Hatcher Pass Avalanche Center

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sat, January 25th, 2020 - 7:00AM
Expires
Sun, January 26th, 2020 - 7:00AM
Forecaster
HPAC Staff
The Bottom Line

Dry loose avalanches (sluffs) will be possible to human trigger on steep slopes, 40° and steeper, at mid and upper elevation, on all aspects, in protected locations. Small, persistent slabs will be possible to human trigger in isolated locations or in extreme terrain, on slopes 35° and steeper, at upper elevation, on all aspects, but mostly likely on loaded and cross-loaded slopes. Steer clear of large cornices that could fall,  increasing the size and/or consequence of an avalanche.

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Sat, January 25th, 2020
Upper Elevation
Above 3,500'
Moderate (2)
Avalanche risk
Mid Elevation
2,500'-3,500'
Moderate (2)
Avalanche risk
Low Elevation
Below 2,500'
Low (1)
Avalanche risk
Upper Elevation
Above 3,500'
Avalanche risk
Moderate (2)
Mid Elevation
2,500'-3,500'
Avalanche risk
Moderate (2)
Low Elevation
Below 2,500'
Avalanche risk
Low (1)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Recent Avalanches

Yesterday we triggered a small persistent slab, 6″ deep by 6 feet wide on a northeasterly upper elevation slope that was cross-loaded. Previous to this, the last avalanche was observed on January 17. See observations.

Small dry loose avalanches (sluffs) have been human triggered in specific areas this week in steep terrain.

1/22/2020 – Southeast, 4500′. Small, human triggered dry loose avalanche. This avalanche started in 2-3″ of new snow, and dredged into old, soft facets, entraining more volume.

 

1/16/2020? – This natural slab avalanche is suspected to have occurred just after the wind loading event on January 15-16. It appears to be approximately 10-12″ deep and small in overall size. Of significant note is its location, which is not at ridgeline where most wind loading occurs. This avalanche shares a pattern of similar avalanches that failed below ridgeline, some mid-slope.

 

The pit below shows all the dry loose snow available as well as the small persistent slab (named wind crust in photo) from Jan15/16. The persistent slab in this picture is 1″ thick but varies in thickness from 6-10″ depending on location. This slab generally lacks propagation.

 

Avalanche Problem 1
  • Dry Loose
    Dry Loose
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    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

A MODERATE Avalanche hazard exists for dry loose avalanches (sluffs) today. Small, dry loose avalanches will be possible to human trigger on all aspects, on slopes 40° and steeper, at mid and upper elevation.  Natural dry loose avalanches are unlikely.

The top foot of the snowpack is highly variable and has low continuity. In many places 2-3″ of new snow (1/21) sits on firm, smooth surfaces. In this situation, it is easy to get a small amount of dry loose snow to slide down steep slopes. In other locations, such as near rock bands and in more wind protected areas, there is up to 1 foot of loose, older, faceted snow. In these areas, it is possible to trigger deeper and larger dry loose avalanches on steep slopes which will have more volume. Expect these avalanches to run fast and be able to knock you down, tweak a knee, or carry you into secondary hazards or terrain traps.  Sluff management and slope cuts are good tools for mitigating this hazard.

Avalanche Problem 2
  • Persistent Slabs
    Persistent Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    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

There is a LOW avalanche hazard for small, 2-10″ thick, persistent slabs today at upper elevation, on all aspects. Natural and human triggered avalanches are unlikely. Any slab avalanches triggered are expected to be small in size, and in isolated areas and/or in extreme terrain. Be cautious above terrain traps, as even a small slab avalanche could wash you into more consequential hazards, such as cliffs and rocks.

The persistent slab problem has steadily increased in stability since last week. We are now approximately 10 days out from the Jan 15-16 natural slab avalanche cycle. PIT. The last observed human triggered slab avalanche, was yesterday and before that, January 16/17. See observations. Yesterday we were able to trigger a very small persistent slab on a cross-loaded feature on a northeasterly aspects at upper elevation. It was small, shallow, 6″ deep, and only 6 feet wide.

The origin of this persistent slab problem came from last week’s strong winds (Jan 15-16) which transported snow and built slabs, generally 2-10″ deep over weak facets, on leeward aspects and on cross-loaded features. Winds were observed to be stronger near the Arkose ridgeline and in areas closer to the boundary of the Matanuska River Valley. During this rapid loading event, numerous natural slab avalanches released. Most were at the upper elevations. We observed a number of slab avalanches near Delia creek and several in the Independence Mine area. Most of these avalanches were shallow, 6″ or less, and a few may have reached 1 foot deep near Delia Creek.

 

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

Due to plentiful snow this season and several periods of strong winds, cornices are large and overhanging in specific areas at upper elevations.

Cornices are difficult to predict the timing of natural release. There have already been a few releases this season involving people and old cornice debris and large chunks are present at the base of some slopes. If traveling under cornices, limit the time of your exposure. If you are approaching cornices from behind, use extreme caution, gain a safe viewpoint to identify safe entries onto slopes below, and do not step out on overhanging cornice features.

Cornice failures may be large, and the mass of a cornice may be large enough to injure or kill a person. Cornices may also entrain more snow and trigger additional avalanche types, which could compound the hazard.

Avoid the cornice which is overhanging the Pinopsicle coulior on the north side of the Pinnacle. This cornice is too large to safely cut or manage. See picture below:

Weather
Sat, January 25th, 2020

NWS Rec Forecast here.

NWS point forecast here.

State Parks Snow Report and Motorized Access information here.

 

HP received 2″ of new snow this week, calm winds, and mostly cold temps in the single digits.

This morning: It’s -4°F at 5am at 3550′ and 0°F at 4500′.

Cold temps will persist through the weekend with a pattern shift on Tuesday bringing clouds and a small chance of precipitation.

Observations
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