Hatcher Pass
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The Bottom Line
Human triggering wind slabs (winds 2/18-21) on leeward aspects, West to North, at upper elevations, may be possible today. With limited data from a week of stormy weather, it will be prudent to thoroughly assess this hazard before stepping it up in steep terrain at the upper elevations.
Persistent slabs continue to linger and will be possible to human trigger at mid to upper elevations. Avalanches will be larger on West to North aspects, 2-5 feet deep, where the persistent weak layers are buried deeper. Remotely triggering avalanches may be possible in isolated locations.
Loose dry avalanches, up to a foot deep, will be possible to trigger in wind protected areas, and on West to North aspects, at all elevations, on slopes 40° and steeper.
Cornices at upper elevations are large and potentially unstable. Any cornice failure may trigger other avalanche problems compounding the risk.
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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. |
Due to stormy conditions Sunday through Wednesday, limited information is available for observed avalanches this week. Cracking and collapsing were observed at low elevation during those days. New snow and wind likely obscured evidence of avalanches. We believe that human triggered and natural avalanches were possible on 2/17-2/19 with new snow and wind. However, it appears that the storm snow bonded better than anticipated. No natural avalanche evidence was observed at any elevation on Friday, also a marginal visibility day.
On Friday, only one test slope, NW, 4000′, 35deg, produced an small skier cut avalanche, 4″ deep x 10 feet wide x 20 feet vertical run, failing within the storm snow.
Storm tracking is as follows:
2/17 7″ new snow with winds SE G23-50 mhp
2/18 5″ new snow with low winds
2/19 7″ new snow
2/19- 2/20 winds increase SE G20-25 mph
2/21 Winds gusted SE 17-25 mph for 9 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 |
SE wind gusts reached a max of 78 mph on 2/18, and gusts were SE/E 35-79 mph from 2/18-2/20, with additional wind gusting SE 17-25 for 9 hours on 2/21. These strong winds have formed wind slabs which may be possible to human trigger up to D2 in size, in specific leeward locations, at upper elevations on West to North aspects, on slopes above 35º today. Wind slabs are estimated to be up to 12″/30cm thick. Natural avalanches will be unlikely today.
Cracking and collapsing are red flags for this problem. Probe testing is a good way to identify the presence of wind slabs, revealing firmer, strong snow, sitting over softer, weaker snow. Expect any firm wind slabs to have the potential for breaking well above you, making escape difficult.
The wind slab problem should be short lived and heal within the next few days.
| 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 |
It will be difficult to predict exactly where triggering a persistent slab will be possible. In isolated locations, it may be possible to remotely trigger an avalanche. You may not observe warning signs, such as collapsing, whumphing or shooting cracks prior to triggering an avalanche.
The persistent slab problem will continue to linger, with natural avalanches unlikely, and human triggered possible at mid to upper elevations on all aspects.
Slab avalanches will be deeper, 2-5 feet deep, on West to North aspects, due to the predominant wind direction and wind loading on these slopes. In other areas the persistent slab is approximately 1-2 feet deep.
It may require numerous people, or a large load, such as a snow machine, to trigger an avalanche. It could just take finding a thin spot in a slab to transfer your weight to the buried weak layer and allow for a failure to propagate a large release.
Last week the persistent slab problem was also stubborn to trigger, but one snow machiner found a low 30’s° slope and triggered a persistent slab, pictured below. This same weak layer problem continues to persist, but is now buried deeper.
2/16 – Craigie Creek, SW, 4000′. Persistent slab avalanche. This same problem will linger through the weekend. In this case the rider was able to traverse off the slab to safety.
| 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 |
At all elevations, and in wind protected areas, generally West to North aspects, approximately a foot of loose snow may be possible to human trigger on slopes 40° and steeper.
Small dry loose avalanches will have the ability to catch and carry a person into terrain traps, compounding the hazard.
With a lot of new snow and strong winds over the last couple of weeks, cornices have grown in size. Large cornices are overhanging and potentially unstable in specific areas at upper elevations, generally, but not limited to, West to North aspects. Natural failures may be possible, but will be very difficult to predict. Human triggering will be possible today.
Be cautious of triggering cornices from above, onto people below. If you are approaching cornices from behind, use extreme caution, gain a safe viewpoint to identify safe entries onto slopes below, and do not step out on overhanging cornice features.
If traveling under cornices, limit your exposure.
Cornice failures may be large, and the mass of a cornice may be large enough to injure or kill a person, or trigger additional avalanche problems.
Here’s what we are seeing in the models for this weekend:
Temps for Saturday at 5000′, 8-11°F cooling to 4-7°F, winds dropping to 0-7 mph, variable direction. Possible trace of new snow today, with a chance for 1-3″ tonight.
Cloudy skies, with the chance for partly cloudy skies today. More clouds this evening and overnight, with a break in the clouds and clearing skies Sunday afternoon and into Monday
Here’s a storm snap-shot of what we saw this week:
2/17 7″ new snow with winds SE G23-50 mhp
2/18 5″ new snow with low winds
2/19 7″ new snow
2/19- 2/20 winds increase SE G20-25 mph
2/21 Winds gusted SE 17-25 mph for 9 hours
NWS Rec Forecast here.
NWS point forecast here.
State Parks Snow Report and Motorized Access information here.
