Hatcher Pass Avalanche Center
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Issued
Sat, December 7th, 2019 - 7:00AM
Expires
Sun, December 8th, 2019 - 7:00AM
Forecaster
HPAC Staff
Avalanche risk The Bottom Line

Natural avalanches are unlikely today. New shallow 4-6″ wind slabs that formed overnight will be possible to human trigger on West to North aspects at Upper elevation on slopes above 35º.  Wind slab hazard will increase throughout the day.  Dry-loose avalanches will be possible to human trigger, on all aspects, at mid and upper elevation, on slopes 35º or steeper. Dry-loose avalanches will be capable of dragging or washing you into other, larger hazards, compounding the danger. Expect dry loose to be small in size but capable of burying a person in channeled terrain and terrain traps.  Glides cracks and cornices will be an unpredictable, high consequence hazard this weekend.

Special Announcements

Mark your calendars for our annual HPAC Rescue Workshop @ HP with the HP Snowriders Club, CNFAIC Forecasters, Black Diamond , and more….Saturday, January 11 at the Gold Mint Lot at Hatcher Pass.

See the State Parks Report under the Weather tab for Snowmachine openings and information.

Thank you to everyone who donated during “Giving Tuesday.” We appreciate your support. If you feel left out, you can still GIVE HERE.

Sat, December 7th, 2019
Upper Elevation
Above 3,500'
2 - Moderate
Avalanche risk
Mid Elevation
2,500'-3,500'
2 - Moderate
Avalanche risk
Low Elevation
Below 2,500'
1 - Low
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

No new slab avalanches were observed this week.

New glide cracks were observed on all aspects at mid and upper elevation. Old glides continue to expand.

Dry loose sluffs were observed later in the week, large enough to injure or bury.

A report came in on 12/5 of an unintentional human triggered cornice collapse in Rae Wallace on Marmot Mountain. The 10′ wide X 12′ tall cornice failed under foot, triggering a large, dry loose avalanche that ran to the bottom of the slope. 1 person caught and carried under the snow the entire time, ending up at the bottom of the gully, and able to self-rescue. 1 person caught, carried, self- arrested 200′ down slope.  No known injuries. 12/8 See OBS for more information.

See pics under addition concerns.

Above: Glide on Skyscraper

 

Above: Glide, Point 40 near Microdot, occurred @ 12/2/19

Above: Cornice collapse on Rae Wallace. Cornice fall triggered dry loose, ran to bottom of slope, caught and carried 2 people .12.5.19

 

Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
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

Winds at 4500′ picked up over the past 11 hours, gusting ESE 17-38 forming new winds slabs that will be possible to human trigger, on leeward aspects West to North, on slopes above 35º, at upper elevation. Expect slabs to be 4-6″ thick and increasing in size throughout the day.

Wind slabs may be sitting on buried surface hoar that has been forming over the past several days. Surface hoar was observed to be widespread, 6mm in size, and standing tall previous to wind slab development. This problem is guilty until proven innocent and requires careful assessment.

It will be possible for wind slabs to trigger dry loose, increasing the size and consequence of the avalanche problem. Winds slabs will start off small, and increase in size throughout the day as winds continue. By the end of the day, this hazard may increase to considerable.

 

Avalanche Problem 2
  • Dry Loose
    Dry Loose
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Dry Loose
Dry Loose avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.
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 possible to human trigger dry loose avalanches today at mid and upper elevations, on slopes steeper than 35º, on all aspects. Dry loose avalanches will vary from small to large in size and in some cases large enough to bury a person. Most observations Wednesday and Thursday included humans triggering and/or managing “sluffs”. These backcountry users either managed, outran, were caught, or partially buried in loose dry avalanches. No injuries reported.

Above: Human triggered dry loose sluff on Skyscraper 12/5

 

Above: Dry Loose on Marmot 12/1/19.

Loose dry avalanches have been a hazard this week and will continue through the weekend. We recommend sluff management techniques to avoid either getting caught by your own sluff, or triggering loose dry avalanches on top of other people.

We recommend skiing one at a time, using good safe zones, and radio communication if possible. Ask yourself: Is this really a safe zone? If someone above me triggers an avalanche, could it hit me? Let’s all re-consider what appropriate safe zones look like at HP.

We anticipate this problem to be short-lived as temperatures are forecasted to warm up significantly over the next several days.

 

 

 

Avalanche Problem 3
  • Glide Avalanches
    Glide Avalanches
Glide Avalanches
Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.
More info at Avalanche.org

Glide cracks continue to form, expand, and release unpredictably. The most impressive glide avalanches can be seen on Marmot. See picture here or Observations here.  Avoidance is the best tactic for mitigating this high consequence hazard.

Above: Glides in Eldorado bowl 12/5

 

Above: Glide and old wind slab in Martin Mine. 12/3 ?

 

Additional Concern
  • Cornice
    Cornice
Cornice
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
More info at Avalanche.org

Cornices are large, overhanging, and difficult to asses and predict when they will fail. Give cornices a wide berth. Cornice failures can trigger additional avalanche problems which will compound the hazard. Avoiding cornices can be difficult, as we often approach them from the blind, backside, or from below where they are too far away to properly visually assess.

Picture below: A report came in on 12/5 of an unintentional human triggered cornice collapse in Rae Wallace on Marmot Mountain. The 10′ wide X 12′ tall cornice failed under foot, triggering a large, dry loose avalanche that ran to the bottom of the slope. 1 person caught and carried under the snow the entire time, ending up at the bottom of the gully, and able to self-rescue. 1 person caught, carried, self- arrested 200′ down slope.  No known injuries. 12/8 See OBS for more information.

Above: 10′ X 12′ Cornice collapse on Rae Wallace. Look at how many tracks there are! 12.5.19. Photo: Ben Reynolds

 

Above: Cornice that was human triggered, failed, triggered dry loose, caught and carried 2 people, and ran to the bottom of the slope. 12.5.19 Photo: Ben Reynolds

 

 

Weather
Sat, December 7th, 2019

NWS Rec Forecast here.

NWS point forecast here.

State Parks Snow Report and Motorized Access information here.

This week at Marmot Weather Station 4500′:

Average temp 15ºF, with a high of 25ºF, low of 2ºF

Winds averaged ESE 5 mph, gusting ESE 21 mph. Winds gusted ESE 17-38mph for 10 hours overnight.

This week at IM Snotel 3550′:

Average temperature  18ºF, with a high of  32ºF low of  5ºF.

3-5″ new snow and 4″ SWE.

 

 

Observations
Recent Observations for Hatcher Pass