Hatcher Pass Avalanche Center

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ARCHIVED - Forecasts expire after 24 hours.
Issued
Wed, April 12th, 2023 - 7:00AM
Expires
Thu, April 13th, 2023 - 7:00AM
Forecaster
Allie Barker
Avalanche risk The Bottom Line

Some might call this a Passover Miracle.

Others wish it was spring.

Hatcher Pass has received 21 inches of new snow at 3500′ in the past 24 hours combined with moderate to strong winds and rising temperatures throughout the storm.

The avalanche hazard is CONSIDERABLE for STORM SLABS, WIND SLABS, and LOOSE DRY avalanches.  It will be likely to trigger an avalanche up to 2+ feet thick today.

Natural avalanches are possible. 

Red flags for avalanche danger include recent avalanches, shooting cracks, and whumphing.

Another 6-8″ of new snow is on the radar for today.

Dangerous avalanche conditions exist. Careful snowpack evaluation, cautious route-finding, and conservative decision making will be essential today. 

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Wed, April 12th, 2023
Upper Elevation
Above 3,500'
3 - Considerable
Avalanche risk
Mid Elevation
2,500'-3,500'
3 - Considerable
Avalanche risk
Low Elevation
Below 2,500'
3 - Considerable
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

Due to stormy conditions and zero visibility we have not observed any recent avalanches in the past 24 hours. We expect to see numerous avalanches in the field day.

For observations from earlier in the week click HERE.

Avalanche Problem 1
  • Storm Slabs
    Storm Slabs
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    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 will be likely to human trigger today on all aspects, at all elevations, on slopes steeper than 30º. Natural avalanches are possible.

Expect slabs to be 24+” thick at upper elevation, up to 20″ thick at mid elevation, and up to 12″ thick at low elevation.

It is possible that storm slabs will larger and more reactive on southerly aspects where buried crusts are smooth and firm.

Expect new cohesive storm slabs to feel slightly inverted from rising temperatures throughout the storm, especially below 3500′.  To identify storm slabs use hand pits, small test slopes, and stability tests.  Cracking and collapsing will be red flags for this avalanche problem.

Dumping! Mile 15 web cam at 1am and its still snowing.

 

 

Avalanche Problem 2
  • 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

Wind slabs 6-12″ thick will be likely to tigger on leeward aspects, W to N, at upper elevation, on slopes steeper than 35º. Wind slabs will be possible to trigger at mid elevation and unlikely at low elevation where winds have been relatively calm.

At 4500′, winds have been gusting SE 20-23 mph intermittently over the past 24 hours with consistent gusts in the teens.  Additional new snow accumulation combined with lack of visibility throughout the day will disguise wind slabs that have formed and make identifying them challenging to impossible today.

To identify wind slabs look for hard snow sitting over weaker snow, smooth and rounded or lens shaped features.  They may sound hollow or crack out from your ski tip or snowmachine as you travel across them.  Shooting cracks and whumping are signs of instability and indicators of this avalanche problem.

Expect wind slabs to become less reactive within 24-48 hours after the storm ends.

Wind on Marmot at 4500′ have accompanied new snow with rising temperatures over the past 24 hours.

Avalanche Problem 3
  • 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

Loose dry avalanches (sluffs) will be likely to trigger at all elevations, on all aspects, on slopes steeper than 40º. Expect the volume of sluff to be considerably larger at upper elevation and smaller at low elevation.

Expect sluffs to gain more momentum and run further above 4000′ where cooler temps during the storm combined with lower density snow has accumulated.  Any buried crust or smooth bed surface will contribute to the size and speed of this problem.

Avoid steep slopes above terrain traps. These avalanches will be capable of sweeping you off your feet and carrying you into terrain traps, compounding the hazard.

Weather
Wed, April 12th, 2023

IM @ 3550′ has reported 21″ of new snow with 1.2″ SWE in the past 24 hours (SWE is typically delayed). Frostbite @2700′ has reported 10″ new snow with 0.6″ SWE in the past 24 hours. Winds on Marmot at 4500′ have been SE 12-17 G 17-23 mph over the past 24 hours.

Another 6-8″ of snow is in the forecast for today and will begin to taper by end of the day.

 


NWS AVG Forecast here.

NWS point forecast here.

Marmot Weather Station here.

Independence Mine Snotel here.

Frostbite Bottom Snotel here.

State Parks Snow Report and Motorized Access information here.

XC trail grooming report for Mat-Su, Anchorage, and Kenai here.

Observations
Recent Observations for Hatcher Pass