Hatcher Pass
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The Bottom Line
The avalanche hazard is CONSIDERABLE today for Persistent Slabs on all aspects at the mid and upper elevations in specific areas. At the lower elevations, the Persistent Slab avalanche hazard is rated Moderate.
Remotely triggered avalanches will also be possible. This type of trigger is extremely difficult to predict.
Loose Dry avalanches will be likely to trigger at all elevations and on all aspects on slopes 40° and steeper.
Bluebird skies, powder, and the first chance for many to get into the snow for winter recreation this season in the face of dangerous avalanche conditions will be the biggest challenge we face today.
Weak basal sugar snow can fail at or near the ground, releasing the entire snowpack in large, full-depth avalanches.
The snowpack may not give you obvious clues and could easily surprise even the most seasoned backcountry user. Shooting cracks and collapsing may not be present or warn you before triggering an avalanche. Slope scale snowpack assessment will be key today for establishing safe places to recreate. Choose smaller objectives lacking terrain traps.
Since 11/15 Hatcher received 22″ of new low density snow in 2.8″ of snow water equivalent.
Take a moment to study what considerable avalanche hazard is, as many people are confused by this terminology and the actual serious nature of this hazard level.
The Willow Creek Road from Palmer to Independence Mine was plowed yesterday.
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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 large natural avalanches which mostly occurred in the 11/16 cycle pictured below:
11/16 – Pinnacle Slabs, SW, 5200′, Large natural avalanches, high continuity of weak layer and wide propagation
11/16 – Fair Angle connection pass form IM, S, approx. 5000′, Large natural avalanches
11/16 – Microdot, between Standard Run and Swimming Tim’s, S, 4400′, Large natural avalanche
11/16 – Eldorado Bowl, NE, 4000′, Large natural avalanche
11/16 – Eldorado Headwall, E, 4300′, Large natural avalanches
11/16 – Skyscraper, Conditions photo showing previous wind effect
11/16 – Skyscraper, Nixon’s Nose area, SSE, 3800′, Large natural avalanches
11/16 – Large natural avalanche, Marmot, East tilt on broader east face, approx. 4300′
Date? – Arkose ridgeline, large natural avalanche, covered in storm snow
11/16 – Punk Spines, NW, approx. 3800′, Large natural, D2
Date? – Arkose ridgeline, large natural avalanche, covered in storm snow
11/16 – Gold Chord Lake Moraine, SE, 4000′
| 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 |
A persistent weak layer at the base of the snowpack has failed in multiple avalanche cycles this season and continues to be problematic today. This layer is easy to identify with probe tests and in instability tests and is buried up to 1 meter deep.
The hazard is considerable at the mid and upper eleavtions and moderate at the low elevation. This difference is due to a high snow line in the early season. The lower elevations lacks the October faceted weak layer which plagues the mid and upper elevations. With so much new snow this week, we expect human-triggered avalanches to be possible in specific areas at low elevations. Look for clues such as shooting cracks and collapses in the lower elevations.
Triggering this type of avalanche will be large and consequential, certainly able to bury, injure or kill a person.
Travel protocols will be essential today. We will be choosing to travel one at a time and spacing out through avalanche terrain, paying close attention to utilizing safe zones well out of the way of the potential runout of avalanches, avoiding crowded slopes, and be digging test pits to improve the accuracy of our slope scale assessments and go-no-go decision making. Conservative choices will be key today, avoiding the largest and broadest slopes, and avoiding terrain traps.
Red flags:
Since 11/15 Hacther received 22″ of new snow in 3″ of snow water equivalent. This was a significant rapid load on the snowpack that resulted in numerous large natural slab avalanches failing on the basal faceted layer. These avalanches will be visible today and should serve as a reminder to the size and depth of the existing problem.
Winds on 11/9 scoured and loaded specific slopes throughout Hatcher Pass, laying down stiffer snow over weak snow. The pattern of distribution is highly variable. In many cases, visual clues are evident, including scalloping. See the picture of Skyscraper conditions photo for an example. The max gust at 4500′ at this time was 49mph (see picture below). More recently on 11/15 with a max gust of 33mph at 4500′ winds again transported snow, building denser slabs and overloading slopes with rapid loading. These denser layers which are visually apparent in many cases, are of real concern since they sit on weak basal facets, now an upside-sown snowpack, the perfect recipe for an avalanche.
In some areas that were wind-sheltered, the snowpack is almost entirely fist hard low-density snow, and right side up. These locations may be tricky to find, but will be safer locations to recreate in today
Yesterday forecasters were able to get into the field after a challenging week in stormy weather with poor visibility. We again found poor structure and propagation in the basal facet layer in compression tests, extended column tests, and propagation saw tests.
Marmot weather station, 4500′
| 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 |
So much new snow!
With 22″ since 11/15, loose dry avalanches will be easy to trigger on slopes 40º and steeper. Sluffs may be able to sweep you off your feet into or over other rocks and hazards. Sluffs are expected to be medium in volume and speed.
11/17 – Skyscraper Mountain, natural loose dry avalanches
