THIS AVALANCHE ADVISORY EXPIRED ON March 19, 2018 @ 6:53 am
Avalanche Advisory published on March 18, 2018 @ 6:53 am
Issued by George Halcom - Payette Avalanche Center
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Over a foot of new snow combined with winds have created Considerable avalanche hazard. Wind and storm slabs are not bonding well, but resting on slick crusts. Lingering persistent weak layers are buried 2 to 4 feet below the surface, and are mixed into layers of crusts, graupel, and facets.  Natural avalanches are possible, and Human triggered avalanches are likely today. 

How to read the advisory


  • Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Storm Slab
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The new snow over the last few days came in initially dense, and later lightened up. The denser snow created soft storm slabs that are not bonding well to the old snow surface that developed into a crust, and more pronounced and slicker on aspects that are tilted towards the Sun. Northern aspects stayed a little cooler during last weeks warm up and developed a less stout/thick crust and showed better signs of bonding. Adding almost a foot of new snow today, we could likely see some avalanches go naturally. Human triggered avalanches will be possible, especially on steep solar effected aspects. Avoid steep terrain that is exposed,above cliff bands, terrain traps, or slopes that come to an abrupt end in trees or rocks, and use good, cautious travel protocols today. Yesterday, we observed a couple natural storm slabs that pulled out on the steep North face of Jug Mountain above Louie Lake.

 

Avalanche Problem 2: Wind Slab
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The last couple days have given us a gift of light snow with just enough winds to form wind slabs in exposed, and lee terrain. The wind slabs that are of most concern would be the ones that are resting on crusts that developed from the Sun last week, and are not bonded well.

Yesterday we were able to easily trigger a wind slab on a South aspect near the ridgline above Maloney Lake. The winds at ridgetop were fairly strong, and were filling it in quickly.

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Avalanche Problem 3: Persistent Slab
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Several persistent weak layers exist in the snowpack, which are mostly graupel and crust combinations. A thin ice layer with large facet formation has been found around 2-4 feet down from the snow surface. A separate layer that formed in early February is still lingering 4 feet below the surface. Varying levels of stability have been observed in these layers across the zone. Typically these layers will be difficult to trigger and have demonstrated increased stability with warmer temperatures and recent rains. However, if you trigger this layer avalanches may propagate significant distances across the slope and could result in avalanches large enough to bury a person. Yesterday, in the headwaters of Lake Fork Creek on a North aspect we were able to get this layer to fail, although hard results ECTP28, there still is energy that can propagate a fracture...you are most likely to trigger this layer in a shallow, rocky, thin spot in the snowpack. 

advisory discussion

 

 

 

recent observations

Yesterday, we toured into Maloney Lake, East of Boulder Lake. Our Test pit at 8,000 feet on a North aspect showed about 1.4  feet of new light density new snow resting on a crust. We were getting moderate results in compression and ended up performing an ECT and got propagation across the block on a crust/facet layer 50cm (1.6 FT) below the surface.  Multiple mit pits revealed that the new snow, again, showed better signs of bonding on Northern, cooler aspects. We were able to get some localized storm slabs to release on some rollovers that were steep and un-supported at the bottom. We observed a couple natural storm slabs that pulled out on the steep North face of Jug Mtn above Louie Lake.

CURRENT CONDITIONS Today's Weather Observations From the Granite Weather Station at 7700 ft.:
0600 temperature: 17 deg. F.
Max. temperature in the last 24 hours: 26 deg. F.
Average wind direction during the last 24 hours: Southwest
Average wind speed during the last 24 hours: 7 mph
Maximum wind gust in the last 24 hours: 15 mph
New snowfall in the last 24 hours: 1 inches
Total snow depth: 65 inches
Disclaimer

This avalanche advisory is provided through a partnership between the Payette National Forest and the Payette Avalanche Center. This advisory covers the West Central Mountains between Hard Butte on the north and Council Mountain on the south. This advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. This advisory expires at midnight on the posted day unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.