Hatcher Pass Avalanche Center

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ARCHIVED - Forecasts expire after 24 hours.
Issued
Thu, February 22nd, 2024 - 7:00AM
Expires
Fri, February 23rd, 2024 - 7:00AM
Forecaster
Ryan Lewthwaite
Avalanche risk The Bottom Line

All aspects and elevations are rising from MODERATE to CONSIDERABLE avalanche danger as a strong winter storm brings a much needed refresh to the slopes of Hatcher Pass.

Natural avalanches are possible. Human triggering a small to large avalanche will be likely, as 8 to 12 inches of new snow accumulates throughout the day.

Reevaluate the snowpack looking for a dense surface layer and consider terrain less than 35° as the safest option. Expect the avalanche danger to increase as the storm progresses.

The strong winds will begin to decrease this morning, shift southwest, and the rate of snow will intensify bringing heavy snowfall during the daylight hours.

Thu, February 22nd, 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
Fri, February 23rd, 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
Fri, February 23rd, 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
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

It was a warm start to the week with patchy sun and above freezing temperatures in the mid and lower elevations. Strong winds with extreme gusts were recorded at 4500 feet by the Marmot weather station, over the last four days. We observed a cycle of small avalanches from just a few inches of wind blown snow on 2/19-2/20 in the mid and upper elevation zones. Melting snow in the mid and lower elevations caused several small natural wet avalanches.

Natural D1 Wind Slab Avalanche in Lodge Run on Marmot west aspect at 4000 feet 2/20/24

Natural D1 Wet Slab Avalanche on Presidents southeast aspect at 3000 feet 2/20/24

Natural D1 Loose Wet Avalanches on Divide Ridge and Idaho Peak south aspect at 3800 feet 2/20/24

Natural D1 Wind Slab Avalanche near Martin Mine northeast aspect at 3800 feet 2/20/24

Small Natural Avalanche in “Lodge Run” on Marmot Peak West Aspect at 3800 feet 2/20/24

Small Natural Wet Slab Avalanche on Presidents Southeast Aspect at 3000 feet 2/21/24

Small Loose Wet Avalanches on Idaho Peak South Aspect at 3800 feet 2/20/24

Small Natural Wind Slab Avalanche near Martin Mine Northeast Aspect at 3800 feet 2/20/24

Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
  • Aspect/Elevation
  • 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.

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

Expect strong winds to actively transport snow throughout today forming thick and reactive slabs on leeward aspects facing west through northeast in the mid and upper elevations. Blowing snow could make navigating through terrain and avoiding these dangerous slabs very difficult. If we receive the 18-20 inches which are forecasted through Friday, wind slabs could grow up to 12 inches in thickness with continued strong winds and be sensitive to human triggering, with naturals possible.

Use active snow transport as an indicator of where leeward slopes and these slabs may reside. Wind slabs are denser, more rounded in appearance and can be most prominent below ridgelines and cross-loaded terrain features. Cornices could grow significantly throughout this storm and may be brittle and unsupported, with the potential to release naturally. If you encounter cracks shooting from underneath your skis or the whumphing sound of a sudden slab collapse you have found the avalanche problem.

NWS Snow Accumulations for 2/22/24

 

Avalanche Problem 2
  • 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 potent storm has centered over Hatcher Pass with ample moisture and a southeasterly flow. As the strong winds subside this morning and snow falls vertically, expect an even distribution of the new snow. The initial warmth of the storm will help to create a storm slab that is right-side-up with improved bonding to older snow surfaces. In wind protected locations we could see new storm slabs which are 8 to 12 inches thick. These slabs will be most sensitive on slopes over 35° in steepness, especially where terrain changes such as convexities are present. Observe and adjust to the direct feedback of red flags such as shooting cracks, whumphing, and recent avalanches. Storm slabs are typically reactive for a few hours to a couple days. 

In most locations, especially up to 3800 feet, expect snow surfaces prior to the storm to be firm and slick, which could promote larger and easier to trigger avalanches. The warm up over the past week has melted snow surfaces, especially below 3500 feet which have refrozen as a thin and breakable crust. This crust is most apparent in the lower elevation and less pronounced in the mid and upper elevations, where most evenings the overnight temperatures dropped below freezing.

Older firm snow surfaces and windward slopes which have had the snowpack eroded from the landscape are likely areas where you could human trigger a storm slab. These slabs may cover up the wind swept and thinner snowpack areas with fresh new snow so reassessing as you move is highly recommended. 

The initial delivery of the storm has delayed snowfall and allowed strong winds to persist. There is a bit of uncertainty with how this storm is developing. Slabs of wind drifted snow will remain below the anticipated storm slab increasing their sensitivity to human triggering. Expect this storm to persist through Friday, bringing an additional 4 to 6 inches of snow to Hatcher Pass with elevated avalanche danger.  

Heavy rate of snowfall at the 15 Mile DOT Camera at 5AM on 2/22/24

Weather
Thu, February 22nd, 2024

From 2/12 through 2/20 unseasonably warm temperatures plagued our region of Alaska, melting snow and changing the overall condition of our surface snow. Low elevations saw temperatures which reached mid 40F° and even upper elevations including Marmot weather station was reporting 35F° and one evening where did not freeze at 4500 feet. After the temperatures dropped it left behind firm and slick surfaces for new snow to collect on.

Strong Winds Gusting to Extreme at the Marmot weather station at 6AM on 2/22/24

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