Hatcher Pass Avalanche Center
Hatcher Pass

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Issued
Sat, December 25th, 2021 - 7:00AM
Expires
Sun, December 26th, 2021 - 7:00AM
Forecaster
Allie Barker
Avalanche risk The Bottom Line

Merry Christmas and Happy Holidays!

Small to large PERSISTENT SLABS will be LIKELY to HUMAN TRIGGER at all elevations, on all aspects, on slopes steeper than 30°. Naturals are unlikely.

Unfortunately the snowpack has been ravaged by Thursday’s wind leaving few locations with undisturbed powder.

On Friday, three separate parties in the backcountry triggered avalanches, two were caught and carried, no injuries.

Looking forward: Sunday’s weather forecast predicts significant snow above 3500′ and rain below, both will increase the avalanche hazard.
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HPAC is currently seeking a sponsor for our new web cam. This is a great advertising opportunity. Contact us: andydennis@hpavalanche.org

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Stay tuned for upcoming Forecaster Chats at the Hatcher Pass Lodge on Thursdays.

Sat, December 25th, 2021
Upper Elevation
Above 3,500'
3 - Considerable
Avalanche risk
Mid Elevation
2,500'-3,500'
3 - Considerable
Avalanche risk
Low Elevation
Below 2,500'
3 - Considerable
Avalanche risk
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
Avalanche risk Avalanche risk Avalanche risk Avalanche risk Avalanche risk
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.
Recent Avalanches

Numerous natural, human triggered, remote and sympathetic avalanches occurred Monday through Wednesday. Natural wind slabs were observed on Thur/Friday as a result of Thursdays wind.

Three D1-D2 human triggered and one moose triggered persistent slab occurred on Friday. Two people took a ride in two separate avalanches on Friday, no injuries.

Human triggered slab 12/23 , Lower Microdot W 3700′

 

D1.5 Human triggered persistent slab 12/24 Lower Eldo E 4200′

 

Same avalanche as pic above. 2-3′ deep crown

 

D1.5 Human triggered persistent slab , near Gold Chord Lake 12/24 SW 3800′

 

Same avalanche as picture above, near Gold Chord Lake exit

Naturals on Skyscraper, SE 4200′ 12/23

 

Moose triggered? Persistent slab, SE 2700′ 12/24

Sunnyside of Hatch , Naturals SE 3500′ 12/24

Avalanche Problem 1
  • Persistent Slabs
    Persistent Slabs
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
Likelihood of Avalanches
Terms such as "unlikely", "likely", and "certain" are used to define the scale, with the chance of triggering or observing avalanches increasing as we move up the scale. For our purposes, "Unlikely" means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. "Certain" means that humans will be able to trigger avalanches on many slopes, and natural avalanches are expected.
Size of Avalanches
Avalanche size is defined by the largest potential avalanche, or expected range of sizes related to the problem in question. Assigned size is a qualitative estimate based on the destructive classification system and requires specialists to estimate the harm avalanches may cause to hypothetical objects located in the avalanche track (AAA 2016, CAA 2014). Under this schema, "Small" avalanches are not large enough to bury humans and are relatively harmless unless they carry people over cliffs or through trees or rocks. Moving up the scale, avalanches become "Large" enough to bury, injure, or kill people. "Very Large" avalanches may bury or destroy vehicles or houses, and "Historic" avalanches are massive events capable of altering the landscape.

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
More info at Avalanche.org

It will be LIKELY to HUMAN TRIGGER PERSISTENT SLABS  today on all aspects, at all elevations, on slopes steeper than 30º. Natural avalanches are unlikely.  Avalanches will vary from SMALL to LARGE in size.

As mentioned in Thursday’s forecast, we currently have a textbook set up for persistent slab avalanches. Weak sugary facets from a cold November are widespread and buried under 1-2 feet of snow by previous storms and wind events. Thursdays strong wind event gusted 37mph (or stronger), transporting low density snow, adding stress to the already weak snowpack once again.

In addition to larger terrain, it will be possible to trigger an avalanche in smaller terrain we usually do not focus on such as the road run, fishhook creek gully side walls or the slope above the sledding hill. Much of this terrain funnels into terrain traps which will compound the risk of an avalanche.

Few people ski-toured the backcountry on Friday. All three parties triggered avalanches. Two people were caught and carried with no injuries.

Persistent slabs can be challenging to assess, manage, and avoid.  Recognizing stiff snow overlying weak sugary snow will help to identify this avalanche problem. Ski cutting is not an effective tool for managing slabs sitting on persistent weak layers.

Whumping and shooting cracks, which were widespread and numerous on Friday, continue to be red flags for this avalanche problem. This problem will be slow to heal.

Overcast and snowy conditions this weekend will make it challenging to tell if you are traveling underneath avalanche terrain or remotely trigger an avalanche.

Santa says, If you want to be a good avalanche partner…Space out when ascending slopes, descend slopes one at a time, and make sure you regroup in areas that are out of harm’s way. Avoid traveling and riding above terrain traps, which can increase the consequences if you are caught in an avalanche.

 

 

Weather
Sat, December 25th, 2021

NWS AVG Forecast here.

NWS Rec Forecast here.

NWS point forecast here.

State Parks Snow Report and Motorized Access information here.

Observations
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