Hatcher Pass Avalanche Center

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Thu, February 25th, 2021 - 7:00AM
Expires
Fri, February 26th, 2021 - 7:00AM
Forecaster
Jake Kayes
Conditions Summary

Hatcher Pass has received approximately 7” of new snow this week and an additional 2″ last night. Today’s avalanche problems are Storm Slabs, Winds Slabs and Dry Loose. It will be possible for humans to trigger small storm slabs 7” thick at all elevations on all aspects. Small human triggered Wind Slabs, 3-5” thick will be possible at mid and upper elevations, on West thru North aspects. Natural avalanches are unlikely.

Recent avalanches, shooting cracks and whumping will be red flags for today. Small avalanches can still be dangerous, especially if they sweep you into terrain traps. 

Riding conditions have improved, rocks and other hazards are slowly getting buried deeper. Ridge tops still have shallow conditions.

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Thu, February 25th, 2021
Recent Avalanches

There were two small human triggered Storm Slab avalanches reported this week and potentially more that were unreported due to poor visibility the past few days.  

Avalanche Problem 1
  • 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

7” of new ‘upside down snow’ fell on 2/24 which has created a soft storm slab. 2” of additional snow from last night newly blankets the storm slab. Human triggered avalanches are possible, natural avalanches are unlikely. These Storm Slab avalanches will be small in size, 7” thick, and found at all elevations and on all aspects. Expect storm slabs to be inverted due to temperatures warming throughout the storm. Stiff snow over softer snow will be an indicator of this problem. This avalanche problem will improve within 24-48 hours. 

Hand pits, using small test slopes, and instability tests will help you identify this problem. Whumping and shooting cracks will be red flag clues for this avalanche problem. 

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.

Shooting cracks are a good indicator that you are traveling on unstable snow.

Hand pits are a quick easy way to identify poor structure in the upper snow pack. Yesterday hand pits were failing on isolation.

Avalanche Problem 2
  • 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 5 hours on 2/24. These winds have created small wind slabs in specific areas with slabs averaging 3-5” thick. These are located at upper elevations on west thru north aspects. These wind slabs will be small in size and human triggered avalanches are possible. Natural avalanches are unlikely.

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. Last night’s new snow will make identifying this problem more challenging. We expect this wind slab problem to be short lived and to diminish within 24-48  hours. 

Additional Concern
  • Dry Loose
    Dry Loose
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.
More info at Avalanche.org

Over the past 48 hours 9″ of new snow has fallen. This new 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 in isolated areas. Human triggered avalanches are possible and will be small in size. Natural avalanches are unlikely.

Weather
Thu, February 25th, 2021

New snow totals 2/21-25: 

Independence Mine: 9” of new snow

Frostbite bottom: 5″ of new snow

At the start of this week, temperatures were in the single digits with clear sky and calm winds. On 2/22 1” of new snow fell, and the temps remained cool. After this small amount of snow fell, the temperature dropped below zero for a short period of time. Starting 2/23 a storm system began moving into the Mat Su valley. On 2/24 temperatures began to rise quickly, and 6-7” of new snow fell in Hatcher pass. At the same time winds from the SE blew for 5 hours and was able to transport some of this new snow. After a brief break in the storm another 2-3” of new snow fell late last night and early this morning.


NWS Rec Forecast here.

NWS point forecast here.

State Parks Snow Report and Motorized Access information here.



Independence Mine 2/21-25: 


Marmot 2/21-25:

 

Observations
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