Next 2 pictures: Two significant avalanches ran on SE side of Marmot Mountain during the Thanksgiving Storm. One in Marmot Gully One and another in Marmot Gully 2, both with debris making it very close to the road. The avalanches appear to have released mid-height in the bowls, mostly on the steeper sidewalls. The main portions of the bowls appear intact. Poor visibility has made identifying the bed surface difficult, but the Veteran’s Day Crust is suspected.
Numerous small storm slab and/or wind slab avalanches were observed in the Rae Wallace north chutes. No pictures available.
Significant new glide cracks have recently formed on the SW face of Marmot:
Storm slabs will be possible to trigger in isolated locations, 1-3 feet deep, at mid to upper elevations. Storm slabs are present on all aspects.
With the lack of any persistent grain types at the new snow/old snow interface, we expect instabilities to be short lived and significant improvement over the next 24 hours. New snow, precipitation, and wind forecasted for today, should not significantly impact stability.
Wind slabs, formed during the Thanksgiving Storm, will still be possible to human trigger today, 1-3 feet deep, located on leeward aspects, on both top loaded ridgelines and cross-loaded slopes and features, generally West to North, at mid to upper elevation. Winds were strong enough to build wind slabs not just at the top of slopes, but also mid-slope.
While West to North aspects have the heaviest wind loads, all aspects were affected by wind. A variety of wind sculpting is widespread, from large drifts to scalloping, to wind board, mixed in with few locations of non-wind effected snow.
Yesterday observers traveling on steep northerly aspects where wind loading was the most significant, found good bonding at the new/old snow interface.
Winds were strong and visibly transporting snow at upper elevation ridgelines yesterday. Winds continued to transport snow overnight and add to the wind slab problem. Overnight winds at 4500′ were SE 10-19 mph, gusting 18-26 mph, and at 3550′ E and SE 1-8 mph, gusting 4-19 mph.
Overall we expect this avalanche problem to be improving substantially today and into tomorrow.
A new glide crack on Marmot Mountain’s SW face is a reminder that this problem is still active. There is a high level of uncertainty with the timing and prediction for glide avalanche release. Avoidance is the best way to mitigate this low frequency/high consequence hazard. Avoid old glide avalanche paths which have the potential to release again. Avoid any area with glide cracks, or “brown frowns”, which can release unexpectedly.
NWS Rec Forecast here.
NWS point forecast here.
State Parks Snow Report and Motorized Access information here.
Strong winds during the Thanksgiving Storm have made it difficult to measure new snow totals, both through weather station measurements and field observations. We are basing our best guess on the snow water equivalent from the Independence Mine Snotel data. A storm total of approximately 3.2″ of SWE roughs out to 30″ of new snow in this storm cycle. This number also seems consistent with our observations at the Marmot snow stake. Adjustments to the stake were made yesterday to account for snowdrifts blocking the view of the stake, see the latest image here.
This week at Marmot Weather Station 4500′:
Average temp 16ºF, with a high of 26ºF, low of 2ºF
Winds averaged SE 10-34 mph, gusting 17-55 mph.
This week at IM Snotel 3550′:
Average temperature 21ºF, with a high of 34ºF low of 3ºF.