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Avalanche Forecast

Archived

Apr 1st, 2014–Apr 2nd, 2014

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

Regions

Stevens Pass.

By Wednesday, the latest storm snow will be at least 3 days old and weaknesses in storm layers will have likely settled and stabilized, especially on solar aspects.  Conintue to watch for earlier wind slab deposits on steeper non-solar aspects at higher elevations, but mainly watch for solar effects on the recent snow on steep exposed terrain.  

Detailed Forecast

A weak upper ridge should move across the area Wednesday, causing further clearing with little change in freezing levels.  However, solar effects should cause significant daytime warming.  This should again lead to mainly wet snow avalanche concerns.  

As the older storm slab and wind slab layers continue to settle and stabilize Wednesday, the main concern should be mainly wet loose avalanches on steep sun exposed terrain. This should be likely on solar slopes in all three elevations bands and may be also possible on non-solar slopes. Watch for wet surface snow deeper than a few inches, roller balls in surface snow and small natural wet loose releases that usually precede more major wet loose snow avalanches. Avoid terrain traps where a small but powerful wet loose avalanche could have unintended consequences.

Continue to watch for areas of recent wind slab on lee slopes. This is likely on shaded north to east slopes near and above treeline. Watch for signs of cracking or firmer wind transported snow and approach open lee slopes with caution.

Remember to watch for cornices if you venture onto ridges Wednesday and avoid slopes below cornices. Cornice failures are often seen during the transition to spring weather.

Snowpack Discussion

A wintery weather pattern was renewed over the Northwest starting last Tuesday until about midday Sunday. About 1-3.5 feet of snow fell  at NWAC stations near and west of the crest between last Tuesday and Sunday with less snow at lower elevations.

Avalanche conditions also became active through the weekend.  We are now seeing a mix of winter snow conditions mainly on shaded slopes at higher elevations and spring snow conditions on solar slopes and at lower elevations.

Little or no new snow has fallen since Sunday with periods of sunshine and afternoon temperatures climbing to the low 40's allowing storm weaknesses to quickly settle and stabilize.  About 6-10 inches of snowpack settlement have occurred over the past 2 days indicating that recent storm weak layers are also settling and stabilizing.  

While we have been in a stabilizing pattern going on three days come Wednesday, making human triggered slides much less likely, there still may be some unstable wind slab or storm slab conditions remaining, especially higher elevation shaded slopes where stabilization has been slower. Continue to choose conservative terrain, watching for previous wind deposits.

No recent avalanche activity has been reported or observed over the past few days, but here are some reports from the weekend and late last week.

NWAC observer Jeff Hambelton was near Church Mountain along the Mt Baker highway on Wednesday 3/26 . He saw several small but natural and human triggered storm slab avalanches on lee aspects near treeline likely failing within the new storm snow. He was at Table Mt near the Mt Baker ski area on Thursday and saw widespread natural wet loose avalanches on all aspects with solar effects and daytime warming.

Storm slab on Church Mtn 26 March by NWAC observer Jeff Hambelton.

A front crossed the Northwest on Friday. The Mt Baker ski patrol reported large skier triggered wet loose avalanches on Friday. The Alpental ski patrol and Snoqualmie DOT reported a natural cycle of loose snow avalanches on late Friday which were drier in the upper elevations and wetter at the lower elevations. NWAC observer Tom Curtis was at White Pass on Friday and reported 4-8 inch wind slab conditions at about 5800 feet.

Wind slab conditions near White Pass on 28 March by NWAC observer Tom Curtis.

Reports from over the weekend include the following. Ski cuts Saturday at the Mt Baker ski area gave mainly isolated wet loose avalanches below 4000 feet. NWAC observer Jeff Hambelton on the west side of Mt Baker Saturday reported building wind slab above about 6000 feet. The Alpental ski patrol reported a natural cycle of loose snow avalanches on Saturday night. Sunday the Mt Baker and Alpental ski patrols reported isolated 4-8 inch storm slab avalanches releasing in storm layers.

Multiple snowmobile triggered storm slabs on W-NW aspects near tree line were observed on Grouse Mountain near Mt Baker Sunday, 3/30 by NWAC observer Jeff Hambelton. The failures remained in the latest 24 hour storm snow and did not step to reactive weak layers experienced Saturday. Photo: J. Hambelton 

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.