Avalanche Forecast

Continued warm temperatures and sunny weather will maintain dangerous avalanche conditions Monday.  

You will be able to trigger wet snow avalanches Monday as warm temperatures and sunny skies create wet snow conditions. However, E-SE winds will locally cool the snow surface in the central and south Cascades, creating a more variable loose wet problem than Sunday. Expect new rollerballs, pinwheels, and loose wet avalanches to occur. These conditions will develop first on steep rocky slopes receiving direct sunshine and especially on wind sheltered slopes. Unstable wet snow will spread to other aspects as the day warms. As water reaches deeper weak layers in the snowpack, wet slab avalanches may occur. If you see any evidence of new wet slab avalanches dial back your terrain use and avoid all avalanche terrain.

You are most likely to find and trigger lingering wind slab avalanches on shaded slopes where winds recently deposited snow. Use visual clues to identify and avoid slopes where wind loading has occurred.

Several older deeper persistent weak layers exist in the snowpack. This is a classic low likelihood-high consequence scenario. Just because you see tracks on a slope does not mean it is safe. 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 down to 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.

Mild temperatures and sunny skies effected snow surfaces Saturday and Sunday. Widespread wet loose activity was reported Sunday across the west slopes of the Cascades on steep sunny slopes. Several natural slab avalanches were reported in the Crystal, adjoining Mt. Rainier and Snoqualmie Pass backcountry Saturday. A snowmobile rider triggered a fatal deep persistent slab avalanche Saturday in the Mt. Baker backcountry.  

New 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.

Generally SW winds transported the snow in all regions forming new wind slabs on lee slopes and cross-loaded mid-slope features.

This new snow has fallen 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 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. 

Mt Baker ski patrol reported widespread wet loose activity on solar aspects (E-W) up to size 1.5 Sunday afternoon. A snowpit on a NNE aspect at 5200' Sunday showed recent storm snow well settled and generally right-side up in the upper snowpack. 

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

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.