Avalanche Forecast
Regions: Stevens Pass.
The avalanche danger should decrease with lingering wind and storm slab the main avalanche problems on Monday.
Detailed Forecast
Light northeast winds, clouds giving way to some sun and cool temperatures should be seen west of the crest on Monday.This should cause stabilizing and a decreasing avalanche danger on Monday.
Lingering wind slab will be rated as likely west of the crest on Monday. Watch for firmer wind transported snow on steep lee slopes.
Lingering storm slab may still be possible on Monday so watch for it in any areas that received heavier amounts of snow. Hand shears or shovel tilt tests can be fast ways to check for this type of layer.
Any hoar frost that survived the storm would increase the instability of wind or storm slab layers.
Instability should be limited to new snow and deeper instabilities in the snow pack are not currently expected west of the crest.
The sun should be out by later Monday but sun effects should be limited since we are barely past the solstice.
Note that northeast winds may increase Monday night and Tuesday so heads up for new wind slab potential on Tuesday.
Snowpack Discussion
A cooler period with little precipitation was seen about Thursday to Friday. NWAC observer Dallas Glass saw widespread 5 mm surface hoar which formed around Paradise Thursday night.
Sparkly surface hoar on a SW aspect at 6000 feet at Paradise Friday by Dallas Glass.
A cold front moved over the Northwest on Saturday and Saturday night. West winds changed to northwest, with moderate to heavy snow west of the crest and a cooling trend. Convergence contributed to snowfall in the central Cascades. NWAC sites west of the crest picked up about 6-14 inches of new snow by Sunday morning.Â
Northwest winds are decreasing west of the crest on Sunday with little or no snow accumulation and cooler temperatures. NWAC observer Tom Curtis at Stevens Sunday morning reported natural storm slab avalanches due to heavy loading. By Sunday afternoon NWAC observers Jeff Hambelton at Baker and Jeremy Allyn at Crystal reported improved stability with mostly right side up uncohesive snow. So the cooling trend looks like it favored right side up snow and should help limit the extent and longevity of new slab layers.
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: North, North East, East, South East, South.
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.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 1