Hatcher Pass Avalanche Center

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sat, March 13th, 2021 - 7:00AM
Expires
Sun, March 14th, 2021 - 7:00AM
Forecaster
Allie Barker
The Bottom Line

The avalanche hazard is MODERATE today for Persistent Slab and Dry Loose. Persistent slabs up to D2 is size will be possible to human trigger on East through West aspects at all elevations. Small to large Dry loose sluffs will be possible to human trigger at all elevations and all aspects on slopes steeper than 40º. Natural avalanches are unlikely today.

Conditions have improved in much of the terrain at HP although buried crusts and wind pressed terrain still exist and present their own challenges. As we move into spring lets continue to practice Safe Travel Protocol. 

 

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Sat, March 13th, 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

Recent avalanches 3/10-3/12

A human triggered D1.5 slab occurred on 3/12 on the SSW face of Marmot at 4100′. It failed on the NSF under the sun crust/drizzle crust layer. It ran approx. 400 feet. The crown was approx. 4″ to 12″ deep.

Human triggered persistent slab, D1.5. SSW 4100′ 3/12 SS-ASu-D1.5-O

 

Close up of Human triggered persistent slab, D1.5. SSW 4100′ 3/12

 

Small natural slab avalanches were observed this week on E to W aspects at mid and upper elevation. We believe they occurred during the storm 3/10.

Marmot, West face 4000′ Remotely triggered from the ridge 3/10. Red line is the crown.

 

Debris from Marmot remotely triggered avy 3/10

 

Debris photo from above avalanche on Marmot west face 3/10

 

Slab avalanche on Hatch, North 3500′ 3/10? Unknown trigger

 

Multiple small dry loose sluffs were observed on many slopes steeper than 40º after 9″ of new snow this week.

Bullion mtn, Willow side, 4500′ SSE 3/10? Dry loose in the distance.

 

End of the Punk Spines, Natural dry loose 3000′ NNW 3/10?

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

Persistent slabs up to 12″ thick and D2 in size, will be ‘touchy to stubborn’ to human trigger or remotely trigger today on E through W aspects at all elevations although more likely on Southerly (SE,S,SW) aspects. On South aspects, a supportable stout sun crust has joined forces with the drizzle crust. Weak sugary snow from cold clear weather has formed near surface facets on top of and beneath these crusts. Both human and remotely triggered avalanches have failed on top of and beneath this mega crust this week and will continue to be a problem.  A couple inches of new snow from 3/11 blankets the snowpack and will make this problem visually less obvious. Pole tests, hand shears, or other instability tests will quickly reveal this problem.

The good news is that slabs formed by new snow and wind on 3/10 on all aspects are losing density (except southerly) , or acting less like a slab, from the cold temperatures over the past couple days. The bad news is the poor structure we have been witness to all season is still widespread at Hatcher Pass.  It will linger the rest of the season and become active again with additional loading events such as wind, snow or intense warming.

 

 

The human triggered avalanche on 3/12 failed on the NSF layer under the crusts seen in this picture.

Human triggered avalanche from 3/13  video here.

 

 

 

Sun crust has bonded with the drizzle crust on steep southerly aspects.

 

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

Dry loose sluffs will be possible to human trigger today on steep slopes greater than 40º on all aspects and all elevations.  Although sluffs were moving slower earlier in the week, cold temps have “dried out the snow” and will aid in sluffs moving faster today.  Crusts are acting as a smooth bed surface for sluffs and can catch you off guard.

Sluff management skills including avoidance are recommended.

As always, ski/ride one at a time, use appropriate safe zones for the danger of the day, and get out of harms way at the bottom of the slope.

 

Weather
Sat, March 13th, 2021

3/11-3/13: 0″ of new snow

Since Thursday , temperatures have dropped to -5º below zero and are 5.5ºF at 5am @ 4500′. Wind speeds remain low.

Temperatures will be 9-16ºF today with calm winds NE 0-7 mph. Clouds with some potential precipitation will move into the forecast zone Sunday afternoon. There is a 50% chance of snow Sunday night thru Tuesday morning.


NWS Rec Forecast here.

NWS point forecast here.

State Parks Snow Report and Motorized Access information here.


Independence Mine Temperature and Snow Depth 3/11-3/13

 

Marmot Winds 3/11-3/13

 

Observations
Recent Observations for Hatcher Pass