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
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: Mt Hood.
The bottom line: Wind slabs formed since the weekend have become more difficult to trigger. However, shifting winds have transported snow to a variety of aspects, making terrain choices more difficult. It may still be possible to trigger an avalanche on steeper wind-loaded slopes.
Avalanche and Snowpack Discussion
Following rain and freezing rain Saturday, 10-12 inches of snow accumulated with strong WNW winds Sunday. Mt. Hood Pro-patrol found fresh but stubborn wind slabs up to 2' deep near treeline. More importantly, wind slabs had developed on unusual aspects, cross-loaded slopes and formed on open slopes below ridges. Winds had scoured ridges to the most recent firm icy crust in many areas. We have no recent observations from above treeline due to the recent stormy conditions.
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.
Regional Synopsis
Weather Synopsis for Wednesday night through Friday
A Pacific front will spread increasing light precipitation to the Olympics and Mt Baker area Wednesday afternoon. The initial warm frontal moisture will be directed mainly across the north part of the forecast area overnight Wednesday. The heaviest precipitation will remain directed to the Mt Baker area Wednesday night, where it should become heavy.
Freezing levels rise rapidly overnight through early Thursday and peak Thursday morning along with continued heavy precipitation in the Mt Baker area with significantly less precipitation reaching the southern WA Cascades and Mt Hood area.
Thursday should be a very wet day, especially in the north part with little to no precipitation reaching the Mt Hood area.
Light easterly winds across the passes are not expected to save the Stevens and Snoqualmie areas from rain, as they often do throughout the winter.
The associated cold front finally crosses the Cascade crest Thursday night, maintaining moderate to heavy precipitation and extending precipitation to the remainder of the forecast area in the south.
Showers should continue to lowering freezing levels Friday as a weak upper trough passes the area. The Mt Baker area will continue to receive the greatest precipitation Friday, with gradually less towards the south.
Avalanche Problems
Wind Slabs
Wind slabs formed over the weekend are gaining strength, but have not fully healed. Backcountry travelers and local professionals reported finding wind slabs in unusual locations such as low on the slope and in areas often wind-stripped. You may still trigger wind slabs on convex rollovers, near the sides of cross-loaded gullies, and on wind drifted snow below ridgelines.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 2 - 2