Hatcher Pass Avalanche Center
Hatcher Pass

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ARCHIVED - Forecasts expire after 24 hours.
Issued
Thu, November 30th, 2023 - 7:00AM
Expires
Fri, December 1st, 2023 - 7:00AM
Forecaster
Allie Barker
Avalanche risk The Bottom Line

The potential for large avalanches to fail in weak, deeper snow still exists in specific locations at upper elevation.

Strong wind on Tuesday has redistributed new snow and formed variable wind slabs in many locations that are mostly unreactive and will make it challenging to have your best day ever.

Stability continues to improve at mid and low elevation.

Special Announcements

Please welcome Ryan Lewthwaite to the HPAC forecaster team! Ryan comes to us most recently from the Mount Washington Avalanche Center. Welcome Ryan!

Thu, November 30th, 2023
Upper Elevation
Above 3,500'
2 - Moderate
Avalanche risk
Mid Elevation
2,500'-3,500'
2 - Moderate
Avalanche risk
Low Elevation
Below 2,500'
1 - Low
Avalanche risk
Fri, December 1st, 2023
Upper Elevation
Above 3,500'
2 - Moderate
Avalanche risk
Mid Elevation
2,500'-3,500'
2 - Moderate
Avalanche risk
Low Elevation
Below 2,500'
1 - Low
Avalanche risk
Fri, December 1st, 2023
Upper Elevation
Above 3,500'
2 - Moderate
Avalanche risk
Mid Elevation
2,500'-3,500'
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

A few recent avalanches were observed on 11/29 including this one seen below in Rae Wallace D1.5-2. Photo was taken from a long distance on a poor vis day. Squint and you can see a sizable crown that propagated to the ridge. Debris is visible almost reaching the drainage at the base of Rae.

Rae Wallace natural 11/29

Same avalanche in Rae Wallace

A few other avalanches were observed on Wednesday in the Found Couloir (next to Lost couloir) near Birthday Pass and Point of Interest above Gold Mint parking lot.

Strong wind from Tuesday redistributed new snow making it challenging to see recent avalanches from earlier in the week.

Recent Conditions

Many locations remain scoured by recent winds including the Pinnacle seen in the distance here.

Avalanche Problem 1
  • Persistent Slabs
    Persistent Slabs
  • Aspect/Elevation
  • 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.
Aspect/Elevation of the Avalanche Problem
Specialists develop a graphic representation of the potential distribution of a particular avalanche problem across the topography. This aspect/elevation rose is used to indicate where the particular avalanche problem is thought to exist on all elevation aspects. Areas where the avalanche problem is thought to exist are colored grey, and it is less likely to be encountered in areas colored white.
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 stubborn yet still possible to human trigger on West to Northeast aspects (clockwise) at upper elevation on slopes 35º and steeper. Natural avalanches are unlikely.

It will also be possible for isolated wind slabs to step down and fail in the weak basal facets at upper elevation on leeward aspects.

In general, we have seen less propagation in our pits this week as seen in Wednesday’s obs.  Even though the weak sugary basal facet layer has high continuity and can be found buried on all aspects above 3500-4000′, it is only a problem where a slab overlies this weak snow. Strong southeast winds are the main culprit for building new slabs on leeward aspects this week. Be suspect of these locations.

Wind effect from numerous days of strong wind transport seen here on the top of Marmot.

Prominent wind loading this week. Slabs overlying weak snow are more likely to be found on West to NE aspects.

We expect this avalanche problem will continue to linger at upper elevation.  Each time the snowpack is freshly loaded, expect to see natural avalanche activity.

Avalanche behavior will be difficult to predict. Use safe travel protocols to increase your margin of safety.

At mid and low elevation, stability is improving as a result of a more homogenous snowpack compared to upper elevation. This will be a good base for future storms.

Weather
Thu, November 30th, 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.

Observations
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