Avalanche Forecast
Regions: Cascades - East.
You may be able to trigger small loose avalanches in steep terrain. Large cornices hang over many ridges. Expect slightly warming temperatures and sunny skies for Monday.
Discussion
On Sunday, an observer near Holden reported about 1 inch of new snow overnight with loose avalanches in the surface snow and small drifts at upper elevations. Monday will bring a slight rise in temperatures and clear skies.Â
Small drifts formed Wednesday and can still be found near and above treeline. Avalanches will be difficult to trigger in older drifted snow. Large cornices loom on most high ridges from many westerly wind events this winter. Use caution to not travel on or under overhung cornices.
A rain event in early February formed a prominent crust that you can still find near the surface sometimes with an adjacent layer of faceted snow. There are also a couple of layers of buried surface hoar or near-surface facets in the upper 3 ft of the snowpack. It's been a while since any avalanches were reported on these layers but you may still be able to find them, like in this profile from Dirtyface Mountain on March 3rd. Take the time to assess for the snowpack if venturing to higher elevations or more remote and committing terrain.
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
Loose Wet
Expect small loose avalanches near the Cascade Crest. Strong sun will warm sun-exposed slopes and cause wet avalanches where recent snow has slowly accumulated over the past few days. Use caution near terrain traps where these avalanches could be dangerous.
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.
Aspects: East, South East, South, South West, West.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1
Loose Dry
You could trigger loose avalanches on steep shaded slopes and northerly aspects near and above treeline. Triggering avalanches in the surface snow is possible on slopes approaching 40 degrees and steeper. Use extra caution when traveling in very steep slopes near terrain traps such as gullies, rocks, and cliffs. Even small avalanches could injure you if they push you into these features.
About 8 inches of snow incrementally accumulated at upper elevations since Wednesday. Cold temperatures at upper elevations have kept this snow soft and lacking cohesion. Use small test slopes to see if the surface snow slides under your boards or machine.
Release of dry unconsolidated snow. These avalanches typically occur within layers of soft snow near the surface of the snowpack. Loose Dry avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs. Loose Dry avalanches can trigger slab avalanches that break into deeper snow layers.
Loose Dry avalanches are usually relatively harmless to people. They can be hazardous if you are caught and carried into or over a terrain trap (e.g. gully, rocks, dense timber, cliff, crevasse) or down a long slope. Avoid traveling in or above terrain traps when Loose Dry avalanches are likely.
Loose Dry avalanche with the characteristic point initiation and fan shape.
Loose dry avalanches exist throughout the terrain, release at or below the trigger point, and can run in densely-treed areas. Avoid very steep slopes and terrain traps such as cliffs, gullies, or tree wells.
Aspects: North, North East, East, West, North West.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1