Avalanche Forecast
Regions: Olympics.
As the storm winds down Saturday, be on the lookout for slopes where the wind drifted the new snow into firmer and thicker slabs. These are the places where you’re most likely to trigger an avalanche. Fresh cornices, textured surfaces, and deeper snow deposits can clue you into wind loaded areas.
Discussion
There’s some uncertainty around the avalanche forecast for the Olympic Mountains on Saturday. Some weather models hint that upslope snow showers off the Strait could produce locally heavier snow accumulations in the northern Olympics. If that occurs and more than 6-8†of snow falls overnight, then you could encounter locally higher avalanche danger.Â
As of Friday afternoon, about 4†of low-density, unconsolidated new snow had accumulated at Hurricane Ridge. This new snow fell on a variable old surface including firm crusts, wind packed snow, weak facets, and soft old powder. It may be hard to say what’s underlying the storm snow on any given slope, but typically firm crusts were found on S-W aspects and softer, weaker snow were seen on N-E aspects. You may find the new snow reacts differently as you change from one slope to the next.Â
You can see a wide variety of snow surfaces prior to the storm. Maggies. W aspect, 5300’: Photo: Matt Schonwald
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
Wind Slabs
Winds should increase and peak overnight, easily transporting the light dry snow. Keep your eyes open for slopes where the wind formed firmer and deeper slabs. Fresh cornices, drifts behind trees, and textures surfaces can point toward wind loaded areas. Steer around terrain greater than 35 degrees if you suspect a wind slab may exist. As you ascend in elevation, these slabs could grow larger and more difficult to manage.
In areas sheltered from the wind, the new snow may not bond well to the old surface. You could trigger loose avalanches that despite there small size run far and fast. Don’t let them catch you off guard.
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.
Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..
Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.
Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1