Hatcher Pass Avalanche Center

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sat, December 14th, 2019 - 7:00AM
Expires
Sun, December 15th, 2019 - 7:00AM
Forecaster
HPAC Staff
The Bottom Line

We are in a unique avalanche paradigm, with areas of very good stability mixed with specific locations that contains glide avalanche hazards, which are unpredictable and dangerous, but fortunately fairly easy to identify and avoid.

The overall avalanche hazard is low at all elevations, except in areas with glide cracks and/or old glide avalanche activity. Natural glide avalanches are still possible, will be difficult to predict the timing of release, and will be large enough to bury, injure, or kill a person.

This unique avalanche conundrum is best handled by avoiding any area with “brown frowns”, glide cracks, or previous glide avalanche activity.

Click here for recent surface conditions photos.

 

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Sat, December 14th, 2019
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

Observed new glide avalanches this week: South face, Sunnyside, Hatch Peak. South face of Idaho Peak.

Observed new glide cracks forming: SW face Marmot (Catcher’s Mitt, see photo under avalanche problem 1).

12/8/2019 – Glide avalanche on Hatch Peak, ESE, 4000′

 

Glide cracks on the SW face of Marmot. Viewer’s left and middle – growing glide cracks. Right – old glide avalanche release.

 

Photo: 12/13/2019 – Glide Crack, Upper Willow Creek, ESE, 4400′. Highmarks are not a sign of stability, this glide crack may release at any time.

 

Strong southeast winds Saturday through Tuesday transported available snow and built winds slabs on leeward aspects, west to north. These instabilities were significant, but short lived. On December 8-9 numerous small to large, 1.5 foot deep, human triggered winds slab avalanches occurred on these aspects, on Rae Wallace and Microdot. The avalanche on Microdot caught and carried a person who triggered their airbag, no injuries. Avalanches in Rae Wallace caught and carried skiers who were able to self arrest on the bed surface, no injuries. One large natural wind slab avalanche was observed in Delia Creek.  See more information in the observations platform, including a video of a person triggering a wind slab on Microdot here.

 

Avalanche Problem 1
  • Glide Avalanches
    Glide Avalanches
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
Glide Avalanches
Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.

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

Glide avalanches continue to be a widespread, low probability, high consequence hazard. These avalanches can fail at the ground, 2-4 feet deep, releasing the entire depth of the snowpack as a unit. Glide avalanches may release at any time, are unpredictable, and can be large enough to bury, injure, or kill a person.

Identifying and avoiding glide cracks is fairly easy and substantially increases your level of safety. You may see other people skiing, riding, or snow machining, near, over, or around glide cracks, however, this is not an indication of stability. Human triggering a glide avalanche is extremely unlikely, and the timing of when a glide releases is highly unpredictable.

Fortunately, avoiding this hazard is fairly easy. Glide cracks visually stand out on the landscape and appear as “brown frowns” (see picture below for reference). Glide cracks can be a single brown frown or a series of cracks. These cracks indicate the snowpack is creeping, which is an extremely slow paced motion down-slope which culminates in the release of the entire snowpack. Glide cracks can exist for seconds or months before the resulting avalanche occurs and is therefore extremely difficult to predict.

12/13/2019 – Glide crack on the SW face of Marmot Mountain at 3600′. This crack has grown over the last few days.

While glide avalanches are difficult to predict, their consequences are easy to understand. We can’t tell you what the probability of a given glide avalanche releasing is, but it is something akin to Russian Roulette, which we actually understand the odds of much better. So while you or other people may get away with traveling in or around glide avalanches, and this may happen with some frequency, don’t forget that in doing so, you are risking your life.

Weather
Sat, December 14th, 2019

A low pressure system moving up the Aleutian chain and into the gulf of Alaska this weekend through mid week is not likely to bring Hatcher Pass much, if any, precipitation. Temperatures will hover around freezing at 3000′ and cool overnight through the weekend. This week’s temperatures are forecasted to cool. Winds should remain light.

Stability is expected to remain the same and stagnate through the weekend and into the early week.

NWS Rec Forecast here.

NWS point forecast here.

State Parks Snow Report and Motorized Access information here.

Observations
Recent Observations for Hatcher Pass