Avalanche Forecast

A strengthening surface crust will limit the avalanche danger Wednesday. Shallow new snow may be transported near ridges, especially near and above treeline, where small wind slabs may be possible to trigger on steep lee slopes. Avoid steep open slopes showing signs of recent wind loading.

Several older deeper persistent weak layers exist in the snowpack. This is a low likelihood-high consequence scenario. These difficult to trigger avalanches may need a large trigger or from a thinner spot on the slab. While it may be very difficult to trigger these deeper layers, any avalanche failing on them will be large and destructive. The avalanche that resulted in a fatality Saturday on Park Butte near Mt. Baker is believed to have released on the 2/8 crust - 2/13 facet interface. This is a recent example of the low likelihood-high consequence structure that remains in our snowpack.

Persistent slab problems in the upper snowpack have recently been reported in the Steven Pass area and the East Slopes of the Cascades. Without any recent avalanche activity or snowpack observations confirming their presence for the other West Slope Zones, we are removing the Persistent Slab problem moving forward. 

Limit your exposure to overhead cornices as you travel. They may fail without warning due to daytime heating and the sun.

Sunshine and temperatures in the 40's to 50's over the past few days has allowed for significant snowpack settlement and for a variety of surface conditions to develop. Several melt-freeze cycles over the past few days has allowed for a strengthening snowpack. Steep shaded north facing slopes are hanging on to some settled old snow that fell Thursday.

Clear weather over the past few nights has allowed for surface hoar or near surface faceted snow to develop on many slopes. These surfaces are easily destroyed by wind or sun and warming, so may end up being widely variable when future snowfall occurs. Precipitation falling Tuesday afternoon has begun as rain in most areas and hopefully destroyed much of these surface crystals.

Several natural slab avalanches were reported Monday around the Mt Baker area, including Shuksan. These slab avalanches released from starting zones above treeline on SW-W-N aspects.  A snowmobile rider triggered a fatal deep persistent slab avalanche Saturday in the Mt. Baker backcountry.  

Previous storm snow fell across the western regions of the Cascades Thursday night and Friday. Significant changes in snow totals were experienced with elevation. Wet heavy snow and rain was observed in up to 5500’ at Crystal, 4400’ at Snoqualmie, and 4300’ farther north. Above these elevations, 12-20 inches of new storm snow accumulated. During the last few days of warm weather, the snowpack has settled back to similar depths before Thursday's storm.  

Generally SW winds transported the snow in all regions forming wind slabs on lee slopes and cross-loaded mid-slope features. These wind slabs have mostly settled and stabilized over the past few days of warm weather. However, natural slab releases have been reported both Monday and again Tuesday in the Mt Baker area on previous wind loaded slopes, indicating the wind slab problem persists.

The recent snow fell on a variety of old snow surfaces including settled cold snow and new melt-freeze crusts. There is potential in some locations that surface hoar and/or near surface facets were buried.

Several older persistent weak layers exist within the snowpack. On E-S-W aspects a thin facet-crust combo has not been widely found or reactive in quite some time. An older, deeper and more widespread persistent weak layer has been observed for several weeks. Weak sugary facets (2/13) sit just above a firm crust formed and buried in early February (2/8). This crust is generally found about 3-4 feet below the snow surface.

There are no other significant layers of concern below the 2/8 crust.

Observations

Baker

On Tuesday, pro patrol at Mt Baker reported a natural slab release on Table Mountain. North aspect about 5000 ft estimated 1.5-2 ft X 150 ft. It was unclear if a cornice failure was the trigger or just the warm temperatures in the 40's.  

Pro patrol at Mt Baker reported seeing several large natural slab avalanches releasing Monday above treeline on a variety of aspects ranging from SW-W-N, likely a result of the very warm temperatures. On Tuesday 

On Sunday, NWAC professionals near the Park Butte accident site observed widespread wet loose avalanche activity on steep solar aspects, including a long running wet loose in the Sisters Range that became very large (D3). In this area on a NE aspect at 5200', the 2/8 crust is down 4 ft (1.2 m) with a layer of facets above the crust. Recent wind effect was noted throughout the immediate terrain. 

Snoqualmie

Backcountry skiers triggered and were caught in a wind slab avalanche on a NW aspect just below the summit of Humpback Mountain Saturday. They were not buried or injured but did lose some gear. Generally small wet loose avalanches were reported by Snoqualmie DOT Saturday on steep solar slopes. 

An avalanche professional at Alpental reported rain up to 4400 feet Thursday night. Two new natural wind slabs were observed in steep NE facing terrain.

South

NWAC professional observer Jeremy Allyn traveled in the Crystal Backcountry Monday, finding older wind slabs to have stabilized. Easterly winds were keeping surfaces cool and limited wet snow avalanches. No wet snow avalanches were seen Monday, despite the warm temperatures. 

On Saturday, Crystal Mt Ski Patrol reported two new natural avalanches on NW slopes around 6000'. These D1.5 avalanches occurred mid-day. They also reported large natural slab avalanches on NE aspects on the Cowlitz-Chimneys across from the ski area in Mt. Rainier National Park. These avalanches likely occurred Saturday afternoon with this photo taken on Sunday by Peter Dale.  

NWAC professional observer Jeremy Allyn traveled in the Crystal Backcountry Friday. He found significant wind transportation of the new snow above 6000’. A cornice failure triggered a widely propagating wind slab 2 feet deep on an E aspect of East Peak. Observations generally demonstrated the new snow was bonding well to the old snow surface.

Also Friday, Crystal Mountain ski patrol reported several new large crowns seen across the White River valley in the Sourdough Mountains. Avalanches occurred on NE aspects and were estimated to be 4-5 feet deep. Wind transported snow was observed on the upper mountain.