Avalanche Forecast
Jan 1st, 2019–Jan 2nd, 2019
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
Alpine
3:
Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3:
Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2:
Moderate
The avalanche danger rating below treeline will be moderate
Regions: Cascades - West.
The Bottom Line: You can trigger an avalanche on wind-loaded slopes near and above treeline. A weak layer of buried surface hoar still lingers above 4500ft. Any avalanche triggered on this layer could break widely across terrain features.
Snowpack and Avalanche Discussion
Several natural and human-triggered avalanches were reported in neighboring forecast zones over the past 2 days. These avalanches failed in unusual ways on a layer of buried surface hoar. These avalanches had very wide propagation, shallow crowns, and some even failed mid-slope.
Regional Synopsis
Happy New Year!
Thanks to all of you who volunteer, send observations, and support NWAC in various ways - we appreciate it.
December of 2018 was fun (from a forecasting perspective) with three pronounced avalanche cycles, a couple different persistent weak layers, some rain events, and a flurry of human-triggered avalanches to ring in the New Year. Most importantly, it seems that we made it through the last days of 2018 without anyone getting seriously hurt by an avalanche.
The deep (Dec 9) layer responsible for many of the avalanches early in the month no longer seems to be a problem in the western zones. That said, it is still possible to trigger an avalanche on its counterpart (or basal facets) in the eastern areas.
A widespread layer of surface hoar formed around Christmas. Late December storms preserved this layer in areas above the rain line and we have numerous (more than a dozen) reports of people triggering avalanches on it in the last three days. At least 4 people were caught and carried during this period, but so far we have no reports of serious injury. Most of these avalanches were soft slabs, D1-D2+, but there were several harder wind slabs in the mix.
It appears that the layer is most reactive and/or prevalent in the Crystal Mountain backcountry and in the mountains around Leavenworth and west of Mazama.
Surface Hoar can be an especially tricky and persistent weak layer. Read more about it here.
Avalanche Problems
Wind Slabs
It is possible to trigger wind slabs on lee slopes and terrain features. Wind slabs are gaining strength but still need additional time to heal in specific areas near and above treeline. Be especially careful of convex rollovers, cross-loaded gullies, and wind loaded slopes just below ridgelines. In some areas, wind drifted snow may sit over a layer of buried surface hoar making a recipe for a surprising avalanche that could propagate widely.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 2 - 2
Persistent Slabs
A layer of buried surface hoar has been the culprit in many recent avalanches throughout the region. In neighboring areas, this layer exists 1-2ft below the surface between 4500-6500ft. Recent observations indicate the surface hoar has a spotty distribution and can be hard to find. Regardless, impressive and unusual recent avalanches still have us concerned. Be especially mindful of steep slopes near treeline that are sheltered from the wind and that stayed above the rain during the recent storm. This is a good time to break out the shovel and dig. Look for a thin grey line and/or snowpack tests that fail suddenly in the upper snowpack. If you find the buried surface hoar intact, experience collapses, shooting cracks, or see recent avalanches, stick to lower angled terrain.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 2 - 2