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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.

New winter like layers should be seen mainly near and above treeline on Friday. But spring snow conditions are also possible on solar slopes.

Detailed Forecast

A slow moving weak cold front will cross the Northwest Thursday afternoon and evening. This will cause increasing winds and increasing rain or snow. A weak upper short wave, cooler air mass and mostly light showers should follow across the Northwest on Friday. The main new snow Friday morning should be on the volcanoes.

Now that it is April and with new snow solar effects are likely to cause wet loose snow avalanches on solar slopes. This should be most likely on solar slopes above and near tree line where there was the most snowfall but watch for it in all the elevation bands. Watch for pinwheels and surface wet snow deeper than a few inches on any solar slope.

New wind slab which should be likely on lee slopes. This should be mainly north to southeast slopes near and above treeline. Watch for signs of cracking or firmer wind transported snow and approach open lee slopes with caution.

Shallow new storm slab should also be possible on more sheltered slopes mainly near and above treeline. This is most possible in areas that receive more than a few inches of snow. 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. An avalanche cycle started Friday and there were a couple close calls over the 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 Friday.

A fair period with warmer daytime temperatures and cooler night time temperatures was seen most of this week.The overall cool temperatures may be limiting wet loose avalanches. NWAC observers Jeff Hambelton, Dallas Glass and Tom Curtis reported mostly small wet loose snow avalanches from Mt Baker, Mt Rainier and Mt St Helens on Wednesday. The ski areas have not reported any significant avalanches so far on Thursday.

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.