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RegisterMar 30th, 2017–Mar 31st, 2017
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The avalanche danger will be rated higher in the Mt. Baker area where more recent snow has accumulated, especially in the higher terrain. Loose wet avalanches will be increasingly likely Friday, where small wet snow avalanches may entrain deeper wet snow layers and become large. Use caution in steep sun exposed terrain during the warmest part of the day, avoiding steep slopes above terrain hazards such as trees or cliffs. Large recent wind deposited snow at higher elevations will maintain the low probability/high consequence potential for very large avalanches above treeline.
High pressure is expected to rebuild over the area Thursday night through Friday. This will cause clearing overnight and allow for wet surface snow to begin refreezing and strengthening.
Partly to mostly sunny conditions Friday and warming temperatures should cause a gradual increase in danger from wet snow avalanches, especially on slopes receiving direct sun and during the warmest part of the day.
Recent shallow wind slabs should continue to settle and stabilize where formed on lee slopes, mainly above treeline and on NW-SE aspects.
The danger will be rated higher in the Mt. Baker area where once again, more snow fell with a cooling trend Wednesday afternoon through Thursday. Snow levels were regionally lower in the northwest zone during this event, maintaining the low probability/high consequence potential for very large avalanches above treeline and large wet snow avalanches below treeline.
The expected clearing and cooling overnight Thursday should cause a strengthening surface crust by Friday. However, if previously wet surface snow has not refrozen, be suspicious of loose wet avalanches that may begin small but entrain older snow and become dangerous and difficult to manage. Pay particular attention to steep solar facing slopes above terrain traps such as trees, cliffs or gullies where being caught and carried, even in a small slide, could prove consequential.
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.
Recent Observations
North
On Wednesday the Mt Baker pro - patrol reported widespread storm slab and loose wet avalanches below 4500 feet during morning control work. 1 large natural avalanche was observed off Shuskan Arm. Start zones above 5000' were stubborn to trigger during early morning control work, but likely became more sensitive as warming pushed the snow-line higher during the day.
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.