Avalanche Forecast

The avalanche danger Tuesday will continue to gradually decrease with cool temperatures and generally light snow showers expected.

You could still trigger an avalanche Tuesday, but avalanches are becoming more difficult to trigger as the extensive storm and wind slabs deposited last weekend gradually settle and stabilize. Continue to watch for areas that received significant wind loaded snow, such as leeward slopes below ridges. You may also find them in unique areas like cross-loaded terrain features mid-slope and in open areas below treeline. Avoid steep slopes where the wind deposited thick pillows of snow or obvious wind features. 

The new snow has added to the Persistent Slab avalanche problem. Slopes that previously lacked cohesive snow over the facets, may now have developed slabs. Weak sugary facets can be found 2-3 feet below the snow surface and above a firm crust. This is the perfect depth for human triggered avalanches. Two skier triggered Persistent Slabs have occurred last week in the Washington Pass area. It may now be easier for you to trigger these avalanches than prior to this storm. Continue to stay off of large open slopes where you could trigger a Persistent Slab avalanche. Collapsing and cracking are obvious signs that you could trigger a Persistent Slab. Use extra caution if you observe these signs of instability. 

The avalanche danger has improved markedly as we move beyond the dangerous avalanche conditions that developed Sunday and unfortunately claimed 3 lives in two separate accidents near Snoqualmie Pass. NWAC field staff traveled to both accident sites to investigate the avalanches in preparation for forthcoming accident reports. Our condolences go to the friends and families of the victims. 

A very large natural avalanche crossed Highway 20 east of Newhalem on Sunday.

Up to 1.5 feet of snow fell with strong wind across the East Slopes on Sunday. Winds Slabs capped the existing snowpack on leeward slopes. Small isolated wind slab also formed Thursday and Friday. Prior to this storm about 1 to 2 feet of generally soft snow has been reported over an old (2/5) crust from early February. Weak sugary facets can be found above this crust in some locations. This persistent weak layer has failed in two reported skier triggered avalanches over the last week.

While several layers exist in the snowpack, there are no significant layers of concern below the 2/5 crust.

Observations

North

On Monday, the crown of a large avalanche was visible on Scaffold Ridge (Twisp River) in the North Cascades. Interestingly the red line in the photo marked the initial crown width that released Sunday and the remainder of the slab released sometime later Monday morning.

Large natural slab avalanche visible on Scaffold Ridge in the North Cascades, starting zone about 7300'. Image, Matt Firth  

Avalanche professionals in the Washington Pass area Thursday through Saturday reported several small skier triggered wind slabs. Collapsing was reported on Saturday.

The most recent persistent slab avalanche occurred on Wednesday near Harts Pass. The avalanche was about two feet deep and 90 feet wide. It occurred on a NE aspect at 6000’.

Central

Mission Ridge Ski Patrol Reported many small natural avalanches in wind drifted areas on Sunday.

Observers reported triggering small avalanches on Blewett Pass and in the Wenatchee Mountains over the weekend.

NWAC field staff traveled in the Icicle Creek area Wednesday on NE facing slopes up to about 6000 feet. The persistent layer we are tracking was found consistently buried about 2 ft from the surface, though the distribution of this layer was intermittent. In many areas the snow above the facet/crust layer was low cohesion powder, lacking the ability to propagate a slab avalanche. Shallow fresh wind slabs were noted near and above treeline.