Avalanche Forecast
Jan 2nd, 2019–Jan 3rd, 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
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: Mt Hood.
The bottom line: Strong winds may redistribute available snow and build new wind slabs in higher elevations, especially below ridges. Use extra caution and avoid steep open slopes where evidence of wind loading has or is occurring.
Avalanche and Snowpack Discussion
Following rain and freezing rain Saturday, 10-12 inches of snow accumulated Saturday night and Sunday with strong WNW winds. Winds shifted to easterly and transported snow to a variety of aspects making wind slabs possible on all aspects. 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 treeline. 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
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.
Weather Forecast
Weather Synopsis for Thursday night through Saturday
After raining cats and dogs at most sites along the west slopes of the Cascades this morning, a plume of warm frontal moisture has lifted north this afternoon, providing a break for the south Washington Cascades. However, the heavier precipitation and stronger winds will stay focused on the Olympics and Mt. Baker area through this evening.
The associated frontal boundary will pass from north to south through the Cascades tonight and precipitation rates will pick up once again. Snow levels will be slow to cool, but a brief period of easterly flow may allow snow levels to briefly drop to Pass level early Friday morning. Once the front passes through, snow levels will settle rather uniformly across the region in the 4000-4500 ft range.
On Friday, the front will split apart as the parent low pressure system stalls off the central B.C. coast and a new upper low digs off the California coast. Post frontal SW flow should mainly benefit the Mt. Baker area in the way of significant accumulating snow showers above 4000 ft. Other areas will see light showers Friday.
Showers should end Friday night with dry conditions forecast through Saturday morning. An approaching longwave trough will begin to shift showers into the Olympics and south Washington Cascades and Mt. Hood on Saturday afternoon.
Avalanche Problems
Wind Slabs
Older wind slabs formed over the weekend are gaining strength. However, strong winds expected Thursday should build new areas of wind slab in higher terrain. You may still trigger wind slabs on convex rollovers, near the sides of cross-loaded gullies, and on newly wind drifted snow below ridgeline. These wind slabs have formed over a very strong freezing rain crust formed last Saturday to at least 7300 ft.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 3 - 3