Hatcher Pass
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The Bottom Line
Today’s primary avalanche concern is Persistent Slab. It will be possible to human trigger small to large persistent slab avalanches on slopes 35º and steeper, where stiff snow overlies old, weak, sugary snow.
This problem will be found predominately near upper elevation ridgelines, on SW to NE aspects, but also exists in a more patchy distribution throughout Hatcher Pass.
We will be increasing our safety margins by spacing out while traveling through avalanche terrain.
A secondary avalanche concern exists for small Loose Dry avalanches which will be easy to human trigger on any slope 40° and steeper.
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| 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. |
Many small natural loose dry avalanches occurred after new snow accumulated on 12/17.
There were two human triggered avalanches reported this week. Both were on the north side of 4068.
12/14 – This avalanche is an outlier avalanche. Occurred where an old glide crack had previously released and fresh soft snow had drifted in. The snowpack was much shallower in this location than other 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 |
This is the classic avalanche problem. A cohesive layer of stiff snow (slab) sits on top of a weaker layer of sugary, poorly bonded snow (weak layer). It is easy to identify IF you dig into the snowpack, otherwise you may not perceive the existence of this problem. Major flaws in the structure of the snowpack can be seen in this video:
New snow over the last 48 hours plus additional new snowfall today is not expected to increase this hazard. This snow has been and is expected to accumulate as low density, light fluffy powder lacking wind. This is an incremental load, not a large rapid load, and the persistent slab has been and is expected to easily adjust.
We expect any avalanche triggered to be small in size based on spatial variability and the lack of slab continuity. However, there are isolated locations where the continuity of slabs may be much more connected, as seen in the wind distribution evidence, and observations from boots on the ground. In these cases a large avalanche will be capable of injuring, burying, or killing a person. Slab thickness varies greatly from 3″ to 15″ on average.
As you look around Hatcher Pass, you will not see much evidence of recent avalanches. One reason for this is a fresh covering of new snow. Visual clues for previous wind loading and drifting will also be disguised by the new snow.
It may be possible to trigger an avalanche from an adjacent location or from below, remotely. Hard slabs may allow for numerous people to travel on a slope before someone triggers it. Tracks on a slope are not an indication of stability.
Pay attention to red flags for this problem. Collapsing, shooting cracks, poor instability test results, and recent avalanches are all examples of the snowpack warning you of danger.
TRAVEL ADVICE: Predicting where and when a person may trigger an avalanche will be extremely difficult even for an expert. Since we don’t have a reliable or highly accurate method for predicting this problems behavior, we will focus on travel techniques to minimize the risk of any avalanche occurrence. We will be spacing out across large slopes, utilizing safe zones for grouping up, and avoiding slopes with terrain traps. We will also be more suspect of this problem on SW to NE aspects at upper elevations and in gaps and passes where previous winds built thicker, larger, and more dangerous slabs.
| 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 |
3″ of new low density snow accumulated December 17th. Several loose dry avalanches failed naturally during and just after the storm. These were small in size. It will be easy to human trigger small loose dry avalanches today on slopes 40º and steeper. Some small natural activity is expected today with additional snowfall.
New snow over the last couple days 5″.
Today we expect 1-4″.
The combination of 12/17, overnight, and today’s new snow will be increasing the potential size and volume of human triggered loose dry avalanches this afternoon and overnight.
While avalanche size will be small, getting caught up in a loose dry avalanche in steep terrain may sweep you into terrain traps compounding the overall hazard.
We will be adjusting our travel protocol to account for this increasing hazard. Loose snow will not bond well to old surfaces, and will be easy to trigger on slopes 40º and steeper.
12/17 – SW, 4500′. Small natural Loose Dry in steep terrain.
