Southwest wind and an additional eight to ten inches of new snow in the past 24 hours loaded avalanche start zones near ridgelines. This recent loading combined with the previous three days snowfall has added stress to weak layers of snow which sit near the base of the snowpack. The remotely triggered and destructive hard slab avalanche which occurred yesterday afternoon on the west side of the Tetons indicates the potential for very large avalanches to occur. This avalanche was triggered from low angled terrain near a steep, wind-loaded ridgeline at around 9,600’. Widespread reports of collapses in the snowpack in middle elevations serves as a reminder that this persistent slab remains a potential problem there as well. Today is a good day to travel conservatively and allow the buried weak layers time to adjust to recent loading. Avalanche danger is Considerable today at upper elevations where wind slab and persistent slab human-triggered avalanches are possible. Middle elevations have similar avalanche concerns though shallower and fewer wind slabs keep the danger level at Moderate. Carefully evaluate the terrain where you plan to ski or ride or better yet, stick to lower angled slopes where these slabs don’t exist. Lower elevations have less snow coverage and lack the weak layers of snow. Low avalanche danger exists there.
Strong wind during the past four days has drifted snow onto wind sheltered slopes. Signs of wind loading include cornices, wind textured surfaces and stiffer surface snow underfoot. These slabs can crack and fail easily as a thin slabs up to three feet thick or might break on more deeply buried weak layers and become much more destructive and unmanageable.
Weak snow that formed during a prolonged dry period and was buried on December 5th remains a layer of concern in terrain above 8500 feet. This avalanche type could be triggered from a connected slope near a steeper slope or from below. A very large avalanche could occur on this problem layer especially where a thick slabs lays on top. A slab avlanche with a crown up to ten feet thick was reported yesterday afternoon on a wind loaded slope west of the Tetons.
Arctic air will remain in place tonight and into tomorrow. Expect mountain lows tonight between -10 and -15 and rising to the negative single digits tomorrow. Ridge top winds will be in the 10-15 mph range with a trace to an inch of snow falling overnight and another inch or two falling late in the day tomorrow.As recent wind slabs and storm snow settles and bonds, the risk of natural avalanches continues to decline. Unfortunately, the recent loading increased the strain on the weak layer associated with the Dec 5 crust. This persistent slab remains a real concern. Where our two avalanche problem types converge is where you could trigger the largest avalanche with slab thicknesses five or more feet thick in the Tetons and possibly Grey’s River area, with smaller slabs up to 3 feet possible at Togwotee. Steep slopes and areas above 8,500’ where this layer is especially weak or overloaded will continue to hold the potential for these large avalanches that will be easily capable of burying a person. The avalanche danger will be Moderate at middle and upper elevations of all zones tomorrow but you will need to evaluate the snowpack and terrain carefully before committing to a slope.
