Hatcher Pass Avalanche Center
Hatcher Pass

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Thu, December 15th, 2022 - 7:00AM
Expires
Fri, December 16th, 2022 - 7:00AM
Forecaster
Jake Kayes
The Bottom Line

The avalanche danger is considerable at all elevations.

Overnight the forecast area has received 10-12 inches of new snow and .9″ of SWE.

Human-triggered persistent slab avalanches 3-5 feet thick will be likely at all elevations and all aspects on slopes 30º and steeper. These avalanches will be large in size.

Human-triggered loose dry avalanches 10-12 inches deep will be likely at all elevations and on all aspects. On slopes 40º and steeper. These avalanches will be small in size.

Natural avalanches are possible. 

Since 12/12 Hatcher Pass has received 38 inches of snow and 3.4 inches of SWE.

There will be an end to all this snowfall! The current storm will end this afternoon, expect new snow to taper off, temperatures to drop and the sky to clear. 

Thu, December 15th, 2022
Upper Elevation
Above 3,500'
Considerable (3)
Avalanche risk
Mid Elevation
2,500'-3,500'
Considerable (3)
Avalanche risk
Low Elevation
Below 2,500'
Considerable (3)
Avalanche risk
Upper Elevation
Above 3,500'		 Avalanche risk
Considerable (3)
Mid Elevation
2,500'-3,500'		 Avalanche risk
Considerable (3)
Low Elevation
Below 2,500'		 Avalanche risk
Considerable (3)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Recent Avalanches

Numerous large natural avalanches were observed on Wednesday 12/14. There were likely more avalanches that occurred but poor weather inhibited our ability to see many locations.

Stairstep NW 3200′. D2 persistent slab avalanche. 12/13/22

Arkose 1 slide path. West 3600′ D2+ persistent slab avalanche. 12/13/22

Punk Spine, West 4100′ D2 persistent slab avalanche. 12/13/22

Government Peak area, East 4200′. D2 persistent slab avalanche on saddle between Peak 4600′ and Government. 12/13/22

Sunny Side of Hatch, East 4200′. D2+ persistent slab avalanches. 12/13/22

Avalanches not pictured:

Idaho Peak South 2700-3200′ several D2 persistent slab avalanches.

Arkose Waterfall slide path, West 3500′ D2 persistent slab avalanches.

Avalanche Problem 1
  • Persistent Slabs
    Persistent Slabs
  • Almost 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

The 39 inches of new snow that have fallen this week, has stressed weak faceted snow at the bottom of the snowpack. Human-triggered persistent slab avalanches will be likely at all elevations on all aspects, on slopes 30 degrees and steeper. Natural avalanches are possible. These avalanches will be large and capable of causing entire slopes to avalanche.

Lower punk spines NW 2400′ D2 persistent slab slab avalanche. 12/13/22

While in the field yesterday forecasters observed widespread natural avalanches that failed at the ground. These avalanches occurred at all elevations and all aspects. The snowpack still has flawed structure and will need time to adjust to all the new snow that fell over the last week.

As the weak sugary faceted snow at the ground gets buried deeper avalanches will be harder to trigger but the consequences of an avalanche will grow. Any persistent slab avalanche that is triggered will be large enough to bury, injure or kill a person. 

The persistent slab problem is now buried deep enough that formal stability tests may not provide reliable information. It will be more important to identify the structure and determine if cohesive snow is sitting above weak faceted snow at the ground. Due to the depth of the weak layer, shooting cracks or collapsing may not be observed before triggering an avalanche. 

Snow stake at 4am this morning.

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

The 10-12” of new snow that fell overnight will be capable of producing small loose dry avalanches. Human-triggered loose dry avalanches are likely on slopes over 40º. Natural avalanches are possible. The drizzle crust that formed on December 13th will act as a bed surface for loose dry avalanches.

This drizzle crust will be found at lower and mid elevations, forecasters have yet to verify how high in elevation this crust formed. 

Hand pits and other traveling tests will be good tools to identify this avalanche problem.

Weather
Thu, December 15th, 2022

NWS AVG Forecast here.

NWS point forecast here.

Marmot Weather Station here.

Independence Mine Snotel here.

State Parks Snow Report and Motorized Access information here.

Observations
Recent Observations for Hatcher Pass