Avalanche Forecast

The recent storm buried a mix of sun crusts on southerly aspects and weak, faceted snow on northerlies. Only a couple inches of snow was recorded at the Washington Pass weather station, but more snow was observed just west of there. The big story, however, is what did the winds do to the upper elevations? A decent amount of low density, cold snow was available for transport prior to Monday. The winds increased during the day and into Tuesday likely building reactive wind slabs at the higher and more exposed areas. Small wind slabs were still reactive on Sunday, where a skier triggered a D1 wind slab on a northeast aspect at 7,200ft. That occurred before this system blew through.

Where firm wind slabs overlie weak, faceted snow, these may act in suprising ways, cracking quite wide over the terrain. The sun should make an appearance on Wednesday, and with it, a rapid change in snow surface conditions. Loose wet avalanches may run on steep, south facing slopes in areas that did pick up over a couple inches of new snow. 

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.