Avalanche Forecast
Regions: Snoqualmie Pass.
You’ll want to pay particular attention to the snow as you near the ridge crest or travel onto more exposed features. Take a moment to point out and steer around smooth pillow-like drifts and pockets of snow below fresh cornices where you are most likely to trigger a slab avalanche.
Snowpack Discussion
March 5, 2020 (The regional synopsis is updated every Thursday @ 6 pm)
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Ridgetop wind transport near Washington Pass. 3/4/20 Photo: Josh Hirshberg
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The beginning of March brought the first spring-like weather to the region. The days are getting longer and the sun (when it shines) has a noticeable effect on the snow. Alternating sun breaks and snowstorms is the theme of the week and the avalanche danger fluctuated just as fast as the weather. The southern zones and the east slopes have seen periods of light snowfall and significant sunshine while the northern zones and west slopes have had significant snowfall and occasional sun breaks. Above freezing temperatures were common at lower elevations throughout the region.Â
Last week in review: Temperatures were above freezing at most trailhead locations and concerns about the previous week’s buried surface hoar and weak layers were fading. Saturday temperatures plummeted as strong winds and new snow built wind slabs in most areas and drove the avalanche danger to considerable in almost every zone. Sunday’s calm weather and clearing in most areas helped stabilize wind slabs, but our attention turned to the strength of the sun and daytime warming. Lingering wind slabs and loose wet avalanches were forecast in every zone. For the remainder of the week, the avalanche problems in every zone were confined to the recent snow and each brief storm cycle had us thinking about wind slabs at upper elevations and loose wet avalanches from daytime warming and sunshine.
Spring isn’t actually here -- another round of cold temps and snow showers are on the way this weekend, but this past week’s oscillating weather is a good reminder to begin to shift our mindset. The sun is gaining strength, the days are getting longer, and we begin daylight savings this week. Even a brief period of sunshine can dramatically alter fresh, new snow. Check the mountain weather and avalanche forecasts for the most up to date info, enjoy the backcountry and let us know what you see out there!
--Peter Moore
Wet loose avalanche debris near Snow Lake. 3/5/20 Photo: Dallas Glass
Fresh cornice development from strong winds in the Stevens Pass backcountry. 3/4/20 Photo: Tom Whipple
Avalanche Problems
Wind Slabs
The storm totals for this system don’t look that impressive for the Pass, and we are only expecting 3-4” of snow. This, by itself, shouldn’t really increase the hazard. As a result, you’ll want to look for areas where the wind drifts the snow into slightly thicker and firmer slabs. When you travel near the ridge tops or along features exposed to the wind, look for visual clues to indicate where new small wind slabs may lie. Fresh cornices, drifts behind trees, and smooth pillow-like pockets can help you identify and avoid wind loaded slopes. As the day progresses, you could see more snow falling. This could add to the depth of any wind slab and mask easy to read signs of wind transported snow.
The new snow will accumulate on a variety of old surfaces around the Pass. Reports from the last several days found firm crusts on the surface below 4000’ and on sunny aspects at higher elevations. Cold dry settled snow still existed on shaded slopes at mid and upper elevations. The snow should bond well to the old surface in most areas. Any avalanche concerns are expected to be limited to the upper snowpack above the first major crust you encounter.
Release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..
Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.
Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1