Avalanche Forecast

Avalanche danger will increase throughout the day Friday as additional precipitation and warming temperatures impact the area. Expect avalanche problems to grow and become easier to trigger throughout the day. Avoid all slopes greater than 35 degrees Friday as this weather system creates dangerous avalanche conditions.

Moderate to strong winds will form new wind slabs on lee slopes at higher elevations. Use visual clues such as blowing snow, fresh cornices, and snow drifts to identify and avoid steep wind loaded terrain.

Warming air temperatures during the day will create “up-side-down” surface snow conditions where heavier stronger storm snow sits atop lighter weaker storm snow. You will find storm slabs in wind sheltered areas throughout the terrain. Storm slabs are easiest to trigger on convex rollovers, unsupported slopes, and on steeper slopes.

As the day warms and rain begins to fall, storm slab conditions will transition to loose wet snow below treeline. Rain on new snow is an obvious sign unstable snow exists in the terrain. When you see new roller balls, observe fan shaped avalanche debris, or experience rain on snow, limit your exposure to steep overhead terrain where avalanches may initiate.

Other spring time hazards exist in the mountains. Watch for large overhead cornices,  glide cracks and opening creeks.

In general 4-6” (10-15cm) of new snow fell in the area Wednesday night into Thursday. Locally higher amounts were observed. Winds during the snow likely formed soft wind slabs on lee slopes in exposed terrain. This recent snow fell on a new melt-freeze crust formed and buried on 4/11. The thickness and strength of this crust depends on location and elevations.

Below the 4/11 melt-freeze crust the snowpack consist of various melt-freeze crusts, refrozen snow, and strong rounded grains. This has created a strong spring-like snowpack. Avalanches should be limited to the snow above the most recent (4/11) crust layer.

Out of the weak layers that we've tracked through the season, the 2/8 crust can still be identified in many areas 5-7 feet below the surface. This interface 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

NWAC forecaster Dallas Glass traveled in the Stevens Pass area Wednesday. The upper snowpack remained wet allowing for widespread triggered Loose Wet avalanches, beginning small but entraining significant wet snow and becoming large. There was evidence of recent widespread large wet avalanches following the weekends strong storm cycle, however there were many slopes that did not avalanche, holding deep wet snow. 

Stevens Pass DOT and Stevens Pass Pro-patrol reported large and destructive avalanches during control work that released as soft slabs with explosives and quickly entrained wet snow at lower elevations on Monday. In a section of the ski area with minimal skier traffic on the east end of Cowboy Ridge, this explosive triggered slide (SS-AB-D2.5-R3-O) on a north aspect produced 4-5 ft of debris as it entrained old saturated snow below.  

South

NWAC professional observer Jeremy Allyn traveled in the Crystal backcountry Monday 4/9. Through mid-day, Jeremy found poor travel conditions as the surface crust quickly broke down with moist or wet snow in the upper snowpack.  Recent large Wet Loose and one Wind Slab avalanche from the weekend were observed in surrounding terrain.