Avalanche Forecast

Increasing clouds from south to north on Thursday will limit solar radiation on Thursday with very light mixed precipitation arriving in the south part of the Cascades Thursday evening. An inversion continues and lower slopes will have cooler temperatures and isolated low clouds. 

Lingering wind slabs should be less sensitive to triggering on Thursday and confined to near and above treeline terrain. However, Wednesday's observation from Rock Mountain in the nearby Stevens Pass zone suggests the wind slabs may continue to be reactive in some locations, so continue to exercise caution. Continue to watch for areas of recently wind transported snow such as fresh cornices, snow drifts, and uneven snow surfaces. Identify and avoid locations where recent wind loading occurred.

Wind slabs can be deceptively difficult to manage in the terrain. Take a moment and read our recent blog post by NWAC Pro Observer Jeremy Allyn on wind slabs.

In many areas, firm surface crusts will make for difficult travel conditions so be prepared to self-arrest and think about the sliding hazard before crossing steep slopes.  

In the Mission/Blewett area, be aware of the low likelihood of triggering a persistent slab in isolated areas on non-solar aspects above 5000'. Varied surface roughness combined with an overall shallow snowpack made for a low likelihood of finding the right terrain to support a persistent slab avalanche. However, you can dig snowpits to confirm the existence of basal facets well before entering avalanche terrain and adjust your travel to respect this low likelihood/higher consequence problem.

Despite all this new snow, early season hazards still exist. Many creek beds have still not filled in for the winter.

Cool weather east of the Cascades has slowed the stabilization of wind slabs formed during the recent active weather pattern. However, on Monday and to a lesser extent on Tuesday and Wednesday, warmer air worked it's way aloft, with higher elevation stations such as Lyman Lake, Mission Ridge and Dirty Face warming near or above freezing while lower elevations stayed in the freezer (see graph below).

Winds toward the end of the last storm cycle in late December formed firm and initially reactive wind slabs on a variety of aspects.

Storm totals from across the east slopes of the Cascades show 1 to 2 feet of snow (highest storm totals Lake Wentachee and Holden area) fell during the series of storms ending Saturday Dec. 30th. 

Snowdepth decreases substantially the further east of the Cascade crest one travels. In many areas below treeline, there is not enough snow to present an avalanche danger. 

Observations

North

North Cascades Mountain Guides were in the Washington Pass area again on Tuesday. They found steep southerly and westerly aspects getting significant solar radiation effect above 5,000 feet with surfaces a mix of moist and melt/freeze depending on timing. They also found up to 1 cm surface hoar in avalanche terrain below the inversion layer (up to 5,400 ft).

North Cascade Mountain Guides were in the Washington Pass area Friday through Sunday. By Sunday, sensitive storm slab layers were gaining strength and becoming unlikely to trigger.  Wind slabs were thought to be stubborn but were still avoided or approached cautiously above treeline. One natural cornice release was observed on Sunday. 

Central

A NWAC forecaster was in the Diamond Head area of Blewett Pass on Tuesday and traveled on non-solar aspects up to 5800 feet. 2-3 mm basal facets were rounding but present above 5000' on NW-N-E aspects. Large column tests showed the 2 ft (60 cm) slab above this layer was reactive and likely to propagate. However, varied surface roughness combined with an overall shallow snowpack made for a low likelihood of finding the right terrain to support an avalanche. Just like the nearby Mission Ridge area, this layer will need to be watched moving forward.  Other pertinent observations from the area include a rain crust observed up to 5400 feet. Snowdepths were quite low in this area, making backcountry travel difficult at lower elevations, wind scoured areas and on solar aspects. 

Mission Ridge Pro Patrol reported very sensitive wind slabs observed around the area Saturday. A natural avalanche cycle was observed from Friday night. Avalanche control work within the ski area Saturday produces 1-4 ft wind slab avalanches. The larger avalanches released to ground on 1 mm basal facets.

South

No recent observations