Hatcher Pass Avalanche Center
Hatcher Pass

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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sat, November 26th, 2022 - 7:00AM
Expires
Sun, November 27th, 2022 - 7:00AM
Forecaster
Jed Workman
Avalanche risk The Bottom Line

At the mid to upper elevations, it will be possible to human-trigger a 1-3’ thick persistent slab avalanche failing on weak sugar snow near the ground in specific locations such as previously wind-loaded slopes and features on Southwest to Northeast aspects. Overnight shifting winds and freshly drifted snow at the upper elevations may add complexity and uncertainty to the exact aspects where triggering a persistent slab is possible.

Small Wind Slabs will have formed over the last 48 hours at the upper elevations along ridgelines and these will be possible to human-trigger today. The aspect distribution of this problem may be patchy and difficult to predict due to a lack of accurate wind data and shifting winds.

Loose Dry avalanches will be possible to trigger on all aspects on slopes 40 degrees and steeper.

Natural avalanches are unlikely.

Triggering any avalanche and getting caught carries the added consequence of impacting rocks due to overall shallow coverage and early season conditions.

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Sat, November 26th, 2022
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

The last human-triggered avalanche was reported on Nov 16th, 10 days ago. No natural avalanches have been observed over the last week. 

Yesterday’s visibility was extremely limited due to the weather. We were not able to see any signs of new storm-related avalanches, but the weather limited our ability to see many areas. If you get out today, please contact us and/or send pictures through observations as soon as possible if you see any avalanches.

Avalanche Problem 1
  • Persistent Slabs
    Persistent Slabs
  • 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.
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

It will be possible to human trigger slab avalanches in specific locations at the mid and upper elevations where previous wind loading (11/13-14) transported and deposited snow, overloading the weak layer at the base of the snowpack. These locations are generally on Southwest to Northeast aspects and cross-loaded features. Overnight winds will have added some complexity to the distribution of freshly wind-drifted snow at the upper elevations. This drifted snow may overload weak layers allowing for human-triggering a persistent slab on a wider distribution of aspects. 

The new 5-8″ of low density Thanksgiving Storm snow has bonded well to previous surfaces and landed “right side up”. IM Snotel reported 0.5″ of SWE in this storm.

The good news is this storm snow has generally not added undue stress to the snowpack and the layer of concern near the ground. Yesterday’s targeted tests on the weak layer of concern (weak basal faceted sugar snow) showed increasing stability, which has been a slow trend since the last loading cycle on 11/13-14. 

However, we are still getting propagation in some tests and that is pointing to the lingering possibility for triggering an avalanche. 

Since 11/16 the combination of unseasonably warm temperatures and settlement within the entire snowpack (approximtely 4” at 3000’) are continuing to increase stability. We have been tracking the basal facets and observed the crystals to be rounding, which is good news.

Whumphing, beyond small localized cololapses, is a red flag for this avalanche problem, along with shooting cracks and recent avalanches. 

Continue to use safe travel protocol in avalanche terrain:

  • SPREAD OUT when ascending.
  • Descend ONE at a time and regroup in identified safe zones.
  • Avoid riding above or near cliffs, rocks, gullies or other hazards.
  • As always, carry a transceiver, probe, and shovel, and know how to use them!
Avalanche Problem 2
  • 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

Look for freshly drifted snow and wind slabs 2″-5″ thick which will be possible to human-trigger at the upper elevations along ridgelines on leeward aspects. Over the last 24 hours IM Snotel reported westerly winds, which will have transported snow to NE to SE aspects. NWS is calling for early morning winds from the NE. The distribution of this problem may be patchy are hard to predict with a high level of uncertainty.

Wind slabs are often smooth, rounded, and sometimes hollow. Shooting cracks and whumping are red flags for this avalanche problem.

Yesterday we received one report of wind slabs and shooting cracks at upper elevation ridgelines. 

Getting caught and swept in any size avalanche adds the risk of hitting rocks and other hazards which are shallowly buried.

Since 11/25 at 10:00 am the Marmot anemometer appears to have rimed up (icing). This leaves us in a blind spot and creates some uncertainty for upper-elevation ridgeline wind data. However, IM Snotel‘s winds have been reporting. We can estimate that winds aloft were stronger and capable of transporting abundantly available snow for transport.

This hazard should decrease over the next 24 hours.

Avalanche Problem 3
  • Dry Loose
    Dry Loose
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Dry Loose
Dry Loose avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.
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

Thanksgiving’s 5-8″ of new low-density snow will be possible to trigger on slopes 40º and steeper. If you encounter this problem, you probably made a mistake by entering steeper terrain that does not have adequate coverage for riding but will be capable of sluffing. We still need a few more significant storms for the steeper terrain to be ripe.

Weather
Sat, November 26th, 2022

A change in the weather is forecasted for Sunday.  This will bring us sunshine and colder temperatures, however, a pressure gradient is expected to drive strong winds. Strong winds will have the ability to rapidly transport snow, overload our weak snowpack and increase the avalanche hazard.

NWS AVG Forecast here.

NWS point forecast here.

Marmot Weather Station here.

Independence Mine Snotel here.

State Parks Snow Report and Motorized Access information here.

Observations
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