Avalanche Advisory: Sunday - Mar 11, 2018

THIS AVALANCHE ADVISORY EXPIRED ON March 12, 2018 @ 6:47 am
Avalanche Advisory published on March 11, 2018 @ 6:47 am
Issued by Clancy Nelson - Eastern Sierra Avalanche Center

The avalanche danger today is MODERATE at all elevations. Small wet avalanches may be possible in specific areas by this afternoon. Warm sunny slopes where the snow becomes saturated, and steep rocky terrain, will be of most concern. While unlikely, an isolated large deep slab avalanche is not impossible on northerly slopes, especially between 9,000’ and 10,500’ where the snowpack is still weak. Do your own stability assessment to test the weak layers in your area.

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.

2. Moderate

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Below Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
    Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Loose Wet
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If the sun comes out this afternoon and temperatures rise to the 40s, wet snow instabilities may become a hazard. Rollerballs and small point releases originating from rocky areas and vegetation are a sign that the snow is becoming saturated with water and weaker. Lower elevations and southerly aspects are most likely to have wet avalanches, but E, N, and W aspects may also show signs of thawing below about 10,000’.

Avalanche Problem 2: Deep Slab
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The deeply buried layers of weak sugar snow have not gone away, they can be found between 60 and 150cm below the surface on northerly slopes. Tests performed on these layers in the Mammoth area continue to indicate that they can fail under stress. But, the last time whumphing in this layer was experienced was on 3/6. An avalanche caused by slope-wide collapse in these faceted snow grains seems to be harder to trigger. But not impossible. It’s a low likelihood-high consequence situation. Big sudden stresses on these layers, especially near trigger points, could cause a large avalanche. Landing a big jump in an area where the weak layers are closer to the surface is an example of the kind trigger that might get you into trouble. Digging into the snow where you want to play is the best way to know what these layers are doing.

advisory discussion

Snow showers forecasted for yesterday afternoon and overnight were underwhelming. An inch or two of snow fell in the northern half of the forecast area, with up to 3 inches in the mountains outside of Bishop. But these kinds of minor precipitation events are typical for spring. Mostly sunny skies, warm temperatures, and light winds today may allow the surface snow to warm through. Small wet avalanches will become increasingly possible throughout the day. Watch for rollerballs coming down the slope around you, especially in steep rocky terrain where the sun is most intense. Small point releases are an indication that larger avalanches are possible. Timing your day to be off of suspect slopes before before they thaw too deeply is the easiest way to avoid the problem.

All season we have been discussing and tracking layers of persistent, weak, sugary snow (facets) that developed in areas that had shallow snow coverage prior to the storm that began March 1st. That event finally dropped enough snow to act as a cohesive slab overlying the persistent weak layers and some very large and destructive avalanches occurred through March 4th. While the threat of failure in the buried facets seems to be improving, deeply buried weaknesses are notoriously hard to predict. The last reported collapse of the buried weak layers was on the 6th, but snowpack tests as recently at yesterday have continued to indicate that failure in these sugary snow grains is not impossible. With few observations, we don’t entirely know what to expect from these layers, especially outside of Mammoth. So doing your own stability assessment is the best way to see what these layers are doing in your area. Warm temperatures will most likely allow the snow to gain strength, but slowly. We will have to monitor as temperatures dip below normal again later this week. More precipitation Tuesday through the weekend may create additional stress on the weak snowpack.

Weather and CURRENT CONDITIONS
weather summary

Drier conditions are expected today into Monday. Light winds and mostly sunny skies. Temperatures will be near, or slightly above, average falling below average late in the week.

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 then becoming partly cloudy. Partly cloudy then becoming mostly cloudy. Partly cloudy then becoming sunny.
Temperatures: 41 to 47 deg. F. 25 to 30 deg. F. 43 to 49 deg. F.
Wind Direction: Light winds. Light winds. S
Wind Speed: Light winds. Light winds. Light winds becoming 10 to 15 mph with gusts to 25 mph in the afternoon.
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
Sunday Sunday Night Monday
Weather: Mostly cloudy then becoming partly cloudy. Partly cloudy then becoming mostly cloudy. Partly cloudy then becoming sunny.
Temperatures: 35 to 40 deg. F. 22 to 28 deg. F. 36 to 41 deg. F.
Wind Direction: Light winds. S S
Wind Speed: Light winds. Light winds becoming 10 to 15 mph with gusts to 25 mph after midnight. 15 to 20 mph with gusts to 30 mph.
Expected snowfall: 0 in. 0 in. 0 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 Snowpack Summary is provided by the Eastern Sierra Avalanche Center, who is solely responsible for its content.

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