Avalanche Forecast

Light snow showers and decreasing westerly winds are expected on Wednesday

Expect small to find small to large wind slabs in all elevation bands, but particularly near and above treeline. These formed during the recent strong frontal passage on Monday. With generally minimal additional new snow and wind loading, wind slabs should begin to stabilize slightly. Depending on the location these wind slabs may still be touchy or trending toward unreactive. With limited recent observations on much of the terrain, uncertainty is high, approach ridge-lines via safer, low-angle routes on Wednesday and watch for wind-stiffened or chalky snow.

Storm slab has been removed as a problem in this zone due to a generally right-side-up snowpack.

Small loose dry avalanches are possible in steeper terrain. Avoid steep slopes where the consequence of an avalanche may be significant.

A warm and moist system Suunday through Monday night brought higher density snowfall to mid-to-upper elevation sites on the east slopes of the Cascades, with the heaviest snowfall occurring in the Cascade East-North zone on Monday afternoon. The snow came in with a cooling trend and decreasing density, forming right-side-up surface snow. The snow bonded well to the old snow interface in the north (where rain did not extend into skiable terrain during the recent storm cycle) and is assumed to be well bonded to any rain crusts or old snow interfaces in the central and south. A cool and unstable air mass continued to add low-density snow, particularly closer to the Cascade crest. Near Washington Pass, 18" of snow accumulated from Sunday-Tuesday. Lesser amounts can be expected in the central and south. Mission Ridge only picked up 1-2".

Winds have re-distributed the storm snow into slabs of varying reactivity with highly reactive wind slabs reported in the shallow slabs developing under intense winds at Mission Ridge. Terrain near ridgelines in other areas has not been observed recently.

Estimated recent snow totals at mid-elevation sites; 15-25" in the northeast zone through Monday afternoon with 5-15" in the central-east and southeast Cascades.

The weight of the recent snow is causing relatively rapid settlement  (7" in 24 hours at Lyman Lake Monday) of the underlying lower density snow which has accumulated since the 1/16 crust.

Winds throughout the active period since 1/16 have been redistributing snow, but the strongest winds were in the Central Cascades, especially Mission Ridge.

Some recent observations from around the east slopes central/north zones found buried surface hoar above the 1/16 crust. There is still quite a bit of uncertainty about the distribution of this layer in these zones. Extra caution should be taken when traveling in areas further east of the crest or in areas where less snow has been received. Snow profiles and snowpack tests are the only means to identify and locate this layer. A non-exhaustive list of locations where surface has been found on the 1/16 crust includes specific slopes in Icicle Creek and the Twisp R., and in isolated locations near the Barron Yurt and in the bottom of Liberty Bowl. Reactivity on a melt-freeze crust 20 cm below the surface has also been observed at Mission Ridge.

Observations

North

On Tuesday, NCMG was in the Washington Pass area in the 4000-7000 ft range and observed a recent cycle (from Monday or Monday night) of of generally cornice-fall triggered slab avalanches up to size D2.5 (large to very large). The recent storm snow was well-bonded to the older snow, but winds had re-distributed the snow negatively affecting ski quality. Wind slabs near and above treeline were isolated and stubborn. Storm slab was a non-issue in the terrain traveled. They found the 1/16 crust down 150 cm and very deep snowpack with a total snow depth of 340 cm.

On Sunday, NCMG in the Washington Pass area found the 1/16 crust about 3+ft (1 m) down on non-solar aspects. New storm snow was becoming heavier throughout the day. One natural wind slab was observed in steep terrain. 

On Friday, North Cascades Mountain Guides found the upper snowpack generally gaining strength. Some snowpack test failed below the 1/16 crust.

Central

On Tuesday, Mission Ridge Pro Patrol reported results from test pits at 6400 ft on a north aspect, where strong 70 mph winds had formed shallow, but very reactive layer of wind-packed and wind-transported snow over lower density older storm snow. They also found a reactive layer of 1-2 mm melt freeze crust down 20" (ECTP23) and a reactive layer of surface hoar on the thick December 15th melt freeze crust (ECTP27). The total snow depth was 200 cm in this wind-loaded location.

On Sunday, NCMG was on Dirtyface Mountain and reported a deep and very upside-down upper snowpack that was not showing the anticipated reactivity given the structure. Buried wind slabs were present, but unreactive near ridge crest.

Mission Ridge Ski Patrol reported very high winds and active wind loading on N-NE slopes Saturday with very reactive wind slabs producing 4-30" crowns. In wind sheltered locations, soft surface snow was found. Surface hoar had previously been observed in the area on the 1/16 crust.

A public observation from Wednesday in the Blewett Pass area identified basal facets at the bottom of the snowpack and surface hoar above the most recent crust. Snow cover was still regionally low in this area.

South

No recent observations