Hatcher Pass
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The Bottom Line
Small dry loose will be possible to human-trigger at all elevations, on all aspects on slopes 40º and steeper.
Small wind slabs 2″ to 8″ thick will be possible to human-trigger above 2500′ in specific locations on Southeast to West aspects.
The 12/5-7 storm snow is sitting on a buried rain crust in the middle of the snowpack, and is a new persistent slab problem that will be possible to trigger in isolated locations at mid to upper elevations on all aspects.
Another round of snow is on its way for late Saturday through Monday. This will almost certainly increase the avalanche danger.
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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. |
Some limited natural slab and loose dry avalanche activity occurred during and right after the 12/5-7 storm which brought a rain crust early in the storm and then 18″ to 20″ of new snow with 2.1″ SWE.
Listed here are some natural avalanches that occurred during the storm, see pictures in recent observation by forecaster Allie Barker.
One large natural avalanche occurred during the storm on Marmot SW proper that filled a gulley with debris.
A large natural avalanche occurred on the south side of Skyscraper during the storm which reached the winter trail.
Peak 4068, NE, 3300′ – Small to large storm slab and loose dry avalanche activity that occurred naturally during the 12/5-7 storm. Old tracks from prior to the storm are still visible.
More storm snow avalanches that occurred during the storm near Martin Mine, ESE, 3500′. Debris piles are still visible but crowns have been filled in with new snow.
Marmot , SW, 3900′ – Small human triggered soft slab, likely failed on rain crust on this shallower wind scoured aspect. Thin crown visible, entrained low density new snow.
| 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 |
18-20” of new low density snow is sitting on a fragile rain crust and will be possible to trigger on slopes 40º and steeper. Cold temperatures will continue to allow the surface snow to loose density, adding to this (favorite) avalanche problem.
In some locations dry loose sluffing may be capable of dredging into older snow and building volume. Slope cutting is an effective technique for testing and managing this problem.
| 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 |
Winds were light during the 12/5-7 storm and began to increase late yesterday afternoon. Winds overnight and for the last 16 hours at the marmot weather station (4500′) were Northwesterly 2-4 mph with gusts 6-11 mph which will have slowly built wind slab up to 8″ thick. It will be possible to human-trigger wind slabs on the leeward aspects, generally Southeast to West, at mid to upper elevations and in gaps and passes.
Small, thin wind slabs were slowly building throughout the day on Friday in specific locations mostly near and just below ridgeline. It was difficult to find locations to produce shooting cracks. We were able to produce one, 100 foot long shooting crack in an area with wind affected snow, however, this slab was only a few inches thick. This will not have changed much overnight and through today.
Today’s winds are expected to continue to remain light which should not increase this avalanche hazard substantially. However, if winds pick up to 15+mph and into the 20’s the wind slab avalanche hazard would increase rapidly. A visual clue of strong winds and drifting snow is flagging or pluming at ridgelines.
Stiff snow overlying weaker snow will be easy to identify with pole or probe testing. Shooting cracks are a red flag for this problem. Surface markings will be visually apparent and provide evidence for the location of this problem.
12/9 Skyscraper East conditions photo – Be on the lookout for this kind of wind slab visual clue today. This ridge feature has the classic visual markings of wind slabs and wind effected snow.
| 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 |
Two persistent slabs exist on all aspects and at all elevations. One is the new snow sitting on a crust and the other is the entire snowpack sitting on the basal facets we have been talking about all season.
The newest persistent slab is the 12/5-7 storm snow sitting on a rain crust approximately 12-18” deep. This crust formed by rain at the beginning of the storm, and is now buried under the new snow.
Since the new snow is low density and generally not cohesive enough to act as a slab, there is little concern for triggering this persistent slab in most locations. However, there are isolated locations, such as upper elevation ridgelines and in gaps and passes where wind stiffened snow will be more prevalent and possible to human-trigger. Pole tests and snow surface clues will assist you to identify problem areas. Shooting cracks and collapsing are a red flag for this problem.
If winds pick up and drift snow, this avalanche problem will become larger and more reactive.
The second persistent slab is what we have been talking about all season and is the entire snowpack that has the potential for failing on the basal facets at and near the ground. Stability for this problem has slowly increased over the last two weeks. Human-triggering this problem is unlikely but could occur in isolated locations at all elevations and on all aspects. While some natural avalanches occurred during the recent storm, none of them failed at the ground on this layer. Fortunately, this last round of snow (12/5-7) did not overload the basal weak layer. This hazard could increase if winds pick up, transport snow, and rapidly add a load to the snowpack.
This morning’s NWS Avalanche Weather Guidance discussion is predicting a significant weather event moving into our area late this weekend and into Monday. This will almost certainly increase the avalanche danger.
A combination of a weakening low over the Gulf and high pressure inland will maintain strong and gusty northerly winds this morning, especially through mountain passes and along ridge tops. Winds are expected to diminish from west to east today as high pressure moves overhead. As high pressure slowly moves east, expect increasing cloud cover as a frontal system moves eastward into the western Gulf late this afternoon and into Southcentral tonight. Given the upper level support and deep moisture fetch, forecast confidence is high that this will be a widespread heavy snow event for the mountains beginning late Saturday night or early Sunday morning, and continuing through Monday. Most of the uncertainty is the exact timing of the snow event and where the heaviest amount of snowfall will fall. Overall, this will be an impactful winter storm.
NWS AVG Forecast here.
NWS point forecast here.
Marmot Weather Station here.
Independence Mine Snotel here.
State Parks Snow Report and Motorized Access information here.
