Avalanche Forecast
Regions: Snoqualmie Pass.
This recent snow is very light, dry, and unconsolidated. You are most likely to trigger avalanches in areas affected by the wind. Avoid open slopes greater than 35 degrees where you see drifted snow, uneven snow surfaces, or fresh cornices.
Discussion
Snow and Avalanche Discussion
The Snoqualmie Pass area received 12-14†of very light, dry snow Saturday. This new snow fell at very low temperatures and resulted in very low density, blower powder. Normally, with snow totals like this, you’d expect more avalanches. That wasn’t the case, and the forecasted avalanche danger did not materialize. Observations from the Alpental Valley reported a few natural small loose dry avalanches and very shallow soft slabs.
How is this snow going to change tomorrow? And how will that affect the avalanche danger? Tough to say. We’re worried about the recent snow settling. When this happens, the avalanches could become more likely. There are two things ways we could see snow settlement: 1: Time and 2: Sun. Both could be at play on Sunday. This pattern may run contrary to our normal northwest regime, where settlement often means stability. Avalanches may become easier to trigger Sunday. Keep your eye on slopes receiving direct sunshine. Even with these cold temperatures, the sun may create just enough settlement in the snow to create a slab.
Don’t forget, this recent snow is sitting on a weak layer of sugary facets and surface hoar. So far, we haven’t heard of any avalanches on this old snow layer. That may be because the new snow hasn’t formed a slab. Like we just talked about, that could change Sunday. If you see natural slab avalanches, experience sudden collapses, or see long shooting cracks, avoid nearby avalanche terrain.
Snowpack Discussion
New Regional Synopsis Coming Soon
Avalanche Problems
Wind Slabs
The winds on Saturday formed wind slabs on many open slopes including some lower elevation terrain. The winds were generally out of the East and Southeast, which could have created some unusual loading patterns. You’ll want to pay attention to areas where the wind affected the snow surface. Use visual clues such as snow drifts, uneven snow surfaces, and fresh cornices to clue you into locations that could be wind loaded. When you see signs of wind-deposited snow, avoid nearby slopes greater than 35 degrees.
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: Likely
Expected Size: 1 - 1
Loose Dry
With all the recent light, fluffy, unconsolidated snow you may trigger loose dry avalanches in sheltered locations. While these avalanches shouldn’t be big, don’t let them catch you off-guard. Be cautious around slopes where loose dry avalanches can push you off of cliffs, into trees, or bury you deeply in a gully.
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.
Elevations: Treeline, Below Treeline.
Likelihood: Possible
Expected Size: 1 - 1