Stevens Pass

Winter-like stormy weather will create dangerous avalanche conditions by Sunday. Wind and Storm Slabs will grow on a variety of terrain features and lee slopes, possibly forming lower on slopes than typical, due to very strong winds. You will be likely to trigger avalanches Sunday so stay well away from avalanche start zones or areas where avalanches could travel to. Use visual clues such as blowing snow, fresh cornices, and cracks in the snow all indicating that you could trigger a Wind Slab avalanche.  Give fresh Cornices a wide margin of safety. 

Heavy rain Saturday morning transitioned to snow by late Saturday afternoon following a strong frontal passage. Very strong winds and further snowfall in moderate showers will continue Saturday night and Sunday.

Continued winter-like stormy weather will create dangerous avalanche conditions by Sunday that will deteriorate further during the day Sunday. 

Wind Slabs will build on lee slopes and a variety of cross loaded terrain features, possibly lower on slopes than typical, due to very strong winds where you could trigger a Slab avalanche. Use visual clues such as blowing snow, fresh Cornices, and cracks in the snow all indicating that you could trigger a Wind Slab avalanche. 

While the bonding of new snow to the old wet snow surface should be favorable, unstable Storm Slabs will build on a variety of steep terrain, especially in those areas receiving the greatest new snow amounts. Watch for deeper stiffened slabs developing Sunday on a variety of aspects.

Fresh Cornices are likely to build along ridges, so give Cornices a wide berth if traveling along ridgelines as they often break back further than expected. Be aware of overhead hazard if traveling on slopes with Cornices above as they may fail naturally or be human-triggered. 

A vigorous storm Saturday caused periods of heavy rain and warm temperatures early Saturday that transitioned to snow or wet heavy snow by Saturday afternoon with shallow new snow beginning to accumulate by Saturday afternoon.  The old rain soaked snowpack has begun to refreeze and form a crust under continued cooling. The Mount Baker and Rainier areas may see more significant snow accumulations at lower elevations than other West Slope areas and Passes zones. New snow has fallen on rain wet surfaces on most slopes.

The April 1st-2nd storm deposited a relatively even blanket of 1.5 feet of snow across the Cascades West and Passes zones and has now been soaked at most elevations. In most locations, last weekend's snow fell on a firm melt-freeze crust (4/1) up to 5,500 ft. 

The newly forming rain crust should form the bed surface for any expected avalanches, however there remain deeper buried layers that continue to be tracked, including:

-A weak layer (3/22) down 2-3 feet (60-90cm) below the snow surface. On sunny aspects, this could show up as a thin layer of firm crust.

-A series of crusts and softer snow about 3 feet below the snow surface.

-The 2/8 crust, now 5-7 feet below the surface. This was associated with the 2/13 facets. Though it's unlikely, if significant water pools on the crust, it could result in very large and dangerous Wet Slabs.

Observations

Central

Several large fresh wet snow avalanches were seen on Lichtenberg Mtn east of Stevens Pass Saturday, following heavy rain in the morning.

NWAC avalanche forecaster Josh Hirshberg was at Stevens Pass Monday and Tuesday. Josh reported 16 to 18 inches (40-45cm) of new snow in sheltered locations. Near ridgeline, winds  transported snow, forming drifts up to 22 inches (55cm) deep. No new avalanches were observed.

NWAC avalanche forecaster Dallas Glass traveled in the Snoqualmie Pass area Tuesday. Dallas found 18-24 inches (45-60cm) of settled storm snow, generally well bonded to the old 4/1 crust. Several natural and human triggered loose dry avalanches were observed. 

South

NWAC professional observer Jeremy Allyn traveled in the Crystal backcountry Monday. Jeremy found wind transported snow above 6000 feet. The new snow was moderately bonded to the old snow surface with the bond strengthening during the day. As the sun came out, sunny aspect quickly became moist to wet and produced rollerballs.