Hatcher Pass Avalanche Center
Hatcher Pass

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Issued
Sat, January 23rd, 2021 - 7:00AM
Expires
Sun, January 24th, 2021 - 7:00AM
Forecaster
Allie Barker
Avalanche risk The Bottom Line

Today’s avalanche problems are wind slab and dry loose.

Small, soft wind slabs will be possible to trigger at upper elevations on leeward aspects.  Moderate gusting winds this morning are forecasted through the day which will increase this hazard toward the afternoon.

Small dry loose avalanches (sluffs) will be possible to trigger on all aspects on slopes 40° and steeper.

Continue to practice safe travel habits: one at a time across the slope, get out of the way at the bottom, make a plan.

6″ of new snow this week has improved riding conditions, although a generally shallow snowpack and rock hazards still exist.

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Sat, January 23rd, 2021
Upper Elevation
Above 3,500'
2 - Moderate
Avalanche risk
Mid Elevation
2,500'-3,500'
1 - Low
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

There were three human triggered avalanches this week.

On Thursday, 1/21 a small dry loose (sluff) was human triggered on Presidents. See pic below. This was a slow moving sluff.

On Monday 1/18, two small human triggered wind slabs were reported on lower thousand dollar run, North 3000′. Click here for more info.

On Tuesday 1/19,  a small human triggered soft slab was observed on Presidents Ridge, ENE 2800′. Click here for more info.

Slow moving small sluff on Presidents. 1/21

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

Small, 1-4″ soft wind slab avalanches will be possible to human trigger at the upper elevations, near ridgeline, on leeward aspects. By the end of day the thickness of wind slabs may reach 3-6″.

Shooting cracks are a red flag for this problem. To identify this avalanche problem, look for smooth, drifted snow and firmer snow overlying weaker snow.  Pole tests and hand pits can quickly identify this problem. Proper slope cuts can be an effective tool for mitigating this hazard, but requires skill.

Overnight winds were ESE/E which will have distributed small wind slabs on W to NW aspects. Winds are forecasted to gust at moderate speeds through today which will continue to transport snow and slowly build these soft wind slabs.

A change in the wind direction may occur, which could broaden the distribution of this problem. Today’s wind direction may shift to NE, which would transport available snow and build small wind slabs on South to West aspects.

A highly variable snow depth means rocks and hazards are exposed in many locations. These hazards compound the risk of triggering any avalanche if caught and carried.

Avalanche Problem 2
  • 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

Small, loose dry avalanches (sluffs) are possible on all aspects and at all elevations, on slopes 40° and steeper.

New low density snow from 1/20 has been settling with warm temperatures. This will make sluffs more difficult to trigger than a couple days ago, but is still possible in steeper terrain. See picture of loose dry avalanche under recent avalanches.

Weather
Sat, January 23rd, 2021

New snow totals 1/17-21

Independence Mine: 6″ of new snow

3000′ temps expected to be hovering around freezing. Winds are gusting moderate this morning at the upper elevations and expected to continue through the day tapering off this evening. A shift in wind direction is possible to day, from East this morning to NE this afternoon.

A 30% chance of snow today with little to no accumulation. Snow is forecasted for low elevation, but could be a rain mix if temps climb. Tonight 1-3″ of snow is expected at all elevations.

Marmot 4500′ 24 hr winds

Independence Mine

NWS Rec Forecast here.

NWS point forecast here.

State Parks Snow Report and Motorized Access information here.

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