Hatcher Pass Avalanche Center

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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sat, March 11th, 2023 - 7:00AM
Expires
Sun, March 12th, 2023 - 7:00AM
Forecaster
Allie Barker
Avalanche risk The Bottom Line

The avalanche danger is MODERATE for WIND SLABS up to 6″ thick, on SOUTH to WEST aspects, at upper elevation, on slopes 35º and steeper.

The avalanche danger is LOW for PERSISTENT SLABS on all aspects, at all elevations.

Natural avalanches are unlikely.

This week’s rapid warm up, followed by a return to cooler temperatures combined with strong winds has created stout crusts, wind affected snow, and variable conditions in many locations. Low angle and protected terrain will harness the best snow today.

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Sat, March 11th, 2023
Upper Elevation
Above 3,500'
2 - Moderate
Avalanche risk
Mid Elevation
2,500'-3,500'
1 - Low
Avalanche risk
Low Elevation
Below 2,500'
1 - Low
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

The unusual and rapid warm up that occurred earlier in the week, Monday thru Wednesday, resulted in numerous small to large wet loose avalanches and some slab activity.

For more avalanche info see Observations HERE and Thursday forecast HERE.

3.7-8 Arkose Ridge Wet Loose 3600′ SSW

 

3.8? Wet Loose 3000′ SW

3.8 Natural wet loose at the roadcut, entrance to Hatcher Pass 1100′ SSE

 

3.8 Upper Microdot Naturals, Wet Loose 4200′ SW

 

3.8 Microdot Naturals, Wet Loose 4500′ S

 

Avalanche Problem 1
  • 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 up to 6″ thick will be possible to human trigger at upper elevation on south through west aspects, and cross loaded features, on slopes 35º and steeper. Naturals are unlikely.

Expect NE winds to gust in the teens and 20’s mph until mid-day today and then begin to taper.

The good news is that the duration and intensity of yesterday’s wind was less than forecasted. The bad news is there is still a significant amount of low density snow on northerly aspects available for transport.  On Friday, winds were reported gusting ENE 20-33 mph for 16 hours at 4500′. On our tour Friday, winds were visibly stronger on the Arkose ridgeline and south of the forecast zone, closer to the Matanuska Valley as compared to the IM bowl.  Expect wind slabs to be larger and more sensitive at upper elevation up the Gold Mint Valley and the Arkose ridgeline.

Expect wind slabs NOT to bond well to firm, smooth crust bed surfaces that are prevalent on south to west aspects.

3.10 ENE Strong to extreme winds on Punk Spines/Arkose Ridge transporting low density snow 4500′ Friday morning.

 

3.10 Strong winds at ridgetop on Eldorado Bowl 4500′

A visual clue of strong winds and drifting snow is flagging or pluming at ridgelines.

Stiff snow overlying weaker snow will be easy to identify with pole or probe testing. Shooting cracks are a red flag for this problem.

Avalanche Problem 2
  • Persistent Slabs
    Persistent Slabs
  • 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.

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

Natural and human triggered Persistent Slabs will be unlikely today.

The likelihood of triggering a persistent slab has decreased significantly.  The slab/weak layer combo still exists in some locations, mostly leeward aspects where snow surfaces remained cooler after the rapid warming event Monday-Wednesday. Finding a shallow spot to trigger one of these slabs will be challenging but not impossible.

In isolated locations and extreme terrain at upper elevation, it may be possible to trigger a wind slab on a west aspect that steps down into the persistent slab.

This same senario will be highly unlikely on south aspects due to the impenetrable crusts that have essentially locked up the snowpack.

Due to the return of cooler daytime temps, solid freezing temperatures overnight, combined with northerly winds, conditions have once again shifted abruptly. Thursdays shift towards cooler weather has left firm bulletproof, slide for life conditions on steep southerly aspects, and breakable crusts on mellower terrain.

Unless you have ski racing experience on blue ice in the East Coast and/or excellent edging technique, I’d recommend ski crampons for skinning uphill on steep southerly aspects, or just avoid southerly. Expect crusts of all sorts on East through West aspects at all elevations. On Friday, crusts did not soften throughout the day.

Expect this avalanche problem to rear its head later in the season. With so many buried crusts in the snowpack, especially on southerly aspects, we can expect the persistent slab problem to become more reactive with future loading events.

This photo shows the current snowpack structure on south aspects with lots of buried crusts and moist snow from rapid warming this week.

Weather
Sat, March 11th, 2023

ENE winds gusted 20-33 mph for the past 24 hours at 4500′.

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