Hatcher Pass Avalanche Center

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Mon, April 5th, 2021 - 7:00AM
Expires
Tue, April 6th, 2021 - 7:00AM
Forecaster
Allie Barker
Avalanche Warning
Issued: April 5, 2021 7:00 am
Travel in avalanche terrain is not recommended. Avoid being on or beneath all steep slopes.
The Bottom Line

Tuesday, April 6: The Avalanche Warning has EXPIRED. The next update will  be Thursday morning at 7am.

DOT says the road will be closed for awhile. 


An AVALANCHE WARNING has been extended and is in effect until Tuesday, April 6 at 7am. The Avalanche danger will be HIGH today. Human triggered avalanches are VERY LIKELY and naturals are LIKELY on all aspects, at all elevations.

HP received 11″ inches of new snow with 2″ inches of water and winds gusting 20-40 mph for the past 24 hours.

The persistent weak layer has been easily overloaded by this storm.  Numerous large natural avalanches have been reported at Hatcher Pass yesterday that have hit and covered the road.

The road is CLOSED before Skeetawk and we encourage you not to travel anywhere at Hatcher Pass at this time.

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

Reports of large D3+ natural avalanches that occurred after 2:30 pm on 4/4.

Recent avalanches are currently being investigated.

Avalanche Problem 1
  • 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

Large Persistent slabs, 2′ to 4′ feet deep, will be very likely to human trigger today on all aspects , at all elevations today. Naturals will be likely.

A significant amount of precipitation from yesterday’s storm has destabilized the snowpack resulting in many large natural avalanches yesterday. Moderate to strong winds been consistent from the SSE/SSW/W through late last night.

Winds slab may step down into the Persistent slab.  Persistent slabs may also fail at or near the ground.

Persistent slabs are sitting on a widespread weak sugary faceted layer on top of a widespread sun crust/drizzle crust combo in many locations at Hatcher Pass. Whumping, cracking, collapsing, and recent avalanches are RED FLAGS for this avalanche problem.

This is an unusual set up for Hatcher Pass for April. Unfortunately this problem is not going away. This is not the time to be in the mountains. The Hatcher Pass road is closed. Please do not attempt to go up to Hatcher Pass at this time. DOT and avalanche assessment needs to occur.

 

 

Avalanche Problem 2
  • Wind Slabs
    Wind Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    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 to strong winds from the SE, SW, W, NW have been persistent for 24 hours, forming wind slabs on many aspects at mid and upper elevation. Winds gusted as high as 40mph at 3550′ yesterday. Wind slabs, 6″ to 12″ thick,  will be very likely to human trigger today on NW,N,NE,E, and SE aspects at mid and upper elevation. Naturals will be likely.  Wind slabs will have the potential to step down into the PERSISTENT SLAB and fail 2′ to 4′ deep, increasing the size and consequence of the avalanche.

More information will be gathered over the next few days about recent avalanches.

 

Additional Concern
  • Dry Loose
    Dry Loose
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.
More info at Avalanche.org
Weather
Mon, April 5th, 2021

NWS Rec Forecast here.

NWS point forecast here.

State Parks Snow Report and Motorized Access information here.

Observations
Recent Observations for Hatcher Pass