Avalanche Forecast

A major change is on the way. This storm headed our way will bring along sustained winds and a decent amount of new snow. More snow will fall in areas closer to the crest like at Washington Pass. The temperatures have been quite cold recently, and current snow surfaces are a mix of sun crusts on southerly aspects to weak, faceted snow on northerlies. Recently buried layers were also weak and faceted. The slightly warmer temperatures, and winds with this storm are ideal for slab formation. Now is as good a time as any to remember that most avalanches occur during, or directly after a snowfall event. 

A small wind slab was triggered by a ski cut by a professional guide on a northeast aspect at 7,200ft on Monday. Previously, several dry loose avalanches were reported in steep shaded terrain. A natural wind slab (D1.5) was observed recently in steep terrain below a cliff band on a northeast aspect at 7600ft that entrained quite a bit of loose snow and ran 300ft downslope. Over the past week, the avalanche danger eased, and folks were able to get out and enjoy some very nice days with good stability and great snow in the mountains. This storm may change that for a little while. The old persistent weak layers in the snowpack appear to be rounding and are unreactive in most areas throughout the East-North zone. Be cautious if you venture into areas further east and south of Mazama where you may still find a weaker snowpack structure.

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.