Avalanche Forecast
Regions: Cascades - East.
New snow may begin to accumulate rapidly, and avalanches may become easy to initiate on steep slopes as the day progresses. Expect dangerous conditions to form by the evening with an increase in winds and heavy snowfall. If you find more than 8" of new snow along with signs of instability, expect the avalanche danger to be Considerable, so avoid steep slopes.
Discussion
The day will begin with Low avalanche danger and may become Considerable by days end in some areas. Snowfall will begin in the morning and increase by mid day. By the end of the day we can expect up to 8" of new snow in the favored east to west oriented Wenatchee Mountains. Snowfall, winds, and avalanche danger will increase into the evening hours. Blewett Pass and Mission Ridge stand to do quite well and may receive well over a foot of new snow by Saturday morning. Avalanche danger will be directly tied to the amount of new snow that falls, and how well this snow bonds. Observations from Mission Ridge and Colchuck Lake speak of stout sun crusts, breakable wind crust, hard wind slab, and weak faceted snow or surface hoar on some shaded slopes in the mid elevations. The new snow may hide previous textures, making for slick, and tricky travel conditions. If you get out on Friday, take note of how the new snow is bonding and as always, share your observations with us!
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Snowpack Discussion
March 12, 2020 (The regional synopsis is updated every Thursday @ 6 pm)
From March 6th to the 12th the Pacific Northwest experienced a few small storms and a few notable days for people and avalanches. Light to moderate snow accumulated slowly over a period of a few days, and avalanche danger increased from Low to Moderate over the weekend of March 8th. The exception was the West North zone, which won the snowfall competition this week. 18-24†of new snow was observed in the Mount Baker area on the 6th, and 10†of new snow on the 11th. Avalanche danger reached Considerable there for storm slab, wind slab, and loose wet avalanche problems.Â
People, complicated avalanche terrain, and lots of avalanches. Bagley Lakes Basin, West North zone. Photo by Nathan Resick, March 8, 2020.
Loose dry slides initiated by skiers in big terrain. No one was caught or carried. East Central zone. March 8, 2020. Matt Primomo photo.
The snow fell with minimal wind, and accumulated slowly over firm suncrusts or wind stiffened surfaces. Thicker cloud cover inhibited the sun in areas where 4†to 12†of snow accumulated over the course of a few days. Cold overnight temperatures allowed the low density snow to weaken. By the 8th, the clouds broke up enough to allow strong radiation to change snow surfaces. When the sun finally did hit the snow, it quickly caused loose avalanches in steep terrain.Â
An active weekend for people and avalanches:Â
Many areas experienced some form of loose avalanche activity from March 6th to 9th. Sunday, March 8th was the day that recorded the most widespread avalanche activity across the region. The size of these avalanches were directly related to the amount of new snow that had recently accumulated in that area, and the size of the terrain.Â
West North zone on March 8, and West South zone on March 8th. Uphill and downhill tracks got covered by debris. Photos by Zack McGill and Dallas Glass.
We as a community can look back at, and learn from these few days. Numerous human triggered slides occurred, some were slabs but the majority were loose. A number of catch and carries were observed, and many more likely went undocumented. Luckily, no injuries or burials were reported. Observers across the region reported lots of instances where previous tracks got hit with debris, either from human triggered or natural avalanches.Â
As the days get longer and folks begin to step into the alpine zone and bigger terrain more frequently, it is important to keep a humble attitude. Continuously evaluate route selection with potential for loose wet and cornice falls in mind. Check the mountain weather and avalanche forecasts for the most up to date info. Enjoy the backcountry, be safe, and let us know what you see out there!
-MP
Solo snowboarder aired into this slope, and went for a ride but was not buried or injured. Slide took out the corner of a skin track. Bagley Lakes Basin, March 8, 2020, Zack McGill photo.
Wind slab triggered by a skier at 7,500ft next to the popular route on Mt St Helens. The skier wasn’t caught or carried. Andy Goodwin photo, March 8, 2020.
Avalanche Problems
Storm Slabs
Snowfall rates will begin to increase by the afternoon. Once over 5" of snow has accumulated, and if it begins to snow heavily, you should start to think "avalanche". Look for signs of instability such as shooting cracks and loose snow avalanches. Check to see how the new snow is bonding to older, slick surfaces. If you find signs of fresh avalanches, avoid consequential slopes steeper than 35 degrees. If you find more than 8" of new snow along with signs of instability, expect the avalanche danger to be Considerable, and avoid steep slopes.
Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. 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.
You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.
Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 1