Hatcher Pass Avalanche Center
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Issued
Thu, November 26th, 2020 - 7:00AM
Expires
Fri, November 27th, 2020 - 7:00AM
Forecaster
Jake Kayes
Conditions Summary

Bottom Line

Today’s avalanche problems will be wind slab, storm slabs, and persistent slab avalanches. Human triggering wind slabs will be likely, and storm slabs and persistent slabs are possible.

New snow and significant winds from last night have drastically changed conditions in the forecast zone. Remember most avalanches occur within 24-48 hours of a storm. Shooting cracks, whumping, and smooth pillow like snow, will all be red flags to watch out for today.

Coverage will still be thin at higher elevations. Any avalanche triggered could carry a person through thinly buried rocks or other hazards. 

For more details of this week’s weather and the current storm check the weather tab.

 

Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    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

Strong S/SE winds overnight transported snow for 8 hours at upper elevations, forming small wind slabs that are 6-10” in thickness. Expect to find these on southwest through northeast aspects above 3500’. These wind slabs will be likely triggered by humans on slopes 35° degrees or steeper, natural avalanches are possible. Small winds slabs will be in specific locations on leeward aspects, with large slabs in isolated locations.  These slabs could be hard to detect underneath the new snow from the tail end of the storm.

Stiff snow overlying weaker snow, wind pillows, and cracking will all be red flags for this avalanche problem. Use hand pits and pole tests to identify the presence of stiffer snow on top of weaker snow.  

 

Wind transport on Marmot’s Ray Wallace chutes.

 

Wind scouring on Eldorado Bowl

 

Cross loaded gullies on Marmot

Avalanche Problem 2
  • Storm Slabs
    Storm Slabs
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    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

Seven inches of snow fell last night at Independence mine. Cool temperatures prevented storm snow from bonding well with the old snow surface. Human triggered avalanches will be possible, natural avalanches unlikely. This avalanche problem will be found on all aspects and elevations.

Loose dry avalanches will also be a problem today. Human triggered avalanches are likely in terrain over 40 degrees.

Avalanche Problem 3
  • Persistent Slabs
    Persistent Slabs
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    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

Recent winds and snow have stressed weak sugary snow at the bottom of the snowpack. Human triggered avalanches will be possible and natural avalanches will be unlikely. This avalanche problem will be found on all aspects and elevations but will be more prevalent at mid elevations.  

The poor structure in the snowpack is still suspect. Facets at the ground still were reactive in snow pits on wednesday. This loose sugary snow at the base of the snowpack is capped with a thin melt freeze crust. 

 

Basal facets 1-2mm that have begun round. Some striation was observed.

 

Facets have matured in areas with thinner coverage

 

Eldorado with thinner coverage at higher elevations

Weather
Thu, November 26th, 2020

11/26 Storm snow totals

Skeetawk:

6″ new snow           1″ SWE

Independence Mine:

7″ new snow          .7″ SWE

Marmot:

Max Gust: 36 mph SE       Average Gust: 24mph

Average sustained winds: 12 mph

On Sunday 11/22 4” of new snow fell at independence mine. Light to moderate wind from the east blew for 8 hours Monday morning. This was able to transport some snow and create some small wind slabs. Tuesday was relatively calm with light winds and temperatures dropping into the teens. Wednesday’s winds were sustained for 14 hours, with sustained winds of 26mph and gusts upto 36 mph. This was able to scour a large amount of terrain and create some new wind slabs. Upper elevations were affected the most by these winds and coverage can be thin in some areas.

Throughout the week temperatures have been colder at higher elevations. On Monday all weather stations saw some warming with Independence Mine reading 29°F midday. Temperatures cooled again Tuesday with Marmot reaching the low teens in the morning. On Wednesday temperatures began to increase with the arrival of storm systems.

 

NWS Rec Forecast here.

NWS point forecast here.

State Parks Snow Report and Motorized Access information here.

Independence Mine:

11/22-11/26

 

Marmot: 

11/22- 11/26:
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