Hatcher Pass Avalanche Center

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sat, February 27th, 2021 - 7:00AM
Expires
Sun, February 28th, 2021 - 7:00AM
Forecaster
Allie Barker
The Bottom Line

Today’s avalanche problems are Storm Slab, Persistent Slab and Dry Loose.  Storm slabs 6-8″ thick and Persistent slabs 1-3 feet deep will be possible to trigger at all elevations and all aspects. Small to large dry loose will be possible to trigger at upper elevation on all aspects.

We received approximately 6” of snow overnight and are excepting 2” today with 16″ of new snow since 2/24.

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Sat, February 27th, 2021
Upper Elevation
Above 3,500'
Moderate (2)
Avalanche risk
Mid Elevation
2,500'-3,500'
Moderate (2)
Avalanche risk
Low Elevation
Below 2,500'
Moderate (2)
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
Moderate (2)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Recent Avalanches

Hatcher Pass received approximately 10″ of new snow on 2/24 and 2/25. Natural storm slabs, winds slabs, and dry loose were observed within 24hrs after the storm on all aspects and mostly at mid and upper elevation.

One isolated persistent slab was remotely triggered on 2/25. See OBS here.

 

Skyscraper storm slabs, E 4000′. Look up to the left for the slabs.

 

Marmot W 4000 Wind slabs, dry loose  2.24

 

Punk pines soft slabs NNW 3000′ 2.24

 

Between Nosehairs and Pinnacle, Dry loose WSW 3200′

 

Look in the distance… Pinnacle storm slab, WSW 4800′

 

 

Avalanche Problem 1
  • Storm Slabs
    Storm Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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

Storm slabs approximately 6-8″ thick will be possible to human trigger today on all aspects at all elevations on slopes 35° and steeper. Natural avalanches are unlikely today. We anticipate seeing many natural storm slabs from last night. Newer dense snow over lower density snow will be easy to identify with pole tests and hand shears. Storm slabs instability will improve within 24-48 hours.

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

Persistent slabs, 1-3 feet deep will be possible to human trigger today on all aspects at all elevations on slopes 35° and steeper. We have received 16″ of new snow since 2/24. This snow is sitting on a thin, buried layer of rounded near surface facets. Below this layer, there is a near surface facet layer in the mid pack. Near the base of the snowpack there is depth hoar.  Overall, the snowpack has poor structure with weak layers teetering between dormancy and activity.

In the last storm cycle on 2/24 we received about 1” of water (SWE). Immediately following this moderate load, we saw some small and large natural activity. Most of the natural slab avalanches failed in the mid pack, and a few failed near the ground in isolated locations.

Yesterday and last night’s storm brought a similar amount of water weight (.8-.9” SWE) with only 6″ of snow, due to the warmth of the storm. We should expect to see some similar activity from overnight in the persistent weak-layers near the surface and in the mid pack, and for the potential for a few isolated deeper slabs releases.

Since we are teetering on the balance point and have some level of uncertainty, we recommend starting your day out assessing the new snow load in safe locations before stepping it up into larger pieces of terrain and steeper slopes. If visibility allows, scan the landscape for fresh avalanches and evidence of this problem. Shooting cracks and whumphing are bulls eye clues for this problem. Instability tests on representative slopes, such as the Extended Column Test, should provide good information for propagation potential and today’s risk.

 

 

 

Avalanche Problem 3
  • 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

It will be possible to trigger small to large dry loose sluffs today in terrain steeper than 35º at upper elevation on all aspects. 16” of new snow has accumulated since 2/24, including 6” overnight. Sluffs at upper elevation have the potential to entrain a lot of snow making an exit challenging or taking you somewhere you don’t want to go. This week’s new and mostly dense snow will be challenging to get to move at mid and lower elevations. The good news is sluffs are predictable and avoidable.

 

Weather
Sat, February 27th, 2021

10″ of new snow fell on 2/24-25.

 

 


NWS Rec Forecast here.

NWS point forecast here.

State Parks Snow Report and Motorized Access information here.

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