Avalanche Forecast
Regions: Cascades - East.
New snow instabilities within the deep recent snowfall will continue to settle out, but continue to make conservative terrain choices by choosing lower angled terrain and avoiding wind loaded slopes. Recently formed wind slabs may be found on a variety of aspects Tuesday. Travel with deep snow safety precautions in place.
Detailed Forecast
Showers should end or become widely scattered Tuesday morning. Cold temperatures and light winds are expected Tuesday. This should allow for slow settlement and stabilization of recent wind and storm slabs formed during the storm cycle since Friday.
Storm slabs may still be sensitive on Tuesday, but likely confined to the most recent storm snow over the past day. While deeper storm slab instabilities should be stabilizing, it may still be possible to trigger a large storm slab avalanche in isolated areas.Â
The unconsolidated snow is deep, so being aware that loose dry avalanches triggered on steep slopes can entrain substantial snow.  Â
Instabilities within the deep new snow may need more time to settle out so make conservative terrain choices by choosing lower angled terrain and avoiding any wind loaded slopes, mainly near and above treeline.Â
Note that deep snow conditions now exist in most terrain. Travel with a partner and use good communication and keep your partner in view at all times.Â
Lingering wind slabs will be the primary avalanche hazard near and above treeline.Â
Continue to investigate the snowpack and test for persistent weak layers (PWLs) in the snowpack, especially in areas further east of the crest with a shallower snowpack and on northerly aspects in the Washington Pass zone below the 1/17 crust.Â
Snowpack Discussion
Weather and Snowpack
A strong storm cycle began Friday with 2-3 feet of snow reported along the east slopes on average, through Monday afternoon with lesser amounts at lower elevations and in the Mission Ridge/Blewett area. A slow warming trend affected all areas Saturday afternoon.
Moderate W-SW winds occurred in the Washington Pass zone Saturday night. Light to moderate snow showers have been occurring through Monday afternoon in all areas.Â
Recent Observations
North
Persistent slab has been re-listed in the northeast zone highlighting a 5 cm layer of facets roughly 10 cm below the 1/17 crust in the Washington Pass zone and in areas further east. This reactive PWL has only been found in isolated locations, in cold non-wind affected north facing terrain. No avalanche activity has been observed on this layer.
NWAC pro-observer Jeff Ward was in the Varden Creek drainage Saturday and found 15-20 cm of storm snow well bonded to a variety of snow surfaces with the new snow generally lacking a slab structure. Small storm slab avalanches were only observed on steep solar aspects, likely failing on the most recent sun crust. Wind slabs on lee northerly aspects were the main avalanche problem with skier triggered avalanches possible near and above treeline. Â
On Sunday, Jeff and NCH observed debris from several small wind slab avalanches and one large wind slab avalanche, size D2.5, that ran from ridgeline over 2000 feet on a ENE aspect likely during peak precipitation and wind loading Saturday night. Storm slabs were not particularly sensitive in areas Jeff traveled, with evidence of a few previous natural storm slabs observed on steep solar aspects that likely ran on the 1/30 sun crust. Â
Central
Both Tom Curtis and Jeff Ward traveled independently in terrain east of Stevens Pass Wednesday 2/1, covering the areas of Rock Mountain, Jove and Union Peaks. Both reported rapidly forming, very touchy wind slabs by mid-morning Wednesday. Wind slabs were building much further downslope due to the strength of the winds. Wind slabs up to 12 inches were seen and noted forming well below treeline.Â
On Sunday, 2/5, ski patrol at Mission Ridge reported several collapses (whumpfs)Â on deeper weak layers. These occurred on an infrequently skied NE aspect about 6000 ft. Â
South -Â No observationsÂ
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, North West.
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
Persistent Slabs
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: Unlikely
Expected Size: 1 - 1