Hatcher Pass Avalanche Center

Hatcher Pass RSS

ARCHIVED - Forecasts expire after 24 hours.
Sat, December 2nd, 2023 - 7:00AM
Sun, December 3rd, 2023 - 7:00AM
Jed Workman
Avalanche risk The Bottom Line

Human-triggered, large avalanches failing at the ground up to 3 feet deep will be possible today on all aspects at mid to upper elevations.

The good news is the weak layer at the base of the snowpack, which has been problematic so far this season, is slowly improving in stability.

The bad news is this layer is persistent and lingering, and triggering a large avalanche is still possible.

Yesterday’s forecaster observation from the field HERE.

Sat, December 2nd, 2023
Upper Elevation
Above 3,500'
2 - Moderate
Avalanche risk
Mid Elevation
2 - Moderate
Avalanche risk
Low Elevation
Below 2,500'
1 - Low
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.
Recent Avalanches

No new avalanches were observed on 12/1/23.

A few recent avalanches were observed on 11/29 including those seen below in Rae Wallace D1.5-2.

The  11/29 wind event was strong and transported available low-density snow, overloading a basal weak layer and also producing some avalanches on storm snow interfaces. Wind slabs were active during and just after the wind event on 11/29, however, since then, they have bonded well to precipitaion particles which they sit on.  Therefore, wind slabs have been removed from the avalanche problem list since the last forecast.

11/27/21 – Rae Wallace, NW, upper elevation, four small to large natural avalanches, failed on persistent facets/sugar snow near the ground.

11/27/23 – Near Baby Ruth, ENE, Mid-Elevation, large natural avalanche failed due to wind loaded. Likely failed on persistent faceted/sugar snow near the ground. Red arrow points to crown, circle encompasses debris field.


12/1/23 – Recent widespread winds have sculpted the snow surface with sastrugi, scalloping, and breakable wind crusts. Locations with soft powdery snow are few.

Recent Conditions

Recent widespread winds have sculpted the snow surface with sastrugi, scalloping, and breakable wind crusts. Locations with soft powdery snow are few.

Wind damage on Punk Spines

Avalanche Problem 1
  • Persistent Slabs
    Persistent Slabs
  • Certain
    Very Likely
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
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 basal persistent weak layer near the ground consists of old, unconsolidated sugary snow from October. This layer has plagued Hatcher Pass this season and is the main culprit in most avalanches so far. The good news is we are seeing a trend towards better stability. The bad news is avalanches up to 3 feet thick continue to be possible and stubborn to trigger on all aspects at mid and upper elevations on slopes 35º and steeper. Natural avalanches are unlikely.

The upper elevations present the greatest hazard, where temperatures have been colder and the basal persistent weak layer is better preserved. In the mid-elevations, we have seen significant improvements in the stability of the snowpack, but can not remove the possibility of triggering large avalanches here yet.

Snowpack depth varies, generally thicker depths on the North and Western aspects where prevailing winds have deposited snow throughout the season. The South and East aspects, where prevailing winds have scoured snow throughout the season, are generally shallower. This is a tough conundrum since shallower areas will be easier to human trigger, and locations with deeper snowpacks will be harder to trigger, but larger and more dangerous avalanches will be possible.

This type of problem may allow several people to travel without incident, and then be triggered by the next person on slope. In this scenario, we continue to recommend attention to safe travel protocol. Spread out, only one person on the slope at a time, identify and use safe zones, don’t group up at the base of avalanche terrain. Avoid slopes with terrain traps, and choose slopes with gentle, fanning runouts.

Recent avalanches, whumphing, collapsing, and shooting cracks are red flags for this problem.

More details:

Previous warmth, moisture, and rain allowed basal facets to round and increase in stability. Observations to up to 4500′ have verified increased stability, but propagation and therefore human triggered avalanche potential still lingers. We have not gone above 4500′ in observations this season. Any avalanche triggered could fail at the ground, releasing the entire snowpack, resulting in a large avalanche capable of injuring, burying, or killing a person. The snowpack is thicker on W to N aspects (clockwise) and therefore any avalanche failing on the basal layer in these areas will be larger in size.



Sat, December 2nd, 2023

NWS AVG Forecast here.

NWS point forecast here.

Marmot Weather Station here.

Independence Mine Snotel here.

Frostbite Bottom Snotel here.

State Parks Snow Report and Motorized Access information here.

XC trail grooming report for Mat-Su, Anchorage, and Kenai here.

Recent Observations for Hatcher Pass