Hatcher Pass Avalanche Center
Hatcher Pass

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ARCHIVED - Forecasts expire after 24 hours.
Issued
Fri, April 12th, 2024 - 7:00AM
Expires
Sat, April 13th, 2024 - 7:00AM
Forecaster
Allie Barker
Avalanche risk The Bottom Line

The avalanche hazard is CONSIDERABLE for STORM SLABS and PERSISTENT SLABS at all elevations.

Strong winds prior to the storm combined with 13″ of new snow and another 6-8″ forecasted today will contribute to elevated danger for the next 24-48 hours.

Today marks the 3rd major April storm which has brought ample snow with new avalanche problems to Hatcher Pass.

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

Use careful snowpack evaluation, cautious route finding and conservative decision making to stay safe in avalanche terrain this weekend.

 

Special Announcements

Did you know HPAC is a non-profit, non-agency grassroots avalanche center? We depend on grants and community support to run the center. Your donations help provide Thursday and Saturday forecasts. In the past 12 days we have provided 7 forecasts with numerous additional observations and social media posts. Although spring is here, winter is not slowing down and we need your support and donations to continue providing additional lifesaving avalanche information.
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Regular forecasts will end Saturday April 13th with one additional forecast Saturday April 20th along with a “Spring Outlook.” While there is still skiing and riding to be done, we will continue providing and publishing observations so keep them coming!

Fri, April 12th, 2024
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
Sat, April 13th, 2024
Upper Elevation
Above 3,500'
3 - Considerable
Avalanche risk
Mid Elevation
2,500'-3,500'
2 - Moderate
Avalanche risk
Low Elevation
Below 2,500'
2 - Moderate
Avalanche risk
Sat, April 13th, 2024
Upper Elevation
Above 3,500'
3 - Considerable
Avalanche risk
Mid Elevation
2,500'-3,500'
2 - Moderate
Avalanche risk
Low Elevation
Below 2,500'
2 - Moderate
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

No recent avalanches have been observed or reported due to stormy conditions. Forecasters will assess conditions and stability in the field Friday.

Avalanche Problem 1
  • Storm Slabs
    Storm Slabs
  • Aspect/Elevation
  • 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.
Aspect/Elevation of the Avalanche Problem
Specialists develop a graphic representation of the potential distribution of a particular avalanche problem across the topography. This aspect/elevation rose is used to indicate where the particular avalanche problem is thought to exist on all elevation aspects. Areas where the avalanche problem is thought to exist are colored grey, and it is less likely to be encountered in areas colored white.
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

As of 6am this morning 13″ of new snow with 0.8″ SWE had been reported at the IM snotel @ 3550′. An additional 6-8″ is expected throughout the day.  Strong southeast winds gusted for 12 hrs 33-43mph on Marmot @ 4500′ and 35-49 mph on Hatch @ 4561′ and have slightly tapered this morning as snowfall continues to accumulate.

It will be likely to human trigger slabs up to 12″ thick and potentially growing in size throughout the day. Storm slabs will be likely on all aspects, at all elevations on slopes 35º and steeper. Natural avalanches are possible.

Expect slabs to be thicker on leeward aspects, West to North (clockwise) at mid and upper elevation where winds built slabs over the past 12 hours.

To identify this avalanche problem use formal stability tests and hand pits to see if the new snow is behaving like a slab.  Shooting cracks and whumping will be a red flag for this avalanche problem.  Storm and wind slabs are typically reactive for a few hours to a couple days after a storm.

Marmot weather station at 4500′

 

Hatch weather station at 4561′

Avalanche Problem 2
  • Persistent Slabs
    Persistent Slabs
  • Aspect/Elevation
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    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.
Aspect/Elevation of the Avalanche Problem
Specialists develop a graphic representation of the potential distribution of a particular avalanche problem across the topography. This aspect/elevation rose is used to indicate where the particular avalanche problem is thought to exist on all elevation aspects. Areas where the avalanche problem is thought to exist are colored grey, and it is less likely to be encountered in areas colored white.
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 12 to 36 inches thick will be likely to human trigger on all aspects, at all elevations. Natural avalanches are unlikely.

Hatcher Pass has received over 40″ of new snow since 3/31.  Possible locations to trigger a persistent slab include any aspect where more cohesive slabs are sitting over weak sugary snow on firm crusts.  The good news is the continuity of the weak layer does not exist everywhere so finding a slab/weak layer combo will be challenging and less likely. The bad news is if you do find a location where this recipe exists, triggering a large avalanche will be likely.  Shallower spots in the snowpack or areas previously scoured down to old melt freeze crusts by the wind prior to the last two storms will be more likely locations to trigger a slab.

Remotely triggered avalanches will be possible from below, above, or adjacent to slopes.  This type of avalanche problem often gives unreliable feedback.  Cracking and whumping may or may not occur prior to triggering an avalanche. Pole/probe tests and formal stability tests will help you identify stiffer snow over weaker snow and where this problem exists.

Marmot snowstake at 6am and nearly at the 6′ mark!

 

Weather
Fri, April 12th, 2024

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