Stevens Pass Avalanche Forecast

Issued: Mar 15th, 2020 11:10AM

Sun Mar 15th Current Conditions
Alpine Moderate Treeline Moderate Below Treeline Moderate
Mon Mar 16th 2 Day Outlook
Alpine Moderate Treeline Moderate Below Treeline Moderate

The alpine rating is moderate, the treeline rating is moderate, and the below treeline rating is moderate. Known problems include Loose Wet and Wind Slabs.

Strong sun and warm temperatures will create wet loose avalanches on sun-exposed slopes. Move to shaded or lower angled terrain if you notice snow surfaces becoming wet and weak. When on open wind-exposed terrain, steer around wind drifts and pillowed features on slopes 35 degrees and steeper.

Summary

Discussion

On Sunday an observers reported small loose wet avalanches on steep east slopes and an intentionally triggered wind slab avalanche in cross-loaded, wind-exposed terrain below treeline near henry creek. 

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. 

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. 

An active weekend for people and avalanches: 

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. 

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. 

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.

Problems

Loose Wet

An icon showing Loose Wet

Likelihood

likely

Expected Size

1 - 1

As the strong March sun shines throughout the day, wet loose avalanches will become a concern on solar aspects. It may not take much solar radiation to affect the recent low-density snow, and for snow surfaces to become wet and weak. Be especially careful of steep rocky slopes facing south and west. Monitor snow surfaces throughout the day, and keep an eye out for roller balls and pinwheels as signs that wet loose avalanches may soon follow. Move to shaded aspects or lower angle terrain to avoid the problem. 

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.

Wind Slabs

An icon showing Wind Slabs

Likelihood

possible

Expected Size

1 - 1

Strong easterly winds redistributed the 4-6in of low-density storm snow from Friday and Saturday into shallow wind slabs at upper elevations. Wind slabs will grow larger and easier to find as you climb up in elevation, and may not be well bonded to a variety of older, slick snow surfaces. Be especially careful if you venture to the eastern portion of the zone (Rock Mountain, White Pine, Chiwaukum Range) where you may be able to trigger deeper avalanches with conditions more similar to the East Central zone. Use small, inconsequential test slopes to check how wind drifts react to your weight. You can also use your pole or quick hand pits to check how slabs are bonding to older snow surfaces. Take time to identify and avoid steep slopes with smooth pillow-like drifts, areas below cornices, or where you find firm hollow snow. Be especially careful around the lee sides of ridges and exposed mid-slope features. In areas sheltered from the wind, new snow may be cohesionless, and loose dry avalanches could occur, running far and fast on steep slopes. Ease into terrain slowly and dial back your terrain selection if you observe recent avalanches, shooting cracks, or whumphing collapses.

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.

Valid until: Mar 16th, 2020 11:10AM

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