Avalanche Forecast
Regions: Stevens Pass.
A continued mix of winter like and spring conditions should be seen Saturday. The timing and strength of the incoming front on Saturday will be important for avalanche concerns on Saturday.
Detailed Forecast
A front with increasing clouds and moisture will move to the Northwest Saturday afternoon and night. This is expected to cause increasing winds and increasing rain and snow with slightly rising snow levels first in the Olympics Saturday early afternoon and in the Cascades Saturday late afternoon. The timing and strength of this system will be important for avalanche concerns on Saturday. If the system arrives sooner than expected then new wind slab and storm slab will begin to form sooner in the day. If the system arrives later or weaker then significant new wind slab and storm slab may not form before the end of the daylight hours.
After solar effects, avalanches and consolidation today and overnight cooling tonight the avalanche danger will be lower Saturday morning.
Clouds should increase over the Cascades on Saturday and cut down on solar effects compared to Friday. So wet loose avalanche activity should be less on Saturday. But wet loose avalanches will be listed as possible on Saturday. This should be mainly on solar slopes in all the elevation bands near and west of the crest. Watch for natural avalanches, pinwheels and surface wet snow deeper than a few inches on any solar slope.
The formation of new wind slab as mentioned above depends on the timing and strength of the incoming system. The formation of new wind slab on lee slopes is expected to be likely by the end of the daylight hours in the Cascades. This should be mainly north to southeast slopes near and above treeline. Watch for signs of cracking or new firmer wind transported snow and approach open lee slopes with caution.
The formation of new storm slab as mentioned above also depends on the timing and strength of the incoming system. The formation of new storm slab is also expected to be likely by the end of the daylight hours in the Cascades. This should be mainly on sheltered slopes near and above treeline in areas that receive more than a few inches of snow by the end of the day. Storm slab forms where bonds are poor to previous snow or where wind or where temperature changes create temporary weak storm layers.
Remember to watch for cornices if you venture onto ridges and avoid slopes below cornices. Cornice failures are often seen during the transition to spring weather. Cornices have grown large recently and may break back further from the edge than expected.Â
Snowpack Discussion
March ended with a return to winter. A storm cycle peaked last weekend and delivered about 1 to 3.5 ft of snow at NWAC stations near and west of the crest. This caused an avalanche cycle and there were a couple close calls last weekend. Skier triggered storm slabs were reported in Silver Basin near Crystal on Saturday via the NWAC observation page. A skier via TAY in the Tatoosh Range reported triggered storm slabs up to 1 foot one of which caught another skier. Luckily no injuries were reported.
An upper low sank south off the coast early this week and largely missed the Northwest. But locally strong east winds were seen mainly near and above treeline and mainly in the south Cascades. NWAC observers Tom Curtis on Mt Adams Tuesday and Dallas Glass on Mt. Rainier on Wednesday reported redistributed snow and cross loaded slopes. Dallas reported 20-40 cm of wind slab in the 6400-7500 foot range with natural avalanches on a variety of aspects. This older wind slab will not be listed as a concern due to anticipated new wind slab but continue to watch for it on Saturday.
A fair weather period with little avalanche activity was seen mid-week.
A front crossed the Northwest on Thursday causing moderately increasing winds, varied amounts of new snow and slightly lower snow levels. New snow amounts varied from 15 inches at Mt Baker, 9 inches at Paradise to 4 inches at the top of Alpental.
The main reports today come from a couple of the ski areas. The Mt Baker ski patrol reports widespread ski triggered 10-14 inch storm slab above about 4000 feet. The Alpental ski patrol reports widespread natural and ski triggered wet loose avalanches some large in the Source Lake valley above about 4000 feet.
Avalanche Problems
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.
Aspects: South East, South, South West.
Elevations: All elevations.
Likelihood: Possible
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
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: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 1