THIS AVALANCHE ADVISORY EXPIRED ON March 18, 2018 @ 6:15 am
Avalanche Advisory published on March 17, 2018 @ 6:15 am
Issued by George Halcom - Payette Avalanche Center
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Considerable avalanche hazard exists due to recently formed storm slabs that are not bonding well, but resting on slick crusts. Lingering persistent weak layers are buried 1 to 3 feet below the surface mixed into layers of crusts, graupel, and facets. Added snow load today will increase the possibility of Natural avalanches, and make Human triggered avalanches likely. 

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.

 

Avalanche Problem 2: 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 12 to 18 inches from the snow surface. A separate layer that formed in early February is still lingering 3 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. 

advisory discussion

 

 

 

recent observations

Yesterday, we toured multiple aspects near Black Tip and Squaw Meadows and observed a prominent crust under 6-10 inches of new snow. On solar influenced aspects, the new snow had not bonded well and was easily pushed off of the crust with a ski cut, and in mid turn. The upper part of the new snow was very light , and produced minor sluffing on slopes steeper that 35 degrees. Test pits produced moderate compression and easier shear scores, and revealed the slabbier new storm snow to be resting on yet another well preserved graupel layer. Northern aspects stayed a little cooler and the crust did not develop quite as much, and seemed to bond the new snow better overall. The sun came out briefly, but long enough to produce some shallow point releases near steep Southern rock outcrops. 

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.