Hatcher Pass Avalanche Center

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Thu, February 18th, 2021 - 7:00AM
Expires
Fri, February 19th, 2021 - 7:00AM
Forecaster
HPAC Staff
Conditions Summary

Today’s avalanche problems will be Wind 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, on West through North aspects. Small Dry loose avalanches will be possible to human trigger at all elevations, and on all aspects, on slopes 40° degrees and steeper. Natural avalanches are unlikely.

Riding conditions have improved but coverage is still thin, especially near ridgetops.

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Thu, February 18th, 2021
Recent Avalanches

Peak 4068 NE: A small natural wind slab was reported.

Marmot 4000’ SW face: a small natural wind slab was reported.

Pictured below: Marmot Mid Rib 3800’ W/NW Aspect: A small, sensitive, human triggered wind slab was observed up to 80’ in width in a cross loaded gully.

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 with strong gusts from the SE blew for 6 hours on 2/17. These winds have created small wind slabs in specific areas with slabs averaging 1-8” thick and in very isolated locations up to 1 foot thick. These are located at the mid and upper elevations on west thru north aspects. These wind slabs will be small in size and possible to human trigger today. Natural avalanches are unlikely. We expect the wind slab problem to improve over the next 24 hours.

Shooting cracks are a red flag for Wind Slabs. Look for smooth freshly drifted snow overlying weak snow when trying to identify this avalanche problem. Pole tests and hand pits will help you quickly identify this avalanche problem

Even a small avalanche could sweep you through rocks or other hazards and cause injuries. Use safe travel techniques when traveling in or around avalanche terrain. We recommend spreading out when ascending slopes, descend slopes one at a time, and choose safe zones that are out of harm’s way.

 

Marmot W 3900′ signs of snow being transported by wind.

 

Flagging and blowing snow on the north face of Bennets Ridge

 

The human triggered Marmot wind slab failed on rimmed stellars.

 

Avalanche Problem 2
  • 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

On 2/16 Hatcher Pass received 5-6” of new, low density snow. It will be possible to human trigger small dry loose avalanches in wind protected areas, at all elevations, on all aspects, on slopes 40° or steeper. Natural avalanches are unlikely. 

Overall there is approximately 1-2 feet of soft, newer snow from the last several storms sitting over older, weaker snow, made up of near surface facets. In isolated locations, in steep terrain, it will be possible to trigger all of this new snow, resulting in larger volume dry loose avalanches. 

Winds and warmth have affected the surface of the snow in specific areas, resulting in an upside down snowpack within the top few inches of the snowpack. This has made dry loose avalanches less widespread than they were previous to this last storm.

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 18th, 2021

New snow totals 2/14-17

Independence Mine: 5-6″

Frostbite Bottom: 3-4″


Temperatures started the week in the low teens, with clear sky and sunny weather. As the week progressed a storm system began to move into the forecast zone. As the storm began to move closer to Hatcher Pass on Feb 15th, temperatures began to rise into the mid 20s. Early in the morning on Feb 16th snow began to fall and by the end of the day 5-6” of snow had accumulated. On Feb 17th moderate to strong SE winds were able to transport this new snow and was able to scour ridge tops. The NWS is calling for 2-4″ of new snow today with light and variable winds, and temperatures rising to 28°F at 3000′. A pattern change is starting tonight with colder temperatures dropping into the single digits and teens through the weekend.


Marmot 4500′ Last 24 Hours:


NWS Rec Forecast here.

NWS point forecast here.

State Parks Snow Report and Motorized Access information here.

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