Hatcher Pass Avalanche Center
Hatcher Pass

Hatcher Pass RSS

Archives
ARCHIVED - Forecasts expire after 24 hours.
Issued
Sat, December 16th, 2023 - 7:00AM
Expires
Sun, December 17th, 2023 - 7:00AM
Forecaster
Allie Barker
Avalanche risk The Bottom Line

9 inches of new snow accumulated over 9 hours which has increased the avalanche danger!

A CONSIDERABLE hazard exists for STORM SLABS on slopes 35º and steeper and DRY LOOSE on slopes 40º and steeper at upper elevation, on all aspects.  A MODERATE hazard exists at mid elevation. A LOW hazard exists at low elevation.  Natural avalanches will be unlikely.

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

Winds are expected to increase Saturday afternoon followed by an additional 12 to 16 inches of snow Saturday evening into Sunday. Expect the avalanche danger to remain elevated.

Special Announcements

During the 2022-23 season, the generous contributions of our community supported 53 forecasts, 25 storm warnings, over 100 forecaster field days, and a growing community education program. Please consider HPAC in your year-end giving. Your donation will directly support our ability to produce more forecasts, grow our team, and continue investing in new projects like the Hatch Peak weather station this year. Donate today!

Sat, December 16th, 2023
Upper Elevation
Above 3,500'
3 - Considerable
Avalanche risk
Mid Elevation
2,500'-3,500'
2 - Moderate
Avalanche risk
Low Elevation
Below 2,500'
1 - Low
Avalanche risk
Sun, December 17th, 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
Sun, December 17th, 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

We expect several natural avalanches to have occurred yesterday that have not been reported.

Earlier in the week, we observed small to medium size human triggered dry loose sluffs. See obs for more info.

12/14 Eldorado Bowl NNE 4500′ Human triggered sluffs

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

A quick and efficient storm deposited an inch an hour for 9 hours yesterday. This is a rapid load that will increase avalanche danger for 24-48 hours.  We expect most of the natural activity to have occurred last evening.

9 inches of new snow with 0.6″ SWE was reported at IM/3550′ and 3-4″ new snow with 0.3″ SWE was reported at Frostbite/2700′.

Expect 6-9″ thick storm slabs to be reactive and fail on weak near surface facets that formed over the past several days with cold temperatures.

Storm slabs will be likely to human trigger at upper elevation and possible to trigger at mid elevation, on all aspects, on slopes steeper than 35º. Natural avalanches are unlikely.

At low elevation where less snow accumulated, storm slabs will be unlikely.

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 slabs are typically reactive for a few hours to a couple days.

12/15 Marmot Lodge snowstake

Winds are forecasted to increase Saturday afternoon followed by another pulse of snow on Sunday. Expect this additional load to keep the avalanche danger elevated for another 24 to 48 hours.

WIND SLAB

SSE winds gusted 26 mph for approximately 8 hours during the storm at 4500 ft. Although the duration was short, a significant amount of low density snow was available for transport. It will be possible to human trigger small 2 to 4 inch thick wind slabs on NW to N aspects at upper elevation, on slopes steeper than 35º.  Natural avalanches will be unlikely.

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 as you travel across them.  Shooting cracks or whumping are signs of instability and indicators of this avalanche problem.

Avalanche Problem 2
  • Dry Loose
    Dry Loose
  • Aspect/Elevation
  • 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.
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

Up to 9 inches of new snow yesterday combined with the previous week’s 10+ inches of snow will increase the likelihood today for triggering a dry loose avalanche (sluff).  Small to large sluffs will be likely to human trigger in steep terrain greater than 40º on all aspects, at upper elevation in protected terrain. Small to medium size sluffs will be possible to human trigger at mid elevation.

Expect new low density storm snow to be sitting on buried near surface facets which will increase the likelihood and speed of any sluff.  In locations with previously firm surfaces, these will be easier to trigger and larger in volume.

Sluffs may be able to sweep you off your feet into or over other rocks and hazards.

Small dry loose avalanches can be mitigated safely with appropriate slope cutting techniques.

 

 

Weather
Sat, December 16th, 2023

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