The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is moderate.
Known problems include Persistent Slabs.
The Bottom Line: At upper elevations, avalanches may be deep and unsurvivable. Dangerous conditions exist after another significant storm has added more snow over a very weak layer. Stay off of, and out from underneath slopes steeper than 30 degrees if you see signs of danger like recent avalanches, and shooting cracks.
Summary
Snow and Avalanche Discussion
When digging around for information today, the most common response was "I thought about going out, but the snow quality seemed low." We are in the dark regarding what happened during the storm. We do know that we picked up anywhere from 0.3” to 1.2” of water equivalent, with the Salmon la Sac being the winner. Conditions are likely very dangerous in that area, and as one goes up in elevation.
Mission Ridge and Blewett Pass only picked up a few inches of new snow. A freezing rain crust formed up to about 4500ft across the eastern slopes, with a rain crust likely up to at least 6,000ft. Above 6,000ft the new snow is likely sitting on a recent crop of surface hoar and/or facets, which could make for poor bonding and potentially wide avalanches.
Weather Forecast
Sat 5th Jan 14:52
- Robert Hahn
Weather Synopsis for Saturday night through Monday
An elongated open trough extends southward to the northern California coastal waters. The trough approaches the Pacific Northwest on Saturday afternoon with rain and snow spreading into the Olympic Mountains and southern Washington Cascades Saturday afternoon. This band of rain and snow will lift northward during the evening hours.
Saturday night will feature a wind storm. Strong southerly winds ahead of the rotating trough will be accompanied by moderate to strong easterly flow through the passes. Temperatures will be borderline for snow at Snoqualmie Pass. Once the surface trough passes, the flow will shift westerly and strong westerly winds will buffet the mountains in the early morning hours, bringing sharp cooling. Precipitation will be light to moderate in most locations, becoming snow showers after midnight and continuing Sunday in the unstable cold air behind the trough. Expect 7-14 inches of snow by the end of the day on Sunday for the Cascade volcanoes with the passes and Crystal picking up 2-6".
Light snow showers will continue Sunday night into Monday, mostly confined to the west slopes of the Cascades. Snow levels will remain well below pass level. A ridge building late Monday will generally cut off the moisture from south to north.
Regional Synopsis
Fri 4th Jan 09:00
The first few days of 2019 were active here in the Northwest. A strong weather system impacted the region bringing warm temperatures, heavy precipitation, and strong winds. This weather system did not impact the forecast areas equally. Even within the same forecast zone we can see wide discrepancies in precipitation numbers. The snowpack you encounter this weekend will be largely dependent on where you go and the elevation at which you travel
Storm Precipitation Totals as of Friday Afternoon
Hurricane Ridge: 2.41”
Mt Baker: 6.52”
Stevens Pass: 2.58”
Snoqualmie Pass: 2.27”
Crystal Mountain: 0.52”
Paradise: 2.23”
White Pass: 0.55”
Washington Pass: 1.05”
Mission Ridge: 0.31”
Mt Hood Meadows: 0.51”
A few big stories stand out in the current snowpack: recent avalanche warnings in the northern zones, persistent slabs in the western areas, and a complex and weak snowpack in the eastern zones.
The northern zone experienced the brunt of this latest weather system. This led to two days of avalanche warnings and at least one large natural avalanche cycle. It's tough to say what the snowpack looks like in areas near and above treeline, but we know those areas received substantial new snow.
Photo: Large natural avalanche at Mt Baker Ski Area during the recent storm - Mt Baker Ski Patrol
Earlier in the week we began forecasting a new persistent slab in our west-slope zones. A layer of buried surface hoar produced avalanches last Saturday, Sunday, and Monday. How did that layer fair after this recent round of weather? In locations like Mt Baker and Paradise, it was well tested with heavy precipitation. In other locations, less water may not have adequately stressed the weak layer. As visibility improves and more observation come-in the picture may become more clear.
Large remotely triggered persistent slab avalanche in the Crystal backcountry: Jeremy Allyn
In the eastern zones a complicated and weak snowpack exists. Several persistent weaklayers have plagued these regions most of the winter. Don’t expect this to change anytime soon. Snow profiles and snowpack test can give you a glimpse into the persistent layer. Remember, snow profiles cannot prove the absence of a weak layer or that a layer has “healed.”
Large remotely triggered slide on buried surface hoar from Christmas above Leavenworth on 12/31: Matt Primomo
Problems
Persistent Slabs
On the 31st, I found a highly reactive layer of buried surface hoar down about 18” near Leavenworth. The instability on this layer was found starting at 5,600ft and became ‘in your face’ at 6,400ft. Here, I triggered a number of very wide avalanches while walking on a ridgeline from a distance. A recent avalanche cycle on this layer was observed, but not everything had slid. Activity appeared to be mainly on North through Southeast aspects. These avalanches were surprising in how widely they broke across a slope and the fact that they were triggered from up to 200ft away. Observers in the Washington Pass area also were triggering avalanches on this layer the previous day. On Rock Mountain near Stevens Pass, a very wide crown speaks to the presence of a layer of buried surface hoar. I would be wary of any steep, open slopes above 6,000ft right now, because I would expect these persistent grains to be buried 2 to 3 feet down. From recent experience we know that slides on this layer can be very wide. Snowpack tests can help identify this layer, but cannot prove its absence. Be observant of shooting cracks or collapsing to check for this layer. Use slopes of less than 30 degrees for travel, and avoid getting underneath any steep slopes at upper elevations. At lower elevations, where water has percolated through the snowpack and refrozen to create thick crusts the snowpack is likely bonded much better.
The further east you get, the less snow is on the ground. Recent observations from Mission Ridge and above Mazama the a speak to a shallow snowpack with weak snow near the ground. This poor snowpack structure warrants respect, because if the layer near the ground failed, the avalanche could be well over 4 feet deep. Places to be cautious of in particular are where stiff slabs sit over weak snow, slopes where the ground and rocks may be showing with deep drifts nearby, and any steep slopes on the far eastern side of the range.
