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RegisterMar 31st, 2017–Apr 1st, 2017
Stevens Pass.
Loose-wet snow avalanches should remain possible in steep terrain. Use caution in steep terrain, especially if the surface snow is wet more than a few inches, avoiding steep slopes above terrain hazards such as trees or cliffs. Avoid travel on or below cornices.
A warm, sunny day Friday allowed for further shallow melt and consolidation. Increasing clouds Friday night with light precipitation should maintain mild temperatures and allow for limited surface crust formation.
This weather should maintain shallow, moist to wet surface snow conditions Saturday.
Only light amounts of additional precipitation with a gradual cooling trend are expected Saturday. This should not appreciably change the overall avalanche danger through the day Saturday.
Expect shallow wet snow conditions over one or more strong near surface crust layers.
Recent shallow wind slabs should have mostly stabilized where formed on lee slopes, mainly above treeline and on NW-SE aspects.
Recent cornices are very large. Natural cornice releases and resulting slab avalanches are dangerous and unpredictable. Give cornices a wide berth if traveling along ridge-lines and avoid slopes directly below large cornices. See a blog post regarding cornices here.
Special Note: For more information on the massive natural cornice triggered avalanche on the north side of Ruby Mountain on Sunday 3/19 and general thoughts about low-likelihood/high consequence avalanches, please see NWAC's blog post issued, Sunday, March 26.
Weather and Snowpack
Let's just say it's been a wet and wild few weeks regarding weather and avalanches in the Cascades.
This past week has also been active weather-wise, but water amounts/snowfall totals have been slightly lower relative to the extreme wetness of the past few weeks. In the last 5 days ending Monday morning NWAC stations near and west of the Cascade crest have picked up 1.5-4 ft of snow with the most at Mt. Baker and above the Pass levels.
A strong low pressure system brought rising snow levels and locally heavy precipitation Tuesday night through Wednesday along the west slopes of the Cascades. Most ski areas and DOT programs checked in reporting natural and explosive controlled avalanches in their area of responsibility. The most snow was received at Mt. Baker (2 feet) and Paradise (14 inches) with more moderate amounts elsewhere before changing to rain on Wednesday.
Cooling and showery weather Thursday allowed wet snow to begin refreezing with an additional 3-6 inches accumulating in most areas. The winds diminished by Thursday and combined with daytime warming, this has allowed for recent wind slabs to begin stabilizing.
Very mild temperatures and increased solar radiation Friday allowed for wet surface snow conditions in most terrain, even northerly facing slopes. Shallow loose-wet snow avalanches occurred Friday on many steep slopes but remained small.
Recent Observations
North
On Friday, NWAC's Lee Lazzara was in the Mt Baker backcountry and reported a large number of loose-wet avalanches in many areas had released recently, likely during rain Wednesday or warming Thursday. Several large slab avalanches likely released Wednesday as well. Deep rain runnels were throughout the terrain to about 4800 feet with about a 4 inch supportable surface crust as of Friday morning. By afternoon shallow wet surface snow was making loose wet avalanches possible on steeper terrain.
Central
On Wednesday Alpental pro-patrol reported widespread natural and explosive triggered storm slab avalanches late morning. Loose wet avalanches on the lower half of the mountain were beginning to entrain deeper layers. Snoqualmie DOT reported large natural avalanches (up to size D2.5) running in start zones above 4500 feet late Wednesday morning. Stevens Pass DOT reported large slides during control work Tuesday night with avalanches gouging down to deeper layers.
South
Crystal pro-patrol reported sensitive 4-8" storm slab on the upper half of the mountain Wednesday morning. A widespread but shallow natural loose wet cycle was observed in the surrounding backcountry later in the day with continued warming.
NWAC's Jeremy Allyn travelled above Paradise Friday to well above the forecast elevations. A strong, supportable near surface crust was encountered at least to about 8000 feet with about 4-5 inches of recent storm snow above. This shallow surface snow shed from the steeper slopes as loose wet avalanches by midday under sunny, warm weather. Several larger slab releases were noted in the Tatoosh and Mt Rainier proper, likely releasing during the rain event this past Wednesday.