Avalanche Forecast
Jan 3rd, 2019–Jan 4th, 2019
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
3:
Considerable
The avalanche danger rating below treeline will be considerable
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 - East.
The Bottom Line: Dangerous avalanche conditions exist due to strong wind, new snow, and old weak layers well below the surface. Be very cautious on slopes where you find one foot or more of fresh snow with underlying weak layers. If you see obvious signs of danger like recent avalanches, cracks that shoot through the snow, or a dramatic collapse of the snowpack, stay off of slopes steeper than 30 degrees.
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
Use extra caution at upper elevations on leeward, wind-loaded slopes steeper than 35 degrees. Watch for fresh drifts and areas of variable height storm snow as indicators that you could trigger a wind slab avalanche. Steer around thickly pillowed areas and convex rolls where the terrain gets steeper. Use small, inconsequential test slopes to clue you in to how well the new snow is bonded. In some areas of the zone, wind slabs will be your main concern. In areas where you find underlying weak layers, triggering an avalanche in the new snow could result in a much bigger and more dangerous persistent slab avalanche.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 2 - 2
Persistent Slabs
Snow, rain, and wind are putting a new load on an already weak snowpack. While you can trigger avalanches at all elevations, the most dangerous slopes will be near and above treeline where the wind is loading leeward slopes. You can trigger dangerously large and surprising avalanches on slopes over 30 degrees. Avalanches may be more reactive and break wider than you can expect. You can trigger persistent slabs from a significant distance. Put plenty of space between you and any suspect avalanche terrain. Make sure you are well out from under any areas where avalanches could start. Two weak layers of concern are a thin layer of surface hoar buried 1-2 feet below the surface and sugar-like facets near the bottom of the snowpack.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Likely
Expected Size: 2 - 2