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Heads up! the pattern has shifted.
Human triggered avalanches are likely today, natural avalanches are possible! Remote triggering will be possible.
Today’s avalanche problems: Fresh Wind Slabs up to 2 feet thick and Persistent Slabs 2-4 feet deep.
It will be possible for wind slabs to step down into the deeper, persistent slab problem, failing at or near the ground.
The avalanche hazard will continue to remain elevated with strong winds and new snow through Wednesday.
Travel Advice | Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. | Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. | Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential. | Very dangerous avalanche conditions. Travel in avalanche terrain not recommended. | Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain. |
Likelihood of Avalanches | Natural and human-triggered avalanches unlikely. | Natural avalanches unlikely; human-triggered avalanches possible. | Natural avalanches possible; human-triggered avalanches likely. | Natural avalanches likely; human-triggered avalanches very likely. | Natural and human-triggered avalanches certain. |
Avalanche Size and Distribution | Small avalanches in isolated areas or extreme terrain. | Small avalanches in specific areas; or large avalanches in isolated areas. | Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas. | Large avalanches in many areas; or very large avalanches in specific areas. | Very large avalanches in many areas. |
Signal Word | Size (D scale) | Simple Descriptor |
Small | 1 | Unlikely to bury a person |
Large | 2 | Can bury a person |
Very Large | 3 | Can destroy a house |
Historic | 4 & 5 | Can destroy part or all of a village |
Sensitive wind slabs have formed over the last 24 hours. Shooting cracks, whumphing, active wind loading, and recent avalanches are all red flags for this avalanche problem.
Moderate to strong ESE/SE winds with gusts 30-50mph over the last 12 hours have transported approximately a foot of low density snow (12/19-22) and built wind slabs up to 2 feet thick on leeward aspects, West to North aspects.
These slabs will fail in both the new snow and on persistent grains. Human triggered wind slab avalanches will be likely and natural avalanches will be possible on leeward aspects at mid to upper elevations. At low elevation human triggered wind slabs will be possible and natural avalanches will be unlikely. Remote triggers will be possible where these slabs sit on persistent grains.
Yesterday on a Northwest aspect, at 3000′, on a 35° slope, a backcountry traveler remotely triggered this freshly formed wind slab, likely failing on persistent grains, while digging a test pit. Today these slabs will be twice as deep:
It will be possible for wind slabs to step down into the deeper persistent slab problem, increasing the size and danger of triggering any avalanche. These avalanches will fail at or near the ground, be full depth, up to 2-4 feet deep.
Marmot Weather Station Last 24 hours:
Signal Word | Size (D scale) | Simple Descriptor |
Small | 1 | Unlikely to bury a person |
Large | 2 | Can bury a person |
Very Large | 3 | Can destroy a house |
Historic | 4 & 5 | Can destroy part or all of a village |
Heads up! The pattern has shifted. Shooting cracks, whumphing, active wind loading, and recent avalanches are all red flags for this avalanche problem.
A foot of new snow since 12/19, plus strong winds in the last 24 hours will have overloaded the persistent slab problem on leeward aspects, West to North.
As winds and new snow continue through today and into Wednesday, expect persistent slabs to be likely to human trigger and for natural avalanches to be possible at mid to upper elevations, on all aspects, but more problematic on freshly loaded West to North aspects. At low elevation, on all aspects, expect persistent slabs to be possible to human triggered and natural avalanches to be unlikely.
Remotely triggered avalanches will be possible.
Persistent slabs could reach depths of 2-4 feet deep.
Stack the deck in your favor: The persistent slab will be difficult to predict. Use safe travel protocol and choose slopes without terrain traps.