Avalanche Forecast
Regions: Cascades - South West.
Don't be fooled on April 1st and watch for shallow yet sensitive slab avalanches involving new snow on lee easterly slopes near and above treeline as well as loose wet avalanches on solar slopes during sunbreaks and daytime warming Wednesday.
Detailed Forecast
Additional light snow accumulations are expected Tuesday night through Wednesday along the west slopes, except in the Snoqualmie/Stevens area where accumulations near and above treeline may be closer to a foot. Moderate westerly transport winds are expected to ease Tuesday night. Showers may be locally intense Wednesday afternoon due to the unstable air mass over the region.Â
Moderate danger means heightened avalanche conditions on specific slopes. Watch for shallow yet sensitive slab avalanches involving new snow on lee easterly slopes near and above treeline as well as small loose wet avalanches on solar slopes during sunbreaks and daytime warming Wednesday. Shallow slabs may fail on graupel layers from Tuesday. Higher avalanche danger is expected above treeline in the Stevens to Snoqualmie zones where more snowfall is forecast.     Â
Cornices won't be listed as an avalanche problem but be aware of new cornice growth along ridgelines.
Snowpack problems west of the crest for the time being should be in the upper or surface layers. The mid and lower snowpack west of the crest consists of layers of stable consolidated rounded grains or melt forms and crusts from multiple warm periods this season. Many areas at the lowest elevations do not have enough snow to cause an avalanche danger.
Snowpack Discussion
Winter-like conditions last week were followed by reports of natural and skier triggered loose avalanches on Tuesday, Mar 24th along the west slopes. This was followed by a warm front and heavy rain last Wednesday through Thursday morning. This caused an avalanche cycle west of the crest with many large natural avalanches observed in the Mt Rainier area above treeline.
A frontal system brought 2-3 inches of snow at higher NWAC stations west of the crest Friday night. The new snow was reported to have bonded well to the previously moist surface. Mt. Baker picked up another inch of water Sunday and Sunday night with snow levels 5-6000 ft while other locations experienced fair weather. Monday saw fair and mild weather with more snowpack settlement.Â
Snow levels fell quickly after a front moved through early Tuesday morning. Scattered showers through Tuesday afternoon had deposited a few inches near and above treeline along with moderate westerly transport winds. In many areas the old moist surface should be slowly re-freezing with the new snow generally bonding well, keeping avalanche concerns confined to new storm snow layers. Â
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.
Elevations: Alpine, Treeline.
Likelihood: Possible
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.
Aspects: East, South East, South, South West, West.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1