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The avalanche hazard is Moderate at all elevations and on all aspects for Persistent Slab avalanches and Loose Dry.
It will be possible to human trigger large, full depth slab avalanches, generally 2-3 feet deep, that could bury, injure, or kill a person. Natural avalanches are unlikely.
Remotely triggered slab avalanches are especially dangerous, and will be possible. They are difficult to predict or anticipate. It will be possible to trigger avalanches from a long distance away, from adjacent terrain, or from the flats below a steeper slope.
Whumphing and shooting cracks are bulls-eye clues for the persistent slab problem.
While we have received a lot of snow recently and Hatcher is looking like a winterland, the coverage is still quite shallow. Rocks and hazards are lingering just below the snow surface.
The beginning of the season is always a good time to review the North American Avalanche Danger Scale, click HERE for a 2.5 minute informational video.
Welcome to the 2021 season! Our organization depends on your donations to operate. We are currently seeking donors to sponsor forecasts. Please spread the word and contact us here: info@hpavalanche.org
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. |
The last reported avalanche was on 11/10. This human triggered avalanche was reported to be 3 feet deep, 2oo feet wide and ran 40 vertical feet. The rider thinks they may have triggered it from the base of the slope after decent, as it was seen coming down after them. See observations HERE.
On 11/9 numerous natural avalanches were documented after the 11/7-8 storm (Election Dump) which deposited approximately 2 feet of snow over a persistent weak layer formed in October. Click HERE for more photos and information. This weak layer allowed for wide avalanches and crowns that wrapped around terrain features.
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 |
The good news is the avalanche hazard has been slowly improving over time since the last natural avalanche cycle on 11/7-8. Natural avalanches are unlikely.
The bad news is that while it is becoming less likely to trigger an avalanche, it is still possible, and any avalanche triggered will likely be large in size, and able to bury, injure, or kill a person. The persistent slabs problem exists at all elevations and on all aspects.
Additionally, remotely triggered avalanches are possible. Remotely triggered avalanches are very difficult to predict and can be triggered from a long distance away, from the flats below a steeper slope, or in adjacent terrain. Pay close attention to other user groups in your area, as either party could unknowingly endanger the other.
The primary layer of concern is a persistent weak layer of faceted, sugary snow near the ground which was formed in October. This flaw in the snowpack will continue to be a problem with each subsequent loading event. Expect a spike in avalanche activity during and just after significant loading events, and for increasing stability to be slow thereafter.
More details:
The October facet layer was buried and reactive to human triggers after it was overloaded by approximately one foot of snow (at approx. 3000′) on 10/26 (Halloween Storm). Human triggered and remotely triggered avalanches occurred just after the storm. See observations HERE.
After this storm cycle, the avalanche hazard slowly improved, but the weak layer did not go away. And its not going to anytime soon.
The Election Dump on 11/7-8 deposited approximately 24″ of new snow at 3000′. This overloaded the weak layer again which resulted in numerous natural avalanches and lingering instabilities after the storm. More info and pictures in observations HERE.
This is where we are now, 6 days after the Election Dump avalanche cycle, and seeing slow improvement. Note that the last human triggered avalanche was reported 4 days ago on 11/10, which was large in size, and may have been triggered from the base of the slope. This demonstrates the lingering persistence of the current avalanche problem.
Avalanches are more likely on slopes 35° and steeper, and deeper where previous wind loading has drifted snow, either in the mid pack and/or on the surface. A very general rule of thumb is that recent SE winds loaded West to North aspects at mid to upper elevations and these slopes may be more prone to avalanches. This should be taken with a heavy grain of salt, as we have seen the avalanche problem on all aspects.
While winds have loaded leeward slopes, and increased the depth of the snowpack in specific areas, its worth mentioning that no portion of the snowpack is so deep that your weight can not affect the buried weak layers.
In the lower elevations we are keeping the hazard elevated to moderate. Even though there is less snow, the weak layer is present and whumphing has been observed. Our concern here is that you may be able to trigger an avalanche remotely on a steep slope above you. An example would be traveling at the low/mid elevation boundary under marmot mountain. We would have some concern being exposed to large, steep slopes above you, and for the potential to trigger them given the propagation potential of the weak layer. We also think that there may be isolated locations where the wind has stiffened the snow and created a slab capable of an avalanche. It’s still early in the season, we could use more data to increase the forecast certainty.
How we will reduce risk in avalanche terrain this weekend:
We will be playing it safe and choosing conservative terrain choices this weekend. We will avoid slopes with terrain traps in the runnout. We will be choosing lower angle slopes in the mid elevation band that have a grass or tundra base and lack stiff snow overlying weaker snow. We will also be avoiding obvious areas of previous wind loading and drifting where stiffer snow overlies the weak layer. We will be probing the snow to identify this structure and avoid it.
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 |
Loose dry avalanches and sluffing will be possible on steep slopes, 40 degrees and steeper, at mid to upper elevations on all aspects, in wind protected areas. Even a small loose avalanche poses a significant risk with shallowly buried rock hazards.