Avalanche Forecast
Regions: Cascades - North West.
Dangerous avalanche conditions exist due to new snow and wind. You are most likely to trigger large avalanches on steep, shaded northwest through northeast aspects and where you see freshly drifted Wind Slabs. Steer around recent drifts and deeper pillows of snow on steep, wind exposed slopes. Take time to carefully evaluate layers in the top 2 feet of the snowpack and watch for obvious signs of instability like recent avalanches and cracks in the snow.
Detailed Forecast
You can trigger avalanches, on Monday, due to new snow and wind forming slabs over a thin layer of buried surface hoar. These avalanches could be big enough to bury or kill you. You can trigger Wind Slabs at upper elevations on leeward sides of ridges and terrain features. Watch for cracking in the snow, wind-sculpted features, and thick pillows of snow as indicators of the Wind Slab snowpack structure. Steer around these features to avoid triggering these avalanches.
Near and below treeline the new snow is falling on slick surface crusts. You can trigger storm slabs on slopes over 35 degrees where you find more than 6 inches of recent, cohesive snow that slides easily on the old surface.
Any avalanche today has the potential to involve a dangerous buried weak layer of surface hoar. This layer exists in the top two feet of the snowpack, mostly on northwest through northeast shaded slopes. Digging below the surface and using snowpack tests can help you identify this layer. Old, weak snow layers exist over 6 feet below the surface. It's been weeks since any reported avalanches involved these deeper weak layers
Snowpack Discussion
Observers have reported at least five triggered avalanches since Friday in the Mount Baker area. These have occured on mid to upper elevation slopes where the wind has drifted slabs in the past five days. Profiles at the crown of some of these avalanches on north and east aspects have indicated the 3/25 surface hoar as the weak layer. We are currently dealing with avalanche problems related to the recent storms and blowing snow, but you may experience these avalanches breaking in surprisingly reactive ways. use snow pits and tests to monitor these avalanche problems and the potential for them to persist into the future. Buried surface hoar should show up as a thin stripe 1-2.5 feet below the snow surface on shaded, northerly slopes above 5,000ft. Time will be the judge whether this weak layer remains a problem for triggering avalanches after the storm instabilities stabilize.
Six to eight inches of snow fell by late Sunday, with over a foot possible by the end of the day Monday. Snow has fallen on a variety of surfaces including slick crusts and surface hoar. Freshly forming Wind Slabs could be adding to the stacks of slabs on top of the 3/25 surface hoar. Moderate winds formed older slabs last Wednesday near and above treeline. Many slopes have crusts formed in the top 2-3 feet of the snowpack. At higher elevations and shaded slopes dry soft snow can still be found.
Below the top 2-3 feet, the snowpack is generally well rounded and lacking interfaces of concern. The old 2/8 melt-freeze layer can still be found over 6 feet (200cm) deep in the snowpack. While this layer isn't listed in our current avalanche problem set, it may reawaken if it becomes wet.
Observations
North
On Friday, NWAC Observers Lee Lazara and Simon Trautman traveled in the Bagley Lakes area. They reported 3 triggered or natural avalanches about 1 foot deep on north aspects near treeline on slopes with recently drifted snow. The observers found a thin weak layer buried 3/25 at the interface of concern.
On Wednesday Mt Baker Ski Patrol reported 8-12 inches (20-30cm) of soft snow over a recent melt-freeze crust. This snow was very rapidly effected by small sun breaks and thinning in the clouds. Winds earlier in the weak formed new wind slabs at higher elevations.
Avalanche Problems
Wind Slabs
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
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: Likely
Expected Size: 1 - 1