|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.
No new avalanches were observed on 12/1/23.
A few recent avalanches were observed on 11/29 including those seen below in Rae Wallace D1.5-2.
The 11/29 wind event was strong and transported available low-density snow, overloading a basal weak layer and also producing some avalanches on storm snow interfaces. Wind slabs were active during and just after the wind event on 11/29, however, since then, they have bonded well to precipitaion particles which they sit on. Therefore, wind slabs have been removed from the avalanche problem list since the last forecast.
Recent widespread winds have sculpted the snow surface with sastrugi, scalloping, and breakable wind crusts. Locations with soft powdery snow are few.
|Size (D scale)
|Unlikely to bury a person
|Can bury a person
|Can destroy a house
|4 & 5
|Can destroy part or all of a village
The basal persistent weak layer near the ground consists of old, unconsolidated sugary snow from October. This layer has plagued Hatcher Pass this season and is the main culprit in most avalanches so far. The good news is we are seeing a trend towards better stability. The bad news is avalanches up to 3 feet thick continue to be possible and stubborn to trigger on all aspects at mid and upper elevations on slopes 35º and steeper. Natural avalanches are unlikely.
The upper elevations present the greatest hazard, where temperatures have been colder and the basal persistent weak layer is better preserved. In the mid-elevations, we have seen significant improvements in the stability of the snowpack, but can not remove the possibility of triggering large avalanches here yet.
Snowpack depth varies, generally thicker depths on the North and Western aspects where prevailing winds have deposited snow throughout the season. The South and East aspects, where prevailing winds have scoured snow throughout the season, are generally shallower. This is a tough conundrum since shallower areas will be easier to human trigger, and locations with deeper snowpacks will be harder to trigger, but larger and more dangerous avalanches will be possible.
This type of problem may allow several people to travel without incident, and then be triggered by the next person on slope. In this scenario, we continue to recommend attention to safe travel protocol. Spread out, only one person on the slope at a time, identify and use safe zones, don’t group up at the base of avalanche terrain. Avoid slopes with terrain traps, and choose slopes with gentle, fanning runouts.
Recent avalanches, whumphing, collapsing, and shooting cracks are red flags for this problem.
Previous warmth, moisture, and rain allowed basal facets to round and increase in stability. Observations to up to 4500′ have verified increased stability, but propagation and therefore human triggered avalanche potential still lingers. We have not gone above 4500′ in observations this season. Any avalanche triggered could fail at the ground, releasing the entire snowpack, resulting in a large avalanche capable of injuring, burying, or killing a person. The snowpack is thicker on W to N aspects (clockwise) and therefore any avalanche failing on the basal layer in these areas will be larger in size.