Hatcher Pass Avalanche Center
Hatcher Pass

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Issued
Mon, December 6th, 2021 - 7:00AM
Expires
Tue, December 7th, 2021 - 7:00AM
Forecaster
Jed Workman
Avalanche risk The Bottom Line

HEADS UP! A major wind event has rapidly increased the avalanche hazard overnight. This storm has brought more wind than new snow.

Human triggered wind slab avalanches will be likely, and natural avalanches will be possible. These avalanches will be large enough to bury, injure, or kill a person.

Wind slabs will be prevalent on West to North aspects at all elevations, with larger, more dangerous avalanches at the mid to upper elevations.

Mon, December 6th, 2021
Upper Elevation
Above 3,500'
3 - Considerable
Avalanche risk
Mid Elevation
2,500'-3,500'
3 - Considerable
Avalanche risk
Low Elevation
Below 2,500'
3 - Considerable
Avalanche risk
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
Avalanche risk Avalanche risk Avalanche risk Avalanche risk Avalanche risk
Travel Advice Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential. Very dangerous avalanche conditions. Travel in avalanche terrain not recommended. Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
Likelihood of Avalanches Natural and human-triggered avalanches unlikely. Natural avalanches unlikely; human-triggered avalanches possible. Natural avalanches possible; human-triggered avalanches likely. Natural avalanches likely; human-triggered avalanches very likely. Natural and human-triggered avalanches certain.
Avalanche Size and Distribution Small avalanches in isolated areas or extreme terrain. Small avalanches in specific areas; or large avalanches in isolated areas. Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas. Large avalanches in many areas; or very large avalanches in specific areas. Very large avalanches in many areas.
Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
  • 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

The avalanche hazard has rapidly increased overnight with SE winds averaging 29mph over the last 20 hours with a max gust of 52mph.

Winds will have drifted snow and built cohesive slabs up to a foot thick. These slabs will be sitting on old weak snow and will be easy to trigger.

SE winds will have built wind slabs in specific terrain on West to North aspects and we expect these to be about 1 foot thick this morning, with the potential to increase in thickness through the day with wind and new snow.

Shooting cracks, whumphing, and recent avalanches are all bull-eye clues for this problem.

Snotel stations are showing 0.2″ of SWE which translates to a few inches of new snow. New snow totals will be very difficult to assess due to the strong winds. Any snow that did accumulate will be wind effected and be contributing to the wind slab problem. A couple inches of new snow are expected today.

Once we are able to get into the field we will be able to get more information. There is some uncertainty predicting the thickness and size of wind slabs at this time.

Marmot Weather Station

 

Weather
Mon, December 6th, 2021

NWS AVG Forecast here.

NWS Rec Forecast here.

NWS point forecast here.

State Parks Snow Report and Motorized Access information here.

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