Avalanche Forecast
Regions: Cascades - North East.
The new snow buried variable and weak old snow surfaces. Widespread natural and human-triggered avalanches were reported recently. Continue to use extra caution around steep slopes at upper elevations, and put plenty of space between where you travel and large pieces of terrain where avalanches could start or run to from overhead slopes.
Discussion
Snow and Avalanche Discussion
The Washington Pass area received over 1ft of new snow (1.25in SWE) since Monday. On Wednesday, we received reports of a widespread natural storm slab avalanche cycle at all elevations and aspects. Avalanches with the widest propagation occurred on southerly slopes. On Tuesday, a remotely triggered avalanche occurred on the old/new snow interface where buried facets on a crust were found (observation). Shooting cracks and touchy slab conditions at ridge crest were also reported. The old snow surface is weak, and all observations point to dangerous avalanche conditions in the northeast Cascades right now.
Most avalanche accidents occur with Considerable Danger. Continue to be aware of your surroundings and check for instabilities. Ask yourself, "Am I in avalanche terrain? Could the snow slide?" Traveling one at a time is good practice, but it does not eliminate the hazard of choosing to enter avalanche terrain. Stick to lower angle, supported terrain, and places well away from large, steep, open slopes.
We have received a lot of snow over the past few days. These are the conditions when tree well and snow immersion suffocation accidents occur. Don't travel alone, and keep eyes on your partners. Check out https://www.deepsnowsafety.org/ for more information.Â
Snowpack Discussion
Regional Synopsis coming soon.
Avalanche Problems
Storm Slabs
Use extra caution around any slope steeper than 35 degrees. Avoid drifts and steer around areas where the wind has stiffened the snow on leeward slopes at mid and upper elevations. Wind loaded slopes could produce larger and more dangerous avalanches. Increasing easterly winds on Thursday will blow snow and create fresh slabs. Look for shooting cracks, recent avalanches, and use hand shears to check how the new snow is bonding to the underlying surface. Is there strong over weak, or are you seeing shooting cracks? Then there is slab structure. Avoid unsupported convex rolls and recently wind loaded locations. Continue to watch for loose dry avalanches - they could knock you off your feet or pile up debris deeper than you expect.
Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. Storm-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.
You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.
Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Likely
Expected Size: 1 - 1
Persistent Slabs
Near Washington Pass, a recently buried layer of facets may be found underneath the new snow on a variety of aspects. This layer looks to become a lasting problem. Look out for slab structure, especially in recently wind loaded areas, and check for weak snow underneath the slab. Step back and give the snowpack time to adjust while we collectively discover more about this recently buried layer.
We have less information about areas near, east, and south of Mazama. Persistent slab avalanches may be in play in these areas where recent snow may have fallen on a weaker snowpack. Watch for cracking, listen for collapses, or dig down to look for these layers of concern. If you can find layers of facets or surface hoar, all you need is a slab on top, and you have a recipe for dangerous avalanches.
Release of a cohesive layer of soft to hard snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slabs.
The best ways to manage the risk from Persistent Slabs is to make conservative terrain choices. They can be triggered by light loads and weeks after the last storm. The slabs often propagate in surprising and unpredictable ways. This makes this problem difficult to predict and manage and requires a wide safety buffer to handle the uncertainty.
This Persistent Slab was triggered remotely, failed on a layer of faceted snow in the middle of the snowpack, and crossed several terrain features.
Persistent slabs can be triggered by light loads and weeks after the last storm. You can trigger them remotely and they often propagate across and beyond terrain features that would otherwise confine wind and storm slabs. Give yourself a wide safety buffer to handle the uncertainty.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Likely
Expected Size: 1 - 1