The Bottom Line: The avalanche danger changes drastically with elevation. The higher the elevation, the higher the risk of triggering an avalanche because there is more new snow, and more wind up there.
Snow and Avalanche Discussion:
The storm ended on the 4th with over 2.5†of water equivalent. Unfortunately much of the precipitation fell as rain up to at least 5,900ft. About 6†of new snow was observed on Friday over a wet snow layer. A handful of loose wet avalanches were observed to have run recently off the Southeast side of Lichtenburg Mountain. Some of these gauged into older snow with debris piles fanning out widely.
Regional Synopsis
20191204 Regional Synopsis 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: 2.41â€
Mt Baker: 6.52â€
Stevens Pass: 2.58â€
Snoqualmie Pass: 2.27â€
Crystal Mountain: 0.52â€
Paradise: 2.23â€
White Pass: 0.55â€
Washington Pass: 1.05â€
Mission Ridge: 0.31â€
Mt Hood Meadows: 0.51â€
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.
Photo: 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.â€
Photo: Large remotely triggered slide on buried surface hoar from Christmas above Leavenworth on 12/31: Matt Primomo
Avalanche Problems
Wind Slabs
North through East through south aspects may be especially prone to wind slabs. 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.
There is a fair amount of uncertainty for upper elevations, but evidence points towards dangerous persistent slabs. Recent avalanche activity from December 30th appeared to be mainly on Northeast through South aspects at upper elevations. A couple of these avalanches were surprising in how widely they broke across a slope or the fact that they were triggered from a distance. Observers confirmed one of these ran on a crust topped with a layer of small facets on a South aspect in Highlands Bowl. At 6,600ft on Rock Mountain, the very wide crown observed speaks to the presence of a layer of buried surface hoar from Christmas. I would be wary of steep, open slopes above 6,000ft such as Jim Hill, Rock Mountain, Mt. Howard, and The Swath right now, because I would expect this layer to be buried about 2 to 3 feet down. You may use snowpack tests, and be observant of shooting cracks or collapsing to check for persistent grain types. Use slopes of less than 30 degrees for travel, and be cautious of going underneath any steep slopes at upper elevations.
