Hatcher Pass Avalanche Center

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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sat, April 13th, 2019 - 7:00AM
Expires
Sun, April 14th, 2019 - 7:00AM
Forecaster
HPAC Staff
Avalanche risk The Bottom Line

The avalanche danger will be MODERATE today for new winds slabs, 4-6″ thick, on NW to NE aspects, at upper elevation, on slopes steeper than 35º. The avalanche danger today will be LOW in the morning, rising to MODERATE in the afternoon for wet avalanches.  Human triggered avalanches will be possible at low and mid elevations, on steep slopes greater than 40º, on mostly SE to W aspects. Cornice fall will be possible on leeward aspects today.

A solid overnight freeze will make for firm and challenging travel at most elevations in the morning until warmed by the sun and rising afternoon temps. Ski crampons and/or cursing might increase your enjoyment this morning.

Cornices are still large and unpredictable, give them a wide berth. Winter is back, if only for a moment, so get out and enjoy it!

Special Announcements

This is the last avalanche advisory of the season, but for those of you not willing to put the skis away yet, keep those observations coming! Thank you for a great season. If you haven’t had a chance to support your local avy center, please consider DONATING today to help the coffers for next season. Best way to DONATE is directly to HPAC either via Facebook or HERE.  Thank You!

Sat, April 13th, 2019
Upper Elevation
Above 3,500'
2 - Moderate
Avalanche risk
Mid Elevation
2,500'-3,500'
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

Avalanche activity has been kept to a minimum due to a significant cooling trend for most of the week, especially above 3000′. Warm days didn’t get quite warm enough to produce noticeable wet avalanches. Winter returned Friday, bringing up to 4 inches of new snow to HP. Due to poor visibility Friday, no avalanches were observed. It is likely that small natural wet avalanches occurred on Friday before a solid freeze overnight.

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

Moderate wind gusts, SSE 13-21 mph on 4/12 combined with about 4” inches of new snow will make it possible to human trigger a new wind slab today 4-6” thick on NW to NE aspects at upper elevation, on slopes 35º and steeper. New wind slabs will be sitting on old faceted surfaces and will not bond well. Expect small avalanches in specific areas, up to D1 in size. It will be possible in very isolated locations for a small wind slab to initiate a larger dry loose sluff, if you are lucky enough to find the hidden square powder.  Assessing this hazard and good terrain management will be key to avoiding this problem.

Avalanche Problem 2
  • Wet Loose
    Wet Loose
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Wet Loose
Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

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

Strong sunshine today combined with 4” inches of new moist snow (frozen overnight) will make small human triggered wet loose sluffs possible on steep slopes, on mostly SE to W aspects, at low and mid elevation, in the afternoon. Small loose dry sluffs may be possible at upper elevation on solar aspects once the sun hits.

A solid overnight freeze will keep avalanches small and will not be enough to raise your neck hairs over deeper crusts softening and contributing to a larger avalanche problem.

Fortunately, the snowpack gives us clues when the it becomes wet enough to be a problem. Rollerballs, and wet soggy snow are red flags for when to move to shadier aspects and cooler terrain.

Additional Concern
  • Cornice
    Cornice
Cornice
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
More info at Avalanche.org

Cornice failures are unpredictable and a high consequence hazard. We can reduce our exposure to this hazard by limiting time spent under or near this hazard. Avoid uptracks with cornices above. While traveling on ridgelines, cornices may fail further back from the edge of slopes than expected, and may pull out adjoining snow. Cutting cornices is not recommended as a stability testing tool, as the hazards associated with cutting them are greater than the value of the information we may gather.

Weather
Sat, April 13th, 2019

NWS Rec Forecast here.

NWS point forecast here.

State Parks Snow Report and Motorized Access information here.

Observations
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