Hatcher Pass Avalanche Center
Hatcher Pass

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ARCHIVED - Forecasts expire after 24 hours.
Issued
Thu, February 23rd, 2023 - 7:00AM
Expires
Fri, February 24th, 2023 - 7:00AM
Forecaster
Jake Kayes
Avalanche Warning
Issued: February 23, 2023 7:00 am
Travel in avalanche terrain is not recommended. Avoid being on or beneath all steep slopes.
Avalanche risk The Bottom Line

The avalanche danger is MODERATE and will rise to HIGH by the afternoon. 

A significant weather event will affect the forecast area today. 12 to 18 inches of snow is expected with winds from the South with gusts up to 30mph. In the afternoon 1-2 inches of snow an hour is expected. 

Human-triggered Storm Slab avalanches 12 to 18 inches thick are very likely at all elevations and aspects. These avalanches will be large in size. 

Human-triggered Wind slabs 4-8 inches thick are likely on West to North aspects at upper elevations, these avalanches will be small to large in size.

Human-triggered Dry Loose are likely at mid and upper elevations in protected locations, on slopes 40 degrees and steeper. The avalanche will be small to large in size.

Natural avalanches will be LIKELY by the end of the day. 

Thu, February 23rd, 2023
Upper Elevation
Above 3,500'
4 - High
Avalanche risk
Mid Elevation
2,500'-3,500'
4 - High
Avalanche risk
Low Elevation
Below 2,500'
4 - High
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

There were two human-triggered slab avalanches over the weekend. One was on Feb 19th on Upper Stairstep, the second happened on Feb 20th near Lonetree/Delia creek area on Arkose ridge. 

There have also been numerous human-triggered loose dry loose avalanches and natural wet loose avalanches. 

Human Triggered D2 slab avalanche on Feb 19th. Upper Stairstep, West 3700′ Photo Credit Calvin Hall

Small wet loose skyscraper, South aspect 3400′ Feb 20th

Small wet loose, Cable Valley 4500′ Feb 20th

Human triggered dry loose, Upper eldorado bowl 4500′ Feb 20th

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

A large weather event is affecting the forecast area. Currently, the forecast is calling for 12 to 18 inches of snow to fall in Hatcher Pass with 1 to 1.5  inches of SWE expected. A foot of new snow is expected at all elevations with greater snow totals at upper elevations. Temperatures are expected to increase throughout the day.

We expect this new snow to overload existing weak layers in the snowpack.

Expect slabs to be building throughout the day and for human triggered storm slabs avalanches to be very likely by the afternoon. Natural avalanches will be likely by the end of the day.

By the afternoon large storm slabs 12-18 inches thick will be found at all elevations and all aspects. 

We do not expect new storm slabs to bond well to existing snow surfaces and we anticipate slabs failing within two different layers in the snowpack. In some areas, it will be sitting on weak faceted snow that was formed on Feb 19-21st which brought cold, clear, and calm weather to the forecast areas. This new snow will stress crusts buried deeper in the snowpack, which may cause avalanches to occur deeper in the snowpack.

To identify storm slabs use hand pits, small test slopes, and stability tests. Look for new snow that behaves like a cohesive slab. Cracking and collapsing will be red flags for this avalanche problem.

Travel in avalanche terrain is NOT recommended today. Avoid being in avalanche terrain and beneath steep slopes. 

Heavy snowfall at Marmot Snow Stake this morning

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

For the last 8 hours strong winds from the SSE with gusts up to 25mph have affected the forecast area.

Strong southerly winds with gusts up to 30 mph are forecasted today. These winds will continue to build wind slabs 4-8 inches thick on West thru North aspects and found near ridgeline and cross-loaded features. Winds slabs will be forming on weak faceted snow and may able to propagate further than anticipated.

Human-triggered avalanches will be likely and natural avalanches are possible. These avalanches will be small to large in size.

To identify this avalanche problem look for smooth wind drifted snow. Use pole probes, hand pits, and stability to look for dense snow at the surface with low-density snow below. Shooting cracks and collapsing will be red flags for this avalanche problem.

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

Human-triggered dry loose avalanches are likely at all mid and upper elevations in protected locations on slopes 40 degrees and steeper. Dry loose avalanche will be small to large in size. 

The 12-18 inches of new snow will be falling on over 12 inches of low-density faceted snow. This will increase the likelihood of triggering a large dry loose avalanche. 

Triggering any dry loose avalanche will have higher consequences if traveling above a terrain trap. Know what is below you and use proper sluff management. 

Weather
Thu, February 23rd, 2023

From the NWS Avalanche Weather Discussion- “Hatcher Pass will likely be the big winner for snowfall accumulations, where approximately two feet of wet snow is expected. Snowfall rates in the afternoon are expected to be in the one to two inch per hour range before tapering off overnight.”

Snow totals as of 7am:

Frostbite Weather Station: 3 inches of snow, 0.3 inches of SWE

Independence Mine Weather Station: 4 inches of snow, 0.5 inches of SWE

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