Avalanche Forecast

Sunday morning update

New storm snow avalanche hazards vary across the west slopes of the Cascades and should be the most sensitive this morning. For the Mt. Baker area, be aware of easily triggered storm slabs and stick to lower angled slopes at least initially. In other areas without a slab structure and in terrain not wind effected, watch for small loose dry avalanches near terrain traps like cliff bands where even small avalanches can have big consequences. 

Previous discussion

A strong frontal system will quickly sweep through the Cascades Saturday night and Sunday morning. This system should deliver a nice shot of snow to the west slope of the Cascades with an overall cooling trend continuing on Sunday even as shower activity wanes heading into the afternoon. 

Despite a favorable cooling trend with this storm, westerly winds will build fresh wind slab on lee aspects near and above treeline. Look for wind slab development further downslope than you might expect due to locally strong winds and persistent loading. Watch for firm wind transported or hollow sounding snow. 

Storm slab should be a lesser avalanche concern on Sunday. However, in wind protected areas that experience persistent and intense snowfall rates, locally sensitive storm slab may develop.   

In much of the lower part of the below treeline band there is still insufficient snow for avalanches, so watch for early season travel hazards such as terrain traps, rocks and open creeks. The shallowest snow is at pass level at Stevens, Snoqualmie and White Passes.

Saturday morning update:

Sensitive and widespread soft storm slabs have been reported throughout the terrain near and below treeline in the Mt. Baker area. The slabs were releasing within storm layers and up to 10" deep. Wind transport continued along ridges due to the low density new snowfall. Crystal patrol reported widespread loose dry avalanches running fast on steep terrain, natural and human triggered. Wind effects were relegated to immediately below ridgelines but there was plenty of new snow available for transport.  

Weather and Snowpack

A front crossed the Cascades Friday with 2-8 inches of new snow reported at NWAC stations through early Saturday morning. The new snow was generally on the heavier side and was accompanied by a slight warming trend Friday. Post-frontal showers were generally light on Saturday and ridgetop winds were moderate out of the west. With the mild snow levels seen so far this season, most avalanche problems have been confined to the most recent storm layers found in the upper snowpack.   

Recent Observations

Observations from mid-week indicated a generally stable snowpack.

NWAC pro-observer Simon Trautman was in the Bagley Lakes area near Mt Baker on Friday and at about 5000 feet found dangerous new wind slab conditions due to winds, new snow and the warming trend. He reported a very reactive easy to trigger 15-25 cm new wind slab giving cracking to 2-4 feet and up to 20-30 feet where the new wind slab was deeper. This is a great picture to keep in mind when thinking about the potential wind slab hazard.  

Reactive wind slab in a snowpit on Blueberry Hill in the Mt Baker backcountry on Friday. Photo by Simon Trautman.

The Alpental pro-patrol on Friday reported rain soaking into the snowpack in the below treeline band. They reported a small 2 foot climax avalanche on a rock slab due to the rain and warm temperatures.

Professional observations from the Stevens Pass area (pro-patrol) and Crystal backcountry (Dallas Glass) described generally stable conditions Saturday except for pockets of shallow wind slab found near-treeline. Dallas found shallow wind slab generally just below ridges but observed wind sculpted snow much further downslope.

Mt. Baker pro-patrol reported two climax slides at 3800 ft below treeline that released in steep terrain. These events were likely isolated and related to the extra water content found in the snowpack below treeline.