Avalanche Forecast
Regions: Snoqualmie Pass.
Expect increasing clouds, warming temperatures, and wind at upper elevations. You can trigger loose avalanches on steep slopes (both sunny and shaded) where you find soft, weak snow on the surface. Don't linger on steep sunny slopes as temperatures warm and use caution near cliffs and gullies, where small avalanches could be dangerous.
Discussion
Snow and Avalanche Discussion:
On Friday through Sunday, observers reported loose avalanches on both shaded and sun-exposed slopes in the Alpental Valley, the Commonwealth, and Middle Fork of the Snoqualmie drainages. On Thursday and Friday, observers reported triggered and natural shallow and soft slabs on leeward, wind-loaded (north through east) slopes near and above treeline. On Thursday observers easily triggered small slabs on southerly slopes where the recent snow rested on a crust.Â
Up to 8 inches of snow accumulated between Wednesday and Friday morning with drifted snow forming soft slabs up to up to 1-foot deep. The recent snow buried a variety of old surfaces including crusts, firm wind-packed snow, facets, and surface hoar. Keep this interface on your mind, and use quick tests to evaluate it as you move through the mountains.
A natural slab avalanche (D1) on a northeast aspect of Chair Peak at 5,200ft. 3/10/2019. Photo: Dallas Glass.
Snowpack Discussion
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.Â
Moving Forward
As we move further into March, there are two points to consider:
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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.
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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.
Avalanche Problems
Loose Wet
There may be enough sun and the warm temperatures for isolated loose wet avalanches on steep sunny slopes. They may even run naturally. These avalanches will be small and easy to predict. Building clouds should put an end to these avalanches for the latter half of the day. Don't linger on or under steep, sun-exposed slopes. Rollerballs and soft, moist snow surfaces are signs that loose wet conditions are building.
If you're traveling on slopes 40 degrees and steeper, you could also trigger fast-running loose dry avalanches on shaded aspects. The recent snow buried a variety of old snow which made for slick bed surfaces for any triggered avalanche. Keep this interface on your mind, and use quick tests to evaluate it as you move through the mountains.
Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.
Several loose wet avalanches, and lots of pinwheels and roller balls.
Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.
Elevations: Treeline, Below Treeline.
Likelihood: Possible
Expected Size: 1 - 1