Avalanche Forecast
Regions: Cascades - East.
Travel in avalanche terrain is not recommended as very dangerous avalanche conditions in the Wenatchee Mountains. You will be able to trigger large avalanches at all elevations with natural and remotely triggered avalanches possible on wind loaded and leeward slopes. It will be essential to stick to lower-angle slopes and put a large buffer of terrain between where you travel and slopes steeper than 30 degrees.
Discussion
Saturday Update, 8am
By 7am on Saturday, Mission Ridge had received over 16 inches of snow. On Friday, observers reported triggering very shallow slab avalanches in the new snow at most elevations. A notable observation was a remotely triggered avalanche on a north aspect at 6,200ft. Expect even more reactive and dangerous conditions on Saturday.
The unique character of this storm is focusing on the Wenatchee Mountains. Prior to this storm, snow cover was very shallow. Stumps, logs, and rocks may be shallowly buried under the new snow. Use caution not to run into these obstacles. Areas closer to the Cascade Crest like the Teanaway, Icicle, and Entiat drainages, as well as the area around Holden Village, will likely experience less dangerous conditions. The avalanche problems may be similar but those locations will receive less snow.
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
The most dangerous slopes will be above treeline where both natural and triggered avalanches are likely. Expect dangerous and reactive avalanche conditions at all elevations. Put a large margin between where you travel and slopes over 30 degrees, especially where you see deeper drifts and pillows of snow. Triggering avalanches is most likely on leeward, wind loaded terrain. You may also be able to trigger avalanches in the new snow on wind-sheltered slopes below treeline. Watch for natural avalanches, cracking in the snow, and whumpfing collapses as indicators of the danger. Keep your terrain decisions conservative and simple.
Strong northeast and east winds are drifting significant amounts of new snow. The Wenatchee Mountains around Blewett Pass and Mission Ridge could receive storm totals nearing 2 feet of snow by the end of Saturday. Drifts could be at least 3 feet deep on leeward sides of ridges. Slick crusts and weak old snow are on many old surfaces and have already produced human triggered avalanches. Be suspect of the new/old snow interface as well as mid-storm layers for producing avalanches. If you don't see obvious signs of instability, use small, inconsequential test slopes to see how easily the new snow can slide.
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: All elevations.
Likelihood: Likely
Expected Size: 1 - 1