Avalanche Forecast
Regions: Cascades - South West.
Just as avalanche conditions were slowly lowering, here we go again. Another round of East winds will re-distribute recent heavy snowfall onto unusual aspects. Wind slabs may develop on open slopes below treeline. Pay attention to loading patterns; aspects that were recently drifted may become stripped by the end of the day. Stay safe by choosing less wind affected and moderately angled terrain.
Discussion
Snow and Avalanche Discussion
Staying safe on Thursday requires thinking about a mix of new and old avalanche concerns. Rather than trying to manage a complex scenario, choose simpler terrain not capable of producing large avalanches.
An amazing amount of snow, 4-5 feet, has fallen in the West Slopes South zone since the weekend, with the storm cycle peaking Monday night and Tuesday. These storm numbers alone should raise your avalanche alarm bells!Â
Natural and triggered slab avalanches that were widely reported in the Crystal area Tuesday were generally less reactive and widespread by Wednesday. Very little natural or skier triggered avalanche activity was reported in the White Pass area. Paradise has been closed for several days due to winter storm conditions.Â
It's important to note we have had limited field observations over this stretch due to the strong storm conditions. Based on the information we do have, all the recent snow is sitting on a hard crust, but unlike in adjacent forecast zones, a weak snow(facet)/crust combo isn't widespread and/or reactive.Â
We've received a lot of snow over the last few days. The risk of tree well and snow immersion suffocation is real in the trees. Don't travel alone and always keep in contact with your partner. You can learn more about deep snow safety here.
Snowpack Discussion
New Regional Synopsis coming soon.
Avalanche Problems
Wind Slabs
We know East winds build wind slabs on unusual aspects and that's there's plenty of snow available to be transported by the forecast winds. To avoid triggering a wind slab avalanche, approach steep unsupported slopes with wind-drifted snow cautiously, feeling for firm or hollow sounding snow as a sign that wind slabs may be present. You can stay safe by traveling on ridges, wind-scoured areas and slopes less 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
Storm Slabs
Storm slab instabilities from recent heavy snow are healing, but in areas where they are poorly bonded to an underlying hard crust, large slab avalanches remain possible. Give recent storm snow time to settle by sticking to moderately angled and supported slopes.
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.
Elevations: Treeline, Below Treeline.
Likelihood: Possible
Expected Size: 1 - 1