Hatcher Pass Avalanche Center
Hatcher Pass

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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sat, March 28th, 2020 - 7:00AM
Expires
Sun, March 29th, 2020 - 7:00AM
Forecaster
HPAC Staff
Avalanche risk The Bottom Line

It will be possible to human trigger a deep persistent slab up to 4′ deep , most likely on East to West aspects, up to 3800′ this weekend. Cooler temperatures have halted the spring warm up and wet avalanches will be unlikely today. Significantly cooler temperatures this weekend will add to the variability of conditions including old firm sun crusts, buried wind crusts, and pockets of powder in protected terrain.  Cornices are large and will continue to be an unpredictable hazard.

UPDATE: Sunday, March 29 at 11 am

Its a good day to “hunker at home.”
A high wind warning has been issued for the Mat Valley 4am Sunday through 1pm Monday. Winds at 4500′ on Marmot are currently ENE 16-23 G 34-51 mph. Expect winds to transport available snow, building wind slabs up to 12″ thick on SW to N aspects mostly at mid and upper elevation.

Special Announcements

For travel or no travel advice this weekend, please refer to the Covid19 Alaska Mandate effective March 28 at 8am “Health Mandate 012 – Intrastate Travel – Limiting travel between communities to critical infrastructure or critical personal needs.”

Check out DHSS COVID19 site for up to date information.   The State recommends sheltering in place. Social distancing and safe travel protocol are ESSENTIAL if you are recreating in Hatcher Pass State Park. DNR message here.

CDC Guidelines –  Read the guidelines HERE.

If you are considering heading towards to Turnagain today, please check the status of the Chugach Avalanche Center and heed their travel advice.

Sat, March 28th, 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 rapid load of 10″ of new snow last Saturday 3/21 reawakened the deep persistent slab problem that has been intermittent for the last month.

On Monday 3/23, another D2 large persistent slab avalanche was observed and believed to be remotely triggered. Look closely and youll see a sympathitic avalanche adjacent to the slope.  NE, E aspect 3500′.

Avalanche between Frostbite and Government 3/23, likely remotely triggered.

A D2.5 large avalanche was remotely triggered by a skier near Delia Creek on Sunday 3/22. This avalanche sympathetically triggered another D2. No one was caught or carried.

 

Small to large wet and dry loose sluffs were reported earlier in the week  on all aspects. No reports of accident or injury.

Wet loose 3/26, NW 3000′

 

Avalanche Problem 1
  • 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 up to 4′ deep will be possible but stubborn to trigger today and most likely on East to South to West aspects at low to mid elevation up to 3800′. For the past several weeks we have seen intermittent remotely triggered avalanches, mostly by large loads such as snow machines, failing on this early January facets weak layer. After 10″ of new snow last Saturday, we observed large remotely triggered avalanches by skiers on Sunday 3/22 and Monday 3/23, all failing on this same layer. We are not out of the woods yet.

Deep persistent slab problems, such as the one we are currently dealing with, are notorious for wavering between periods of dormancy and activity. Let’s not think we are always making good decisions when sometimes we are just lucky. Stay safe out there

We expect cooler temps this weekend to lock up the upper part of the snowpack, making it more challenging to effectively trigger the deep weaker layer. This means that in the short term we may see an increase in stability. For the long term we expect to see a decrease in stability and more avalanche activity as spring-time temperatures rise. 

HS 155cm with 65 cm of facets at the bottom of the pack

Additional Concern
  • Cornice
    Cornice
Cornice
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
More info at Avalanche.org

Cornices remain large and a hazard. Although cornices are known to be unpredictable, we can expect more cornice failure as days lengthen and temperatures increase. Please give cornices a wide berth and reduce exposure underneath on up tracks or adjacent terrain. It will be possible for cornice fall to trigger the deep persistent slab, increasing the size and consequence of any avalanche. This hazard will be on the forefront of our decision making as we move into warmer days ahead.

Weather
Sat, March 28th, 2020

NWS Rec Forecast here.

NWS point forecast here.

State Parks Snow Report and Motorized Access information here.

The Hatcher Pass Mountain Forecast covers the mountains in the
Hatcher Pass Recreation Area.

This forecast is for use in snow safety activities and emergency
management.

                   Today        Tonight

Temp at 1000`      27 F         6 F

Temp at 3000`      9-16 F       0-16 F

Chance of precip   50%          0%

Precip amount
(above 1000 FT)    0.04 in      0.00 in

Snow amount
(above 1000 FT)    trace        0 in

Snow level         sea level    sea level

Wind 3000` ridges  S 1-8 mph    E 1-31 mph

 

Observations
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