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RegisterFeb 25th, 2018–Feb 26th, 2018
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Fresh Wind Slabs and lurking Deep Slabs have combined to create dangerous avalanche conditions. After the latest round of heavy snow and intense wind, you can trigger large and dangerous avalanches. Stay safe by avoiding slopes steeper than 35 degrees, obviously wind loaded features, and staying out from under large open slopes.
Triggering large avalanches is still likely. Many of these could be big enough to kill you and even very large and destructive. The most dangerous areas will be steep slopes where new snow and wind have deposited 2 feet or more of cohesive snow since Friday. Use conservative decision-making and terrain choices. Avoid obvious drifts and deep pillows of wind deposited snow. Minimize your exposure to areas where avalanches commonly run by staying away from open slopes steeper than 35 degrees and out from under large avalanche paths.
With several overlapping avalanche problems this is a challenging time to travel in the mountains. Storm and Wind Slabs eixst in the upper snowpack and very dangerous Deep Slabs lurk below. An avalanche triggered in the upper snowpack could step down to deeper layers, resulting in a very large and destructive slide. While Deep Slab avalanches may be difficult to trigger your chances of surviving one are slim. Your best way to stay safe from these avalanches is to avoid triggering avalanches in the upper snowpack. Excellent travel conditions can still be found on slopes less than 30 degrees that are not connected to steep overhead slopes.
We’re on the tail end of a major avalanche cycle. Observers reported widespread avalanches throughout the West Slopes over the weekend. One person was killed in an avalanche south of Snoqualmie Pass on Sunday. Our condolences go to the friends and family of the victim. If conditions allow, NWAC staff will visit the accident site. A very large natural avalanche crossed Highway 20 east of Newhalem on Sunday.
A break in the weather is allowing avalanche conditions to ease. Triggering avalanches remains likely Monday. Heavy snowfall and strong winds elevated avalanche danger over the weekend. 2-3 feet of snow accumulated across the West Slopes since Friday. This fell on a variety of surfaces including old snowflakes, surface hoar, and possibly some small facets. Observers have reported inconsistent buried weak layers at the February 23rd interface.
Over a week ago, observers reported a widespread cycle of large to very large avalanches ran with a potent storm snow as well as on facets, buried on the 13th of February. In many locations these weak sugar-like facets sit 3 feet below the surface on or adjacent to a hard crust layer. If you dig that far into the snowpack, you will find a thin layer of sugar-like facets adjacent to a hard crust. You can use snowpits and snowpack tests to confirm the strong over weak snow layers of the Deep Slab avalanche problem. Avalanches, collapses, and whumphs have been triggered on this persistent weak layer well after last weekend’s initial avalanche cycle.
Snowpack test and observations from around the region continue to demonstrate that this layer can fail and produce avalanches. Tests and profiles show the most consistent indication for triggering Deep Slabs at Paradise on Mt Rainier and Stevens and Snoqualmie pass areas. Observers are now reporting a wider range of test results and observations on the 2/13 facets, including some indication of that this weak layer is slowly improving. In the Mount Baker and Crystal area the problematic weak layer is more intermittent. At Mount Baker it can often show up as facets around a series of crusts.
A thin rain crust formed and was buried on 2/17 near and below 4000’ in the Snoqualmie area. Limited information about this snowpack layer has been reported other than it is ski-supportable.
Below the 2/8 crust there are no significant layers of concern.
Observations
Stevens Pass
On Sunday, Stevens Ski Patrol reported reactive conditions, triggering avalanches up to 3 feet deep in the recent storm snow with control work. NWAC staff observed Wind Slabs forming in open areas below treeline. They also reported tests indicating skier triggering on the 2/13 facets 90cm below the surface.
The most recent Persistent Slab avalanche was triggered on Monday at Stevens Pass backcountry (Stevens Pass-Hollywood Bowl-2-19). It failed on facets just above the 2/5 crust.
Snoqualmie Pass
On Saturday and Sunday, NWAC staff reported multiple locations near Snoqualmie pass that while the 2/13 facet layer is showing rounding, test results indicated that the potential for triggering an avalanche still exists. On Saturday, NWAC observers and Alpental Patrol reported numerous soft slab avalanches in the recent snow.
South
On Sunday, NWAC observer, Jeremy Allen reported blizzard conditions, small triggered slab avalanches in the new snow, and signs of rounding and variable test results on the 2/13 facets.
On Friday NPS rangers in the Paradise area reported 3-4 feet of snow over weak facets.
NWAC Forecaster Dallas Glass observed a large audible whumph caused by a collapsing weak layer last week near Paradise. Snowpack tests in the area indicated the persistent weak layer could fail and produce avalanches up to 4 feet deep.
