Strong outflow winds have formed wind slabs on atypical aspects. Buried weak layers warrant a cautious mindset and terrain use strategy.
Strong outflow winds are drifting the recent snow into fresh wind slabs in a reverse-loading pattern that may be possible to human trigger. These conditions may also bring cornices to their breaking point.
Multiple surface hoar layers have been buried by successive storm events and have shown continued reactivity to human triggering. These layers can be found buried 35-50 cm, 70-120 cm, and 110-160 cm below the surface. These layers have recently produced human triggered avalanches, some of which were remotely-triggered. These weak layers are most problematic at treeline elevations where the surface hoar is well preserved.
Friday night: Clear, strong outflow winds from the northeast, alpine temperature near -22 C.
Saturday: Clear, strong outflow winds from the northeast, alpine high temperature near -12 C, freezing level near 500 m.
Sunday: Clear, light northeast winds, alpine high temperature near -6 C, freezing level rising to 2500 m overnight.
Monday: Clear, light northeast winds, alpine high temperature -1 C, freezing level near 2500 m.
With continuing strong outflow winds, wind slabs are expected to remain to possible to human trigger.
In the aftermath of the storm earlier in the week, avalanches releasing on surface hoar layers have continued. Operators reported several large (size 2-3) avalanches breaking on both the March 9th and March 1st surface hoar layers from human and explosive triggers. Several of these avalanches were remotely-triggered. Check out this MIN from the Shames area for a helpful example.
During intense periods of solar radiation on Thursday, small (size 1-1.5) loose wet avalanches ran on steep, sun-exposed slopes. Cold air may limit solar influence on Saturday, but use caution if the snow moistens.
Two very large (size 2.5-3) natural glide slab avalanches were observed along the Terrace highway on Friday. Maintain conservative margins to avoid areas with glide cracks.
Strong arctic outflow winds are building fresh wind slabs in a reverse-loading pattern. Last week's storm delivered 30-60 cm of new snow to the region with strong southwest winds creating ample snow available for wind transport.
The recent snow is sitting on a weak layer of surface hoar buried 30-60 cm deep in many areas, especially in sheltered areas at treeline and below treeline. See this MIN from the Shames area that shows this layer when it was on the surface. Observers have reported widespread whumpfing and propagation in snowpack tests on this March 9th surface hoar, confirming its propensity for human triggers.
There are several additional layers of surface hoar that are now buried 70-120 cm and 110-160 cm deep that may also be the most prominent around treeline. On south through west facing slopes, this surface hoar may be sitting on a crust, which may increase the potential for triggering avalanches on these layers. Below about 1000m, the recent new snow is sitting on a melt-freeze crust.
A weak layer of facets that formed in January may be found about 150 to 200 cm deep, and an early season melt-freeze crust lingers at the base of the snowpack. These layers have produced a few very large natural and explosive triggered avalanches over the past two weeks.
