Hatcher Pass Avalanche Center

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sat, March 6th, 2021 - 7:00AM
Expires
Sun, March 7th, 2021 - 7:00AM
Forecaster
Allie Barker
The Bottom Line

Small sensitive wind slabs up to 7″ thick will be possible to human trigger at upper elevation on W to N aspects today. Dry loose sluffs will be possible to human trigger in terrain steeper than 40º at all elevations and all aspects. Persistent slabs will be possible to trigger today at all elevations, in specific locations on E to W aspects. Last weekend’s “drizzle” crust aka the “rashizzle” has been the culprit of rashes caused from crashing this week, ouch!  The crust varies in thickness with location but is reported to be widespread up to 5000′ at Hatcher Pass.

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Sat, March 6th, 2021
Upper Elevation
Above 3,500'
Moderate (2)
Avalanche risk
Mid Elevation
2,500'-3,500'
Moderate (2)
Avalanche risk
Low Elevation
Below 2,500'
Moderate (2)
Avalanche risk
Upper Elevation
Above 3,500'
Avalanche risk
Moderate (2)
Mid Elevation
2,500'-3,500'
Avalanche risk
Moderate (2)
Low Elevation
Below 2,500'
Avalanche risk
Moderate (2)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Recent Avalanches

No new slab avalanches have been reported since the Divide Ridge snogo triggered avalanche 3/2. See obs and pics HERE.

A few human triggered and a natural dry loose sluffs occurred on 3/3-3/4.

Natural dry loose, Skyscraper,  S, 4000′ 3/4

 

Natural, Dry loose, Skyscraper on SE/E aspect,4000′ of 3/1-3/3

 

Natural, Dry Loose, Liam’s Run NE 4000′ 3/2?

 

See the week of avalanche history HERE. in the mid-week conditions summary.

 

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

SE winds gusting 18-21 for 11 hours on 3/4-3/5 have formed shallow wind slabs on leeward aspects at upper elevation.

Small wind slabs up to 7″ thick will be possible to human trigger at upper elevation on West to North aspects today. Wind slabs may fail on top of the drizzle crust or beneath the crust depending on location. The crust is brittle and breakable to firm and stout depending on location.  Wind slabs that fail on the firm crust will have a challenging bed surface to maneuver off.

Faceting is occurring under and above this drizzle crust and will continue to be a layer of concern during the next storm or loading event.

It is unlikely, but not impossible that the wind slab could step down to the persistent slab 1-3′ deep in isolated locations.

 

Human triggered Wind Slab , N aspect 4500ft. 3/5

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

Small dry loose sluffs will be possible to human trigger today on steep slopes above 40º at all elevations. For the most part, sluffs are slow moving but they will require sluff management in steeper more committing terrain.  The smooth crust is making a nice bed surface for dry loose sluffs. Managing the “rashizzle” crust takes skill and continues to make us feel humbled. Catching an edge in the crust and getting caught in your sluff will be possible today.

Human triggered dry loose in steep terrain 3.4

 

Avalanche Problem 3
  • 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 1-3 feet deep will be possible to human trigger or remotely trigger today on East to West aspects, at all elevations today. The snowpack has poor structure and flaws that will continue to be problematic throughout our season. The persistent slab problem has and is expected to continue to fluctuate between dormancy and activity.  East and south aspects have a shallower and therefore weaker snowpack. West aspects have poor structure with the addition of a thick slab component from wind events throughout this season.

We have observed several small to large, 1-3 ft deep persistent slab avalanches both human and remotely triggered over the past week.  On 3/2 we saw a remotely triggered snowmachine avalanche that was capable of burying, injuring, or killing a person.

Test slopes, snowpits, slope cuts, previous tracks, and cornice drops can be misleading or unreliable tools for assessing this inherently dangerous and unpredictable avalanche condition. This low probability but high consequence hazard reminds us to be disciplined in implementing proper travel protocol in avalanche terrain. Ride one at a time, use appropriate safe zones, use communication, choose skin tracks and routes appropriately according to the danger of the day.

Divide Ridge avalanche , W 2700′ 3/2

2-3 ft crown depth at the Divide Ridge avalanche 3/2. This avalanche failed 15 cm above the ground on chained facets on an old wind slab.

Weather
Sat, March 6th, 2021

No new snow since 3/1

3/4-3/5  Marmot winds @4500′ gusted SE 18-21 for 11 hours.

Marmot 4500′ Last 24 hours:

NWS is calling for light westerly winds today with 50% chance of precipitation and 11-20ºF at 3000′.


NWS Rec Forecast here.

NWS point forecast here.

State Parks Snow Report and Motorized Access information here.

Observations
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