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RegisterMar 10th, 2019–Mar 11th, 2019
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You may still find and trigger a slab avalanche in isolated areas where recent storm snow has consolidated and sits upon recently buried weaker snow. Loose avalanches, particularly loose wet avalanches, may release naturally or be human triggered as the sun comes out Monday. Take care around terrain traps that would amplify the consequences of a small avalanche.
While loose avalanches were the most common avalanche seen or triggered over the weekend, a few small natural and skier triggered slab avalanches were reported in the Crystal backcountry (Pickhandle Point/Crown Point area) on Friday and Saturday covering a variety of aspects.
The 3/6 weak layer (buried surface hoar) was identified in at least one avalanche crown. This weak layer was identified and reactive in some test pits in the Paradise and Crystal areas 8-14 inches from the surface. A NWAC forecaster traveling above treeline on Mt. St. Helens Saturday reported large whumpfs on a SE aspect at 7600'. Facets over a sun crust showed strong over weak snow 14" from the surface. The lingering storm slab problem is likely confined to isolated areas near and above treeline as the recent storm snow on shaded aspects is still uncohesive (loose) in most areas.
It's been several weeks since avalanches released down to the early February crust. After more observations targeting this interface several feet down on Saturday, we feel we have enough information to drop deep persistent slab from the avalanche problem set. We'll continue to monitor this interface as we get deeper into the spring and weather patterns change.
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.