Hatcher Pass Avalanche Center
Hatcher Pass

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ARCHIVED - Forecasts expire after 24 hours.
Issued
Thu, February 17th, 2022 - 7:00AM
Expires
Fri, February 18th, 2022 - 7:00AM
Forecaster
Allie Barker
Avalanche Warning
Issued: February 17, 2022 7:00 am
Travel in avalanche terrain is not recommended. Avoid being on or beneath all steep slopes.
Avalanche risk The Bottom Line

The Valentines Day Special has turned into a week long storm bringing over 3″ of water and 20″ of snow to Hatcher Pass, so far, and it is still snowing! We are expecting another 12-18″ of snow and 1.7″ SWE (water) thru mid day Friday.

Avalanche danger will remain HIGH today. Large to very large human triggered avalanches are very likely on all aspects at all elevations on slopes above 30º. Naturals avalanches are likely. 

The road will remain closed at mile 11 through the weekend due to avalanche danger.

 

Special Announcements

We are forecasting more than normal because of the Valentines Day Storm. If you value up-to-date life saving information please support our non-profit avalanche center HERE. 

Thu, February 17th, 2022
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

We expect that numerous natural avalanches have occurred since the 14th but due to the road closure and poor weather we are unable to provide any photos of those avalanches. we will assess as soon as the weather tapers and a weather window is available.

Below are a couple photos of slab avalanches at the road cut from Wednesday. These are small avalanches but indicative of a larger problem. Zoom in to see the crowns.

 

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

The weak layers in the snowpack are getting deeper.

1.5 to 4 ft thick persistent slabs will be very likely to human trigger on all aspects, at all elevations today on slopes steeper than 30°. Natural avalanches are likely. It will be possible to remotely trigger large avalanches from adjacent or below slopes.

The problem weak layers are the December 26 crust/sugar facet combo and the November basal, sugary facets. In many cases this season, avalanches have failed on top of the crust, and then stepped down deeper into the weak basal facets. We expect to see both these layers fail in this not so sweet Valentines storm. Shallower southerly aspects will see more avalanche activity.

Any wind will add additional stress to this weak sensitive snowpack. All our anemometers are frozen and not reporting accurate information since the freezing drizzle event on Tuesday. Winds are expected to pick up slightly for the next 12 hours SE 10-26 mph.

4 of the 5 red flags have been present over the last 24 hours. New snow, Recent avalanches, Collapsing/Cracking, and Rise in temperature. We could see it snow up to 2″/hour over the next 12-18 hrs.

We are moving towards a deep slab problem.

Very dangerous avalanche conditions. Travel in avalanche terrain is not recommended.

Avalanche Problem 2
  • 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

12 to 20″ thick Storm Slabs will be very likely to human trigger on all aspects at all elevations on slopes steeper than 35°. Natural avalanches will be likely.

Approximately 20″ of new snow and 3.3″ of water has rapidly accumulated at 3550′ over the since the 14th. Lower elevations have seen less snow but a similar amount of water.

It will be likely for storm slabs to step down into the persistent slab, increasing the size and consequence of an avalanche.

 

Weather
Thu, February 17th, 2022

 

NWS AVG Forecast here.

NWS Rec Forecast here.

NWS point forecast here.

State Parks Snow Report and Motorized Access information here.

Observations
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