Hatcher Pass Avalanche Center

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Thu, March 30th, 2023 - 7:00AM
Expires
Fri, March 31st, 2023 - 7:00AM
Forecaster
Tim Rogers
The Bottom Line

The avalanche hazard is MODERATE for PERSISTENT SLABS at mid and upper elevations on WEST through EAST facing aspects on slopes 35° or steeper. 

A LOW hazard exists on all other slopes and aspects for the same problem. 

Last week’s storm included a few inches of graupel. Because of its size and water content, this snow can persist as a weak layer for some time (more in the problem discussion). In areas where this snow fell on a smooth firm crust, lingering instabilities still exist. Snowpit tests also point to the possibility of triggering an avalanche on a slightly deeper layer just below some of the wind slabs that formed during the previous week. 

Thu, March 30th, 2023
Upper Elevation
Above 3,500'
Moderate (2)
Avalanche risk
Mid Elevation
2,500'-3,500'
Moderate (2)
Avalanche risk
Low Elevation
Below 2,500'
Low (1)
Avalanche risk
Upper Elevation
Above 3,500'
Avalanche risk
Moderate (2)
Mid Elevation
2,500'-3,500'
Avalanche risk
Moderate (2)
Low Elevation
Below 2,500'
Avalanche risk
Low (1)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Recent Avalanches

Overall there were relatively few skiers out and around Hatcher Pass over the weekend, most making conservative terrain choices and sticking to mellow slopes. Despite this fact a couple parties observed some collapsing and a couple small skier triggered slides in the new snow. All this activity was reported in mid and upper elevation northerly facing terrain. 

A small slide observed on the way to Farside on Tuesday. About 4k’ ft NW facing.

A few sunny days and warm temps helped initiate some wet loose activity on steep rocky solar aspects. If the sun comes out even briefly it has some strength. Avoid slopes that are becoming wet or unsupportable. 

 

Conditions Photos

Last week’s snow has settled out and formed a soft but cohesive 6-10’’ slab in most locations.  Skiing and riding is still generally soft and supportable on the north half of the compass. You’re not really feeling the bottom unless you’re on something steeper or where the recent storm snow was scoured away. 

Skiers enjoying smooth turns on Nosebleed.

A few warm sunny days added a thin sun crust on solar aspects and have likely degraded riding conditions on these slopes. 

A party enjoying good visibility in the eastern zone of the forecast area earlier this week.

Avalanche Problem 1
  • Persistent Slabs
    Persistent Slabs
  • Almost 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

Recent snow from Friday included 2-3’’ of graupel. Because of its size and water content this grain easily facets in cooler temperatures and can act as a weak layer for future avalanches. Additionally, this snow fell on a variety of surfaces including some areas of smooth firm crusts where it can act like ball bearings and increase instability. 

Some graupel grains that have undergone metamorphism in both directions but are still showing some sharp edges (facets) on their perimeters.

Expect these avalanches to be 4-12’’ deep and 30-50’ wide and found on mostly northerly facing slopes west through east. While this problem should remain manageable for skiers, it will generally be found mid-slope in gullies, under cliffs, and where consequences of getting caught may be higher. 

Recent skier triggered activity from Saturday below Microdot (see observation).

Snowpit tests also pointed to the possibility of triggering a slightly more deeply buried weak layer under the firm wind slabs that formed during periods of strong easterly winds 3/19 – 3/22. While this situation is less likely, the best course of action is still to follow safe travel protocols and only expose one person at a time if you’re skiing steep, exposed slopes on the north end of the compass. 

Snowpack layering near the surface on upper elevation W/NW facing slope.

Lastly, while not a persistent slab issue, keep an eye out for warming temps and wet loose activity with daytime heating. We should see mostly cloudy skies the rest of this week but with mild temps and a weak refreeze overnight this could still be a possibility. Spring is trying to make a presence and when the sun pokes out, it has some strength to warm the snow quickly.

Weather
Thu, March 30th, 2023

The strongest effect the weather has had on the snowpack over the last few days has been from the sun and mild temperatures. Winds remained light out of the S/SE but mild temps, high humidity, and some strong solar helped settle the recent snow and even dampened the snow surface on S facing slopes. Overall, the nice weather help settle and consolidate the snowpack in a positive direction, and on shady and sheltered slopes the skiing is still cold, soft, and supportable. 

Mild temps through the weekend and some high humidity starting Tuesday helped settle and thicken the recent snow.

It’s currently snowing and an inch or two of snow is expected over the next few days with light to moderate southerly winds and mild temps in the 20’s. Visibility could be tough at times with high clouds and periods of snow showers. 

Inspecting solar affect on the ridgeline with deteriorating visibility on the way.

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
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