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Archived

Avalanche Forecast

Jan 10th, 2019–Jan 11th, 2019
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Cascades - East.

The Bottom Line: The avalanche danger is slowly dropping, but the hefty new load of snow is still a concern. You may trigger avalanches in areas where the wind has formed firm slabs or in locations where weak old snow layers exist. You can stay safe by avoiding slopes greater than 35 degrees.

Snow and Avalanche Discussion

The recent upslope storm revived winter in the lowlands of the eastern slopes. It also added a hefty load to the upper elevation snowpack in some places. Snowfall totals appear to vary widely, from 5" to 14", likely more at higher elevations. The snow came in cold and warmed up as it fell, creating a density inversion that may still be noticeable. A common structure to be found out there will be storm snow (with or without a wind slab) over a crust. On the 10th, avalanche workers were able to trigger a number of wind slab avalanches in closed areas at Mission Ridge with explosives. These were from 6" to 16" deep and from 60' to 125' wide, running on the crust. One of these broke into older, weak snow near the ground. This one was on a Northwest aspect at 6300ft. 

Avalanche Problems

Wind Slabs

Recent winds formed slabs in some unusual locations like well below ridgelines, on the sides of gullies, and in places that are normally scoured. Other places have no wind slab whatsoever. Though you may not see the wind actively loading slopes anymore, the slabs that were built the past few days may take a bit longer than normal to heal. These slabs are resting on lower density snow and sitting over a stout crust, a perfect recipe for avalanches. You will need to use your eyes and sense of touch to locate these dangerous areas as you travel. Feel the snow under you as you travel. Does it feel more firm in one location than another? Does it seem hollow? If you see or feel any of these observations, slabs may be nearby. You can stay safe by traveling on ridges,  scoured areas, and any slope less than 35 degrees.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 2 - 2

Persistent Slabs

This snow and wind loading event has stressed older weak layers in some locations. We have a high amount of unertainty regarding how these persistent layers are responding to the new load. What we do know is we have a weak snowpack structure in some locations and we just put more snow on top of it. Persistent slabs can be difficult to assess and predict. If you see any obvious signs of avalanche danger like recent avalanches, cracks in the snow, or feel sudden collapses, stay away from all slopes greater than 30 degrees.

There are two primary layers of concern in the snowpack. You may encounter one or both depending on where you travel. You are most like to encounter persistent slab at higher elevations and in areas towards the eastern edge of the forecast zone.

A layer of buried surface hoar may be found 1-3 ft below the snow surface. This layer is mainly a concern above 6000ft. Above 7,000ft we have virtually no observations, but would be most suspect of this layer up there. 

A layer of weak sugary facets can be found near the ground, particularly in the eastern areas of the forecast zone. If an avalanche failed on this layer, it could be more than 4 feet deep. Use caution if you are traveling in areas where the snowpack is thinner.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 3 - 3

Loose Wet

If the sun breaks out, expect loose wet avalanches to become common. Steep slopes that face the sun are the most likely places these will happen. If you see roller balls or small loose slides that begin entraining snow, get off of steep slopes. These may pack a punch tomorrow.

Aspects: South East, South, South West.

Elevations: All elevations.

Likelihood: Possible

Expected Size: 1 - 1