The Bottom Line: Skyrocketing snow levels to ridge crest by the end of the day, combined with light snow and increasing moderate gusty winds, will create reactive shallow wind slabs. You are most likely to trigger these slabs on wind-loaded slopes or on steeper, convex rolls. A transition to rain may trigger wind slabs or create small loose wet avalanches. Small avalanches are most problematic where they can push you into a terrain trap or into other terrain hazards. Remember, we don't have any specific snowpack observations from the Hurricane Ridge area during the government shutdown, so you will need to account for the extra uncertainty before entering avalanche terrain.
Snow and Avalanche Discussion
The rise in temperatures on Tuesday will be a marked departure from the past several days of cool, quiescent weather which gave older wind slabs a few days to stabilize. As weather changes rapidly, so does the snowpack. Snow doesn't adjust well to rapid change. Continuously monitor the shallow snow above the most recent crust and if you find deeper snow above this crust, retreat to safer, lower-angle, supported terrain.
Friday night's storm brought moderate winds and rising snow levels, but overall Hurricane Ridge saw a net gain of several inches of snow through Saturday afternoon. Rain most likely pushed above 5500', but there was enough new snow and wind along with the cooldown for new wind slabs to have formed in both the near and above treeline elevation bands.
Right now we are forecasting without specific snowpack and avalanche observations from the Hurricane Ridge area due to the government shutdown. If you travel to the Olympic Mountains, please help your local forecast by submitting an observation. We haven’t received updated snowpack information for one month.
Regional Synopsis
January 20, 2019
The recent weather pattern of lower accumulation storms (by NW standards) and longer stretches of calm weather should continue as we move into late January. Since January 17th, incremental snow accumulations punctuated with rising freezing levels favored the south and eastern parts of the region. Storm instabilities have risen with storms and gradually subsided.
A storm slab at Mt Baker.
New Snow Problems
Storms over the past week have brought a range of layers from rain crusts, to heavy moist snow, to stiff drifts, to light dry powder. Some storm days, like the 18-19th, saw reactive, but very short-lived avalanches caused by heavy precipitation and wind. Even the longer-lasting avalanche problems, wind slabs, haven't persisted for more than a few days. Where the recent snow is stressing underlying weak layers, more dangerous avalanche conditions have prevailed.
Surface hoar in the East Central zone
Old Snow Problems
Persistent weak layers (PWLs) have been a constant in the eastern zones of the Cascades this winter. As usual, they have been much less problematic at the Passes and west of the Cascade Crest. The latest PWL is a layer of surface hoar, buried around January 17th and found generally east of the Cascade Crest. Buried surface hoar is an active weak layer in the eastern zones and can be found to a limited extent on the eastern edge of the Stevens and Snoqualmie Pass zones. There few, if any, avalanches have been reported on the buried surface hoar. It may be most problematic in open, wind-sheltered terrain, especially well above the valley floor.
You are most likely to find other layers of old weak snow the further you move east from the Cascade crest. Here snowpacks are shallower, more variable, and generally weaker. In some locations, weak snow near the ground can still be found. These basal facets have hung around all season. Digging profiles and using snowpack tests is the best way to gain information about these old persistent weak layers. However, snowpack tests are just one piece of the puzzle. Your terrain decisions shouldn't hinge on any given test result. Because of the size of our forecast zones and the variability in the snowpack, it's important to make snow observations as you travel. We’ll keep watching these old layers, but let us know what you see while you are in the mountains.
