Hatcher Pass Avalanche Center

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Thu, January 21st, 2021 - 7:00AM
Expires
Fri, January 22nd, 2021 - 7:00AM
Forecaster
Jake Kayes
Conditions Summary

Today’s avalanche problems will be wind slab, persistent slab and dry loose, human triggered avalanches are unlikely. Triggering an avalanche in isolated or extreme terrain is still possible.

New snow this week has covered rocks and other hazards sitting just below the surface, even a small avalanche could have high consequences.

Riding conditions have improved dramatically in areas protected from the wind.

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Thu, January 21st, 2021
Recent Avalanches

There were two human triggered avalanches this week.

On Monday 1/18 two small human triggered wind slabs was reported on lower thousand dollar run, North 3000′. Click here for more info. 

On Tuesday 1/19  a small human triggered soft slab was observed on Presidents Ridge, ENE 2800′. Click here 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

Light winds from the southwest have transported snow and created soft wind slabs 3-4” thick. Expect to find these wind slabs at upper elevations on northeast aspects and near ridge tops. The new snow that fell was very low density and was easily transported by light winds. 

Low density snow that fell on 1/19 was transported by light winds, signs of wind transport can be seen throughout the area. We believe that wind slabs have formed in isolated areas and that this avalanche problem will be small in size due to the very low wind speeds. We also believe that if you do trigger one of these avalanches that they will likely run very short distances. 

That being said, even a small wind slab can sweep you through rocks or other hazards and cause traumatic injury.

Use hand pits and pole tests to identify soft pillows or drifted snow overlying weaker snow. Shooting cracks will be a red flag for this avalanche problem. 

Ski penetration and overall snowpack depth is highly variable.

Where did the 6-8″ of new snow go?

Sunny side of Hatch peak. Signs of wind transport can be seen near ridge tops.

Avalanche Problem 2
  • Persistent Slabs
    Persistent Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    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

Persistent slabs will be unlikely at all elevations and aspects. Small avalanches are unlikely but still possible in very isolated or extreme terrain.

An observation from 1/19 is a good example of the size of persistent slab avalanches you might encounter in Hatcher Pass today.

This week’s new snow was not enough of an additional load to reawaken our persistent slab problems deeper in the snowpack. The snowpack still has poor structure but is gaining strength slowly. 

Any avalanche triggered has increased consequences of traumatic injury, due to the high likelihood of being swept through rocks or other obstacles.

We recommend using safe travel techniques anytime you are traveling on or near avalanche terrain. Use adequate spacing when traveling uphill, ride down one at a time, spot your partners, and choose safe zones that are out of harm’s way. Avoid slopes with any terrain trap below.

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

The 6-8” of low density snow that fell earlier in the week will be capable of producing dry loose avalanches in protected terrain that is 40° degrees or steeper. Human triggered avalanches are possible and will be small in size. 

Weather
Thu, January 21st, 2021

New snow totals 1/17-21

Independence Mine: 6″ of new snow


Good news Hatcher Pass has finally gotten some new snow this week! Overall the weather has been all over the place, but most importantly the pass was spared from rain. On Jan 17th temperatures at Independence Mine started at 33°F but began to decrease into the mid 20s, and a trace amount of new snow fell. As temperatures dropped and snow began to fall, winds from the southeast began to increase and gusts reached 54mphs at Marmot station. These winds did not decrease 17 hours and lasted well into the day on the 18th. On Jan 19th 6-8” of low density snow fell giving Hatcher Pass a much needed refresh. This snow was transported by light winds and has exposed ridgetops once again.


NWS Rec Forecast here.

NWS point forecast here.

State Parks Snow Report and Motorized Access information here.


Marmot 4500′ 1/17-21

 

 

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