Avalanche Forecast

Following a period of relatively calm and sunny weather, a major storm is moving into the East South region, bringing 6-12” of new snow towards the Cascade crest with lesser amounts further east, creating storm slabs in some areas. Moderate winds gusting strong will create thicker and more reactive slabs near and above treeline, particularly on wind-loaded slopes. Tuesday is a good time to dial back your terrain selection and stick to slopes less than 35 degrees in areas receiving significant (> 6”) snow or wind transport. Avalanche danger is likely to maintain or slightly decrease throughout the day.

Keep in mind that the fresh snow is likely to fall on a variety of weak snow surfaces potentially formed during the recent spate of cool, dry weather. These surfaces may include surface hoar, facets and on southerly aspects, they may lie on a crust. This may contribute to shallow slabs breaking widely and producing avalanches significantly larger and more dangerous than you expect.

In shallower snowpack areas, you are more likely to find and potentially trigger a persistent slab avalanche within the top 1 to 2 feet of the snowpack. A public observation of a human-triggered slab avalanche came from a north aspect at 3200' just north of the Columbia River (Stacker Butte). We don't know what layer the slab avalanche failed on and the report is now several days old, but it's a clear reminder of weaknesses that remain in the upper snowpack. If you find signs of instability such as cracking and collapsing in shallower snowpack areas, dial back your terrain selection to lower-angled and well-supported slopes.

March 10, 2019

February started stormy and cold with very active avalanche conditions on persistent weak layers. The month finished with continued cold temperatures but drier weather allowed avalanche activity to taper off. Persistent weak layers that were buried early in the month (Feb 8th) are now unreactive, though you can still find the grains.

Aside from the series of storms in early to mid-February, most regions have measured relatively light snow accumulation in the past 3 weeks. Snow has stayed soft especially on shaded slopes and faceting and surface hoar have been plentiful. While there has been plenty of sunshine since mid-February, very cold temperatures have kept melt-freeze crust to a minimum on sunny slopes.

A natural loose wet avalanche (D1.5) on a southeast aspect of Lichtenberg Mtn at 5,400ft. 3/10/2019. Photo: Josh Hirshberg

Recent Avalanches

Our attention shifted to the upper snowpack. Recent avalanche problems have largely focussed on wind transported snow and weak snow surfaces on both dry, shaded slopes and sun-exposed aspects. In some locations, a weak layer of surface hoar and facets was buried on March 6th. We’ll keep an eye on this interface as we move into the future.

A skier-triggered storm slab avalanche (D1.5) on Shuksan Arm, north aspect, 5200ft. 03/09/19 Adam U Photo. 

Moving Forward

As we move further into March, there are two points to consider:

• The strength of the March sun: As the sun creeps higher into the sky and the days grow longer, the sun can have a greater impact on the snow surface. When the sun comes out, expect things to change quickly. You may see avalanches conditions change with natural loose avalanches originating from sunny slopes, surface snow becoming thick and heavy, and slabs taking on a moist to wet snow character.

• Weak surfaces: facets and surface hoar have blanketed snow surfaces in many zones. Any significant snowfall will bury well-developed and widespread persistent weak layers. Recently, most storms have not delivered enough precipitation to cause a problem.