Avalanche Forecast
Regions: Stevens Pass.
Travel in avalanche terrain is not recommended Wednesday.
Detailed Forecast
Another stronger front will cross the Northwest Tuesday night to Wednesday morning. This should cause stormy weather with strong west to southwest winds, heavy rain or snow and warming temperatures.
New wind slab will be likely in the higher elevations zone on lee slopes and storm slab will be likely on a wider variety of aspects. The warming temperatures will further build upside down heavier snow over initial lower density snow and weak surface snow from last week. Wind and storm slab may continue to release on layers from last weekend or on weak layers from last week. Buried surface hoar and crust layers from January may be available to act as a weak layer and bed surface.
Rain at lower elevations will also load and weaken surface snow layers and may cause wet loose avalanches in the lower below treeline zone.
Natural and triggered avalanches should be likely Tuesday night and Wednesday. Travel in avalanche terrain is not recommended Wednesday. The avalanche danger may decrease by later Wednesday. But another less defined front may maintain these conditions much of Wednesday so there is uncertainty in the forecast later Wednesday.
Limited snow at the lowest elevations will limit the avalanche danger there. The mid and base pack should still consist of mostly stable crust and melt form layers from periods of warm weather earlier this winter.
Snowpack Discussion
Last week very cold temperatures produced a variety of weak surface snow conditions including surface hoar, near surface faceting and preserved the generally light amounts of low density snow that fell last week. These layers should cause the avalanche danger to significantly increase this week as vigorous fronts move across the Northwest and snow and rain bury and load these layers.
NWAC observer Jeff Hambelton at Mt Baker on 6 February found low density snow and a crust from January that should be the types of layers that will be weak and act as a bed surface this week:https://www.youtube.com/watch?v=N_uMXEKsyvM Â
A cold front moved across the Northwest on Monday afternoon causing west to southwest winds, moderate to heavy snow, and a warming trend. The front eroded the cold air mass east of the crest. Snowfall ending Tuesday morning was mostly in the 5-20 inch range west and east of the crest. This built upside down heavier snow over initial lower density snow and weak surface snow from last week. Back country reports are few but extensive 1 foot natural and triggered storm slab avalanches were reported by the Mt Baker and Alpental ski patrols late Monday to Tuesday morning. Slabs are releasing on layers from last weekend and likely on weak layers from last week.
NWAC observer Jeff Hambelton sent this photo of a storm slab triggered on a test slope at Mt Baker from 10 Feb.
Also just in late Tuesday afternoon - NWAC observer Jeff Ward in the Stevens Pass area reports further ski triggered collapsing of late January surface hoar layers. And the Stevens Patrol reports that a skier near the ski area triggered a slab avalanche of about 20 inches that released in late January crust and buried surface hoar layers. So the recent and new denser snow may be loading and re-activating late January layers where they are present. This should be mainly near Stevens Pass and possible Snoqualmie Pass for the region near and west of the crest.
Avalanche Problems
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: Likely
Expected Size: 1 - 1
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.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 1
Loose Wet
Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.
Several loose wet avalanches, and lots of pinwheels and roller balls.
Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.
Elevations: Below Treeline.
Likelihood: Possible
Expected Size: 1 - 1