Hatcher Pass Avalanche Center

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Thu, November 23rd, 2023 - 7:00AM
Fri, November 24th, 2023 - 7:00AM
Allie Barker
Avalanche risk The Bottom Line

The avalanche hazard is MODERATE for PERSISTENT SLABS on all aspects, at all elevations, on slopes steeper than 30º.

You are most likely to trigger an avalanche where the wind has formed drifts or stiffened snow surfaces. Slabs will be thickest above 3500 feet. Large avalanches failing on weak faceted snow near the base of the snowpack will be possible to human trigger.

Strong wind early in the week has transformed and scoured much of the terrain at Hatcher Pass creating variable conditions with firm surfaces, sastrugi, and few pockets of powder.  Low angle protected terrain will be the best choice for enjoying the backcountry today.

Special Announcements
Wednesday, November 29, 6:00PM
Bearpaw River Brewing Company Taproom (Palmer-Wasilla Hwy)

Join HPAC as we host local guide, avalanche instructor, and author Joe Stock for a presentation marking the release of his newest book, “The Avalanche Factor.” Joe will talk about the book and dive into one of its topics, luck and avalanches.

Thu, November 23rd, 2023
Upper Elevation
Above 3,500'
2 - Moderate
Avalanche risk
Mid Elevation
2 - Moderate
Avalanche risk
Low Elevation
Below 2,500'
2 - Moderate
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

Two small natural wind slabs were observed in the Firn path off Marmot and Marmot 1 gully that occurred as a result of the wind event on 11/20 (no pics). No other recent avalanches were observed on Friday.

Two avalanches were remotely triggered on Saturday, 11/18 seen below. More info in obs here.

11.18 Cracking that occurred during a skier descent on the SW face of Marmot that additionally remotely triggered two avalanches on opposite sides of the mountain.

11.18 Death Gully, remotely triggered by skier on SW face several hundred yards away. SS-ASr-D2.5-O

11.18 Looking up at the Death Gully avalanche

11.18 Death Gully avalanche crowns and runnout

11.18 Marmot SE face (Marmot2 gully) remotely triggered by skier on SW face. SS-ASr-D1.5-O

Recent Conditions

Unfortunately, Mondays wind event transformed HP from the powder haven it was just a week ago.

11.22 Marmot south ridge wind textured surfaces are contributing to variable conditions.

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

Persistent slabs up to 3 feet thick will be possible to human trigger in specific locations, on all aspects, at all elevations.  We saw evidence of this problem with last Saturdays two remotely triggered avalanches followed by Mondays wind event which loaded leeward slopes, adding stress to an already weak snowpack.  The good news is the continuity of the weak layer does not exist everywhere so finding a slab/weak layer combo may be challenging/less likely. The bad news is if you do find a location where this recipe exists, triggering a large avalanche will be possible.

Remotely triggered avalanches will be possible from below, above, or adjacent to slopes.  This type of avalanche problem often gives unreliable feedback.  Cracking and whumping may or may not occur prior to triggering an avalanche. Pole/probe tests and formal stability tests will help you identify stiffer snow over weaker snow and where this problem exists.

Expect the persistent slab problem to become more reactive with the next storm cycle or loading event.

The video below is from our tour on Friday and shows propagation on the basal facet layer near the ground with ECT and PST instability tests. More info in Friday observations here. 

Winds continued to gust from the southeast from 30-34mph for 7 hours overnight before calming down early this morning. You may encounter a few thin winds slabs today. Expect them to be isolated, stubborn and and bonded well especially with todays mild weather hovering around 30ºF at 3000 feet. Most importantly, wherever wind slabs exist expect the persistent weak layer to be more of a problem.

If you head into avalanche terrain today, utilize strict safety travel protocols, travel one at a time from safe zone to safe zone, only have one person on slope at a time, ensure all members of your party are carrying and know how to use beacons, shovels and probes, and avoid slopes with terrain traps.

Thu, November 23rd, 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