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 22nd, 2022 - 7:00AM
Expires
Fri, December 23rd, 2022 - 7:00AM
Forecaster
Jake Kayes
The Bottom Line

Strong winds from the East have transported snow and created wind slabs 3 to 5 inches thick. 

Human-triggered wind slabs are possible at upper elevations on westerly aspects and leeward features. These avalanches will occur on slopes 35º or steeper. 

Human-triggered persistent slab avalanches are possible in isolated areas at mid and upper elevations on southerly aspects. These avalanches will occur on slopes 30º and steeper.

Natural avalanches are unlikely. 

Winds are forecasted to increase in the afternoon, with extreme winds forecasted for Thursday evening thru Friday. Avalanche danger will increase rapidly during this wind event.

Thu, December 22nd, 2022
Upper Elevation
Above 3,500'
Moderate (2)
Avalanche risk
Mid Elevation
2,500'-3,500'
Moderate (2)
Avalanche risk
Low Elevation
Below 2,500'
Low (1)
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
Low (1)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Recent Avalanches

There have been a few small loose dry avalanches triggered in steep terrain in the last week. No human-triggered or natural slab avalanches have been observed since 12/15.

Loose Dry avalanche near Martin Mine 12/20

Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
  • Almost 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

Overnight winds from the East with gusts up to 27 mph lasted for 6 hours and have created wind slabs 3-5” thick. Human-triggered wind slabs will be possible at upper elevations on westerly aspects on slopes 35º or steeper. Wind slabs will be found near ridge tops and on leeward features. These avalanches will be small in size. Natural avalanches are unlikely. 

Wind effect and texture on Sky Scraper 12/21.

Wind texture and effect on Bullion Mountain 12/21.

These freshly formed wind slabs will be sitting on weak sugary faceted snow that formed during recent cold weather. We expect these wind slabs to gain strength very slowly. 

To identify this avalanche problem look for smooth wind drifted snow. Hand pits, pole probes, and other traveling tests will help you identify this avalanche problem. Formal stability tests will also help you identify this problem. 

Shooting cracks and collapsing will be red flags for this avalanche problem. 

Avalanche Problem 2
  • 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

Persistent slab avalanches will be possible in isolated areas on southerly aspects at mid and upper elevations on slopes 30º and steeper. These avalanches will be large in size and fail near the ground. Natural avalanches are unlikely. 

In areas where the snowpack is shallower, it will be more likely for humans to trigger a persistent slab avalanche. Use your pole or probe to measure snowpack depth as you’re traveling in the mountains. 

The snowpack is slowly gaining strength and it has been a week since any persistent slab avalanches have been observed. This avalanche problem will be difficult to trigger and the consequences will be high.

 

Weather
Thu, December 22nd, 2022

Extreme winds are forecasted for Friday 12/23 for Hatcher Pass

 

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.

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