Hatcher Pass Avalanche Center

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Thu, December 24th, 2020 - 7:00AM
Expires
Fri, December 25th, 2020 - 7:00AM
Forecaster
Jake Kayes
Conditions Summary

Today’s avalanche problem will be persistent slab. Human triggered persistent slab avalanches will be possible at all elevations. Natural avalanches are unlikely. Hard stiff snow that overlies weak sugary snow, will be a sign that persistent slab avalanche problems are present.

Remote triggering an avalanche is still possible, choose safe zones carefully and watch out for steep terrain above you. There were a few remotely triggered avalanches this week.

Coverage is still thin in some areas. Getting caught in an avalanche will have increased consequences, due to the potential of being swept through thinly covered rocks and other hazards.

Winds this week have taken their toll on the forecast area. The snowpack depth is highly variable, with depths ranging from bare ground near ridge tops, to over 4’ deep on west through north aspects. Riding conditions deteriorated with strong winds earlier this week. 

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Thu, December 24th, 2020
Recent Avalanches

We had several natural avalanches and at least two human triggered avalanches this week. April bowl had a large natural avalanche occur on either 12/21-22 see photo below.

12/21: A user reported a remote triggered avalanche, Government peak area 3000′, click here for more info


12/22: A large natural avalanche was observed on Ray Wallace NW 4500′, this avalanche occurred in the chute commonly used for ascent.

Two remote triggers occurred above the sledding hill, see photo below.

A report of a possible remote trigger or natural avalanche. NW 4003′ near cross hill. For more info click link here


12/23: A user reported a natural avalanche in the Government peak area, NE 2000′. Click here for more info.

Forecasters observed a natural avalanche occurred on the Lodge run on Marmot, W 4300′.


 

April Bowl N/NW 4700′
Natural D2 likely occurred on 12/21 or 12/22

Above sledding hill. W 3400′ Remote triggered from 200′ away on 12/22

 

Avalanche Problem 1
  • 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

Human triggered avalanches are possible at all elevations on southwest through northeast aspects, in terrain 30 or steeper. Natural avalanches are unlikely. These avalanches will be large enough to bury, injure or kill a person. It’s important to remember that the extreme winds earlier in the week have created irregular loading patterns. Extreme wind speeds can form slabs mid slope and catch you by surprise.

Due to poor visibility and travel conditions, we have limited information on south facing slopes. It’s reasonable to expect that cross loaded gullies on south facing slopes will have this persistent slab problem.

The snow pack currently has two weak sugary layers. One is closer to the surface and consists of rounding facets. This layer is buried anywhere from 1-3’ from the surface and has been very reactive this week. These rounding facets were responsible for the remote triggered avalanches on 12/22.

The second layer consists of basal facets(weak sugary snow near ground) this layer has been reactive in snow pits this week. On 12/21-21 a natural avalanche on April Bowl occurred and appears to have started in the rounding facets and stepped down into the basal facets.

Hard dense snow sitting over less dense snow, should be given extra caution. Shooting cracks, collapsing and whumping will be red flags for this avalanche problem. Hand pits, pole tests and instability tests will help you identify the persistent slab problem. 

This week there were at least two remote triggered avalanches. One of these avalanches was triggered from at least 200’ feet away. Disciplined safe travel procedures, will help increase your margin of safety when dealing with the possibility of remote triggering an avalanche. 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. 

The extreme winds this week have created dense stiff sitting on weak snow. These hard slabs will allow you to travel out onto a slope before failing above you making escape difficult to impossible. Avoid cross loaded gullies and slopes with old stiff snow. Choose slopes that have safe run-outs and avoid any slope with terrain traps below.

Marmot SW face showing signs of cross loading and some cool wind texture on the snow.

 

Avalanche debris above the sledding hill. 3400′ West

 

Looking towards Hatcher Pass and scoured ridges. 12/23

Weather
Thu, December 24th, 2020

New snow 12/20-24

Independence Mine: 14″

Frostbite Ridge: 6″


This week had some exciting weather with new snow and extreme winds! On sunday independence mine received 8” of new snow, temps remained in the single digits. On monday winds increased at Marmot and Independence Mine with gusts reaching 28 mphs these winds lasted for approximately 8 hrs. Late monday winds increased, with gusts reaching almost 50mphs at both the marmot and independence mine. These winds lasted from around 14hrs. On Wednesday winds tapered and another 8” of new snow fell at independence mine. 


NWS Rec Forecast here.

NWS point forecast here.

State Parks Snow Report and Motorized Access information here.


Independence Mine 12/20-24:

 

 


Marmot 12/20-24:

 

 


Frostbite ridge 12/20-24:

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