Hatcher Pass Avalanche Center

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Thu, February 11th, 2021 - 7:00AM
Expires
Fri, February 12th, 2021 - 7:00AM
Forecaster
Jake Kayes
Conditions Summary

Today’s avalanche problems are Wind Slab, Storm Slab and Dry Loose. It will be possible to human trigger small Wind Slabs in specific terrain, at upper elevations, on leeward aspects and cross loaded features, West through Northwest. Small, human triggered storm slabs will be possible at mid and upper elevations on all aspects. Small, Dry Loose avalanches will be possible to human trigger at all elevations, on all aspects, on slopes 40°degrees and steeper. Natural avalanches are unlikely. 

Winds could increase for a short period of time this afternoon, if this occurs expect an increase in hazard today.

Small avalanches can still be dangerous, especially if they sweep you into terrain traps. 

While riding conditions have improved, rocks and other hazards are sitting just below the surface. 

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Thu, February 11th, 2021
Recent Avalanches

There were several human triggered dry loose avalanches this week. There was also several small human triggered slab avalanches this week.

2/07: Hatch Peak south face 4200′ click here for more info.

2/07: Ray Wallace Chutes North 4000′ click here for more info.

2/10: Marmot West 4000′. See wind slab below for more info.

Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    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

Moderate winds from the SE blew for 13 hours on 2/10. These winds have created small wind slabs averaging 3-4” thick and up to 10″, these are located at upper elevations on west through northwest aspects. Wind slabs will be located near ridge tops and cross loaded features. These wind slabs will be small in size and human triggered avalanches will be possible. Natural avalanches are unlikely. 

Shooting cracks are a red flag for this avalanche problem. Smooth drifted snow and firmer snow overlying weak snow will be good indicators that wind slabs are present. Pole tests and hand pits will help you quickly identify this avalanche problem. 

Coverage is still thin in Hatcher Pass and even a small avalanche could sweep you through rocks and cause traumatic injury. We recommend using low risk travel techniques when traveling in or around avalanche terrain. Spread out when ascending slopes, only descend slopes one at a time, and choose safe zones that are out of harm’s way.

Debris from small wind slab on Marmot 4000′ West

Small human triggered wind slab. Marmot 4000′ west southwest

Avalanche Problem 2
  • Storm Slabs
    Storm Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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

On 2/10 4” of new snow fell and in some isolated areas has created a soft Storm Slab. These Storm Slab avalanches will be isolated, small in size, and found at mid and upper elevations and on all aspects. Human triggered avalanches are possible, natural avalanches are unlikely. Look for soft, drifted, pillows of upside down snow. In areas where more cohesive new snow sits over older weaker snow, it may be possible to trigger shooting cracks, and small soft slab releases. Pay particular attention to the south facing, windward aspects. In these locations you will be able to visually identify wind texture, drifting and a “pillowy appearance”. 

SE face of Hatch Peak Light to moderate winds were able to transport low density new snow very short distances, creating this texture and the potential for triggering small, soft slabs in isolated locations. In most cases this snow will lack cohesion and not act as a slab, but we believe there are isolated locations where it will be possible to trigger small soft storm slabs.

Avalanche Problem 3
  • Dry Loose
    Dry Loose
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    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

4” of new snow and cold temperatures have created snow surfaces that are very low density. This low density snow will be capable of producing dry loose avalanches at all elevations on all aspects. This avalanche problem will be found on slopes 40° or steeper. Human triggered avalanches are possible and will be small in size. Natural avalanches are unlikely.

Dry loose avalanches are able to gain mass and speed rapidly, and can entrain old weak sugary snow lower in the snowpack. Practice good sluff management if you choose to venture out into steeper terrain. These avalanches will be small but can catch, carry and sweep you through hazards such as rocks, cliffs and terrain traps if not managed properly. 

 

Weather
Thu, February 11th, 2021

New snow totals Feb 7th -11th:
Independence Mine: 4″ of new snow


The week started out with cold calm winds and temperatures in the single digits and teens. Clear weather, calm winds, and cold temperature have allowed snow surfaces to continue to facet out. South facing slopes are beginning to be affected by the sun, and in some steep areas snow surfaces were going from dry to moist. On Feb 10th 4” of new snow fell at mid and upper elevations, light to moderate winds from the SE were able to transport this snow. As this snow began to fall temperatures began to increase into the mid 20s. 


NWS Rec Forecast here.

NWS point forecast here.

State Parks Snow Report and Motorized Access information here.


Marmot 2/7-11:

 


Independence Mine

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