Avalanche Forecast
Jan 11th, 2019–Jan 12th, 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
2:
Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2:
Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1:
Low
The avalanche danger rating below treeline will be low
Regions: Cascades - East.
The Bottom Line: You may be able to trigger life threatening avalanches in areas where weak old snow exists. The wind has formed firm slabs in some locations that are difficult to trigger, but still present danger. You can stay safe by avoiding slopes greater than 30 degrees.
Snow and Avalanche Discussion
With good weather in store for the weekend, it is likely that folks will be getting up high into the mountains. It is important to realize that there is much uncertainty with our persistent weak layers above 6,000ft, and a high amount of variability within the zone. The recent upslope storm revived winter on the eastern slopes and added a hefty load to the upper elevation snowpack. Snowfall totals vary widely, from 5" to 14", with more at higher elevations. A common structure to be found out there will be storm snow (with or without a wind slab) over a crust. Recent wind slab avalanches at Mission Ridge were from 6" to 16" deep and from 60' to 125' wide, running on this crust. One that started on a Northwest aspect at 6300ft broke into older, weak snow near the ground. At low elevations and on southerly aspects, the snow surface has a thin crust from light rain or sun, and a number of loose wet avalanches were observed.
Avalanche Problems
Persistent Slabs
We are entering the timeframe where obvious clues to avalanche danger like cracks in the snow, or sudden collapses may not be observed. This is why persistent slabs are difficult to assess and predict. We do know that we have a weak snowpack structure in some locations and there is plenty of snow over these layers to act as a slab. The snowpack is slowly adjusting to the new load, but rapidly rising freezing levels and the sun are something to consider. It may influence the reactivity of these slabs. In any case, slides on these deeper weak layers could be very large and life threatening. You can choose to avoid high consequence terrain by staying 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 likely to encounter persistent slabs 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 and where the crust from January 3rd is nonexistent. Above 7,000ft we have virtually no observations. Be suspicious of this layer up there. Recorded avalanches have been on North through Southeast aspects.
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
Wind Slabs
It has been a few days since the wind has actively loaded the slopes, and the slabs that were built the past few days are becoming more stubborn to initiate. They are quite thick, however, and may still make large avalanches. The recent winds formed slabs in some unusual locations like well below ridgelines, on the sides of gullies, and in places that are often scoured. Some locations have no wind slab at all. Where slabs are found, they may be resting over lower density snow and sitting on a crust, an ideal recipe for avalanches. Approach any steep slopes with caution, and be especially careful of steep, unsupported slopes. Use your eyes and sense of touch to locate areas of wind slab as you travel. Does it feel more firm in one location than another? Does it seem hollow? You can stay safe by traveling on ridges, scoured areas, and low angle slopes.
With warming temperatures and sun poking through the fog, loose wet avalanches may 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 on any aspect, get off of steep slopes.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 2 - 2