Light snow through today and tomorrow combined with cold temperatures and loading SE winds could produce much deeper snow totals in places if the forecast pans out. The main event is still slated to take place Wednesday night into Thursday with 2-4’ of snow potentially hitting the Sierra Crest.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Monday Monday Night Tuesday
Weather: Mostly Cloudy Chance of precipitation is 50%. Cloudy. Snow likely. Chance of precipitation is 70%. Cloudy. Chance of snow in the morning, then snow likely. Chance of precipitation is 40% increasing to 70% in the afternoon.
Temperatures: 24 to 30. deg. F. 17 to 22. deg. F. 26 to 32. deg. F.
Mid Slope Winds: Southeast 10 to 15 mph with gusts to 35 mph. Southeast 10 to 15 mph with gusts to 35 mph. South 10 to 15 mph with gusts to 35 mph.
Expected snowfall: 1-2 in. 2-4 in. 2-4 in.
Over 10,000 ft.
Monday Monday Night Tuesday
Weather: Mostly cloudy. Light snow developing in the afternoon. Chance of precipitation is 70%. Cloudy. Snow in the evening...then a chance of snow showers. Chance of precipitation is 80% in the evening...then 50%. Cloudy. A chance of snow in the morning...then snow likely. Chance of precipitation is 40% in the morning increasing to 75%.
Temperatures: 19 to 25. deg. F. 12 to 17. deg. F. 19 to 25. deg. F.
Ridge Top Winds: Southeast 15 to 25 mph. Gusts up to 30 mph increasing to 40 mph in the afternoon. South 15 to 30 mph with gusts to 40 mph. South 15 to 30 mph with gusts to 40 mph.
Expected snowfall: 2-4 in. 2-6 in. 3-8 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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