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Avalanche Forecast

Archived

Apr 4th, 2014–Apr 5th, 2014

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

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. 

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.

Problems

Loose Wet

Loose Wet avalanches are the 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. 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.

Wind Slabs

Wind Slab avalanches are the 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.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). 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.