Avalanche Forecast
Regions: Cascades - North West.
An extended warm spell continues to weaken the snowpack and cornices each day. There's a chance that point releases or cornice failures could trigger larger and more dangerous slab avalanches above treeline. Simplify the complex picture by reducing your exposure to steep sun-affected slopes, adjusting your aspect as the snow surface becomes moist or wet.
Discussion
Mild temperatures Sunday night followed by light winds with skyrocketing temperatures into the upper 40’s on Monday produced a handful of small and several large loose wet avalanches on sun-affected slopes opposite Mt. Baker Ski Area.Â
One particularly notable slide occurred on the SW face of Goat Mountain late Monday afternoon. A point release from rocks traveled 500-1000 ft and triggered a large wind slab (size 2+, R3+) at 5500 ft on a relatively low angle slope.
On Saturday, a snowmobile triggered a large wind slab avalanche near Bearpaw Mountain on a NE aspect above treeline after multiple passes on the same slope. One rider was caught and carried but not injured.
Large snowmobile triggered wind slab avalanche near Bearpaw Mountain (NE, 5800ft) HS-AM-R2-D2-U. One rider was caught and carried but uninjured. 03/14/20. Photo: Chris Macdonald
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
Loose Wet
A warm dry spell continues and the mountains are beginning their annual transition to spring. The result? Wet avalanches and cornices weakening to the point of failure, but it’s very difficult to predict when the large avalanche activity will “go off,” becoming more widespread. We think that thin clouds and slightly cooler temperatures may reduce avalanche activity slightly on Tuesday, but there’s plenty of uncertainty in this forecast. Follow a few rules of thumb to stay safe: (1) Avoid exposure to steep avalanche slopes during periods of strong sunshine and warm temperatures. (2) If it feels warm, the snow probably feels warmth as well, so check the snow surfaces for moist or wet snow more than several inches deep and adjust your aspect to find cooler slopes. (3) Plan for a rapid increase in avalanche activity from late morning through the afternoon hours.
Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.
Several loose wet avalanches, and lots of pinwheels and roller balls.
Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.
Aspects: East, South East, South, South West, West.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 1
Wind Slabs
Strong and variable winds redistributed storm snow into wind slabs at upper elevations since the last snow event March 10-11, so you will find wind-affected snow on a variety of aspects. There’s a chance that loose wet avalanche activity and gradually softening cornices may fail, giving stubborn old wind slabs the natural large triggers they need to be reactive on Tuesday. Distance yourself from sun-affected snow or overhung cornices above wind-textured snow these large "triggers" may create widely propagating large avalanches. Expect wind slabs to grow larger and easier to find as you gain elevation or move into more wind prone areas. Some of these slabs may be hard slabs that break widely and behind you, making them especially difficult to escape. Travel cautiously on polar aspects as well: carefully look and feel for evidence of wind drifted snow or hollow snow.
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.
Likelihood: Possible
Expected Size: 1 - 1