Avalanche Forecast

Expect widespread avalanches in the new snow including many natural avalanches. Many of these could be big enough to kill you. The most dangerous areas will be steep slopes where new snow and wind have deposited 2 feet or more of cohesive snow since Friday. Select appropriate terrain to stay safe. Stay out of open slopes steeper than 35 degrees. Be aware of areas where avalanches commonly run. Avoid traveling below avalanche terrain and stay out of large avalanche paths. Only go into the backcountry today if you are sure of your ability to avoid avalanche terrain.

With several overlapping avalanche problems this will be a challenging time to travel in the mountains. While Storm and Wind Slabs exist in the upper snowpack, very dangerous Deep Slabs lurk below. It’s possible that avalanches in the upper snowpack could step down to deeper layers, triggering a very large and destructive avalanche. Deep Slab avalanches are very difficult to predict and give little warning sign. While they may be difficult to trigger your chances of surviving one are slim. If you dig 2-3 feet below the snow surface, you will find a thin layer of sugar-like facets adjacent to a hard crust. You can dig snowpits and use snowpack tests to confirm the strong over weak snow layers of the Deep Slab avalanche problem. 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.

Heavy snowfall and strong winds have elevated avalanche danger, once again. Up to 1.5 feet of snow accumulated across the West Slopes by Saturday evening. Another 1-2 feet of snow will fall with strong winds by late Sunday. Snowfall starting at the end of the work week fell on a variety of surfaces including old snowflakes, surface hoar, and possibly some small facets.

Widespread natural avalanches were reported from the Mt Baker and Snoqualmie pass areas on Saturday. These were soft slab avalanches and some loose avalanches in the recent snow 1-1.5 feet deep with a few reported as big enough to bury a person. Some of these avalanches ran within the new snow while other slid on the interfce of new and old snow. Observers have not consistently found problematic weak layers at the February 23rd interface.

Last weekend, observers reported a widespread cycle of large to very large avalanches occurring with a potent storm. Avalanches ran in the 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. 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 results from the Stevens and Snoqualmie pass areas. In the Mount Baker area the weak layer is more intermittent and 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 and Snoqualmie Pass

On Saturday, Alpental Patrol reported that slab avalanches were easily triggered in the recent snow with ski cuts during control work. An NWAC observer reported many similar natural avalanches in the adjacent backountry at Snoqualmie Pass.

Also on Saturday, NWAC staff reported two different locations near Snoqualmie pass. While the 2/13 facet layer is showing rounding, test results indicated that the potential for triggering an avalanche still exists. This supports numerous similar snowpack tests results Stevens and Snoqualmie passes, the Crystal and Mt Rainier backcountry and to some extent the Mt Baker backcountry all conducted over the last week.

On Tuesday NWAC staff traveled through popular backcountry terrain near the Skyline area of Stevens Pass, finding the 2/13 facets on most slopes.

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.

South

On Friday NPS rangers in the Paradise area reported 3-4 feet of snow over weak facets. No wind transported snow was observed.

NWAC Forecaster Dallas Glass observed a large audible whumph caused by a collapsing weak layer Tuesday near Paradise. Snowpack tests in the area indicated the persistent weak layer could fail and produce avalanches up to 4 feet deep.

No recent observations have been received from the Crystal backcountry. A higher level of uncertainty exists in this area.