Hatcher Pass Avalanche Center

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Issued
Sat, March 14th, 2020 - 7:00AM
Expires
Sun, March 15th, 2020 - 7:00AM
Forecaster
HPAC Staff
Avalanche risk The Bottom Line

It will be possible to human trigger or remotely trigger a persistent slab avalanche today at all aspects and all elevations, 1-4 feet deep. Natural avalanches are unlikely. Warmer springtime temperatures today will make it possible to trigger small wet-loose sluffs, on steep slopes, on SE to SW aspects in the afternoon. After a big week of storms, an avalanche fatality, an avalanche that crossed the road, and now bluebird skies…we recommend using heightened avalanche awareness skills, evaluating snow and terrain carefully, and safe travel protocol today.

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Sat, March 14th, 2020
Upper Elevation
Above 3,500'
2 - Moderate
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

A big storm on 3/7- 3/9 deposited about 35″ of new snow and almost 3″ of water at 3550′. This rapid load contributed to an avalanche cycle, mostly occurring mid-storm.

The tragedy of the week was the avalanche accident and fatality on the 16 mile run, on a S aspect at 2000′. This avalanche was a large soft slab on a small slope that funneled into a terrain trap/creek bed. The terrain trap significantly compounded the size of the avalanche. A preliminary report has been done and a complete report will follow.

16 mile avalanche fatality investigation Credit: CNFAIC

Location of the 16 mile avalanche

Location of the human triggered slab avalanche, from higher up on the road run. 3/10

3/9 16 mile avalanche  SS-AR-D2-O

 

Avalanche on Marmot that crossed the road 3/12. We suspect a remote trigger.

Another view of avalanche on Marmot that crossed the road 3/12.

 

 

Avalanche Problem 1
  • 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

Persistent slabs will be possible to human trigger, 1-2 feet deep, on all aspects, and all elevations. 35″ of light density on 3/7-3/9 has settled 15″, increasing the density of the slab. Observers have found this slab to be sitting on a faceted layer. With limited information, we have reason to believe that many of the recent avalanches failed on this upper persistent slab layer.

arrow on the right shows slab avalanche from 3/12. arrow to the left is a new slab triggered during avalanche mitigation on 3/13.

 

 

 

Avalanche Problem 2
  • Deep Persistent Slabs
    Deep Persistent Slabs
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

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

Deep persistent slabs will be possible to trigger today up to 4 feet deep on all aspects and all elevations, most likely on E to W aspects below 3500′. It will be hard to find the “spot” where you can trigger the slab. Remote triggers will continue to be the most likely trigger, and possible from 1/4 mile away. Although many will ski/ride without incident today, this problem is still lingering and we recommend not letting your guard down.

Check out this near miss video from 3/12  here to see how far avalanches are being remotely triggered from.

Below is a video showing poor structure and high propagation of the buried January Facet layer at the 16 mile accident site, S aspect 2000′. This layer will become more of a problem with a significant warm up.

 

Safe travel habits like travelling one at a time, especially on wide open, broad terrain features, utilizing islands of safety, spotting each rider from a safe place, and staying out of the runnout of avalanches from above are all techniques that will increase your safety factor.

Drummy, stiff snow, overlying softer, weak snow is also a good indicator of the problem, however in some cases the weak layer is so deep you probably wont know its there without probing or digging.

Avalanche Problem 3
  • Wet Loose
    Wet Loose
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Wet Loose
Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

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

Spring is here! March is that time of year when the sun shines bright and we start seeing wet avalanche activity, especially after months of deep dark cold. As of 5am it is 21°F at 4500′. It will be possible to human trigger a wet-loose sluff today on steep slopes, in the afternoon, on SE to SW aspects. Pay attention to time of day and stay off slopes if you see rollerballs and signs of significant warming.  If the warming trend continues into the 30’s next week, as forecasted, expect the hazard for wet loose to rise.

Weather
Sat, March 14th, 2020

NWS Rec Forecast here.

NWS point forecast here.

State Parks Snow Report and Motorized Access information here.

Observations
Recent Observations for Hatcher Pass