Hatcher Pass Avalanche Center

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Thu, March 23rd, 2023 - 7:00AM
Fri, March 24th, 2023 - 7:00AM
Tim Rogers
Avalanche risk The Bottom Line

The avalanche danger is MODERATE at mid and upper elevations for WIND SLAB on SOUTHWEST to NORTHWEST aspects on slopes 35º and steeper. The danger is LOW at low elevation. 

Conditions are variable, with a variety of crusts to be found on most aspects. There are soft turns to be found on sheltered and low angle slopes but the price of admission is high. 

The avalanche danger could rise by the end of the week with snow showers possible throughout the day today and a quick hitting trough expected Friday that could bring 6-12” of snow and a period of strong winds to the area.

Additional snow and loading could create storm slab instabilities, obscure existing wind slabs, and increase the potential to trigger avalanches that fail deeper in the snowpack. Keep an eye on recent accumulations if you’re heading up later this week. New snow will change the game.

Thu, March 23rd, 2023
Upper Elevation
Above 3,500'
2 - Moderate
Avalanche risk
Mid Elevation
2 - Moderate
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

One of the few parties out last weekend was able to trigger a sizeable wind slab that pulled out above them. We investigated this avalanche in upper $1000 run and found it had failed on a smooth firm crust. 

Investigating recent activity on $1000 run. NW facing 4000 ft.

Recent Conditions

Raised tracks, patchy loading and if you look close, an avalanche.

Conditions are variable. Strong easterly winds have taken their toll and left behind raised tracks, patchy windslabs, and a firm crust on solar aspects.

Strong faceting blow the stiff crust on solar aspects.

The crust on solar aspects is firm and encouraging facet growth under it as seen above. Structure on these aspects is poor but wont be a problem until we see significant loading.

Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
  • Certain
    Very Likely
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
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

Strong easterly winds on Friday built stiff wind slabs 2-12’’ deep. Periods of moderate to strong easterly winds continued through the last few days and have distributed a variety of thin wind skins on mid and upper elevation SW through NW facing slopes. 

Wind slabs will appear as smooth lenses or pillows on leeward or cross loaded aspects. They may sound hollow or crack out from your ski tip as you travel across them. 

Wind sculpted terrain found on Skyscraper Ridge.

There are a variety of wind slabs out there to contend with, some are thick, firm, and edgeable, while others are thin, punchy, and grabby. For the most part these slabs are patchy in their distribution due to the overall lack of snow available for transport. On broad or convex slopes these pieces could be more firm, well connected, and easy to trigger.

As with the avalanche we observed yesterday, the possibility exists for these wind slabs to behave more like persistent slabs and break out above you or fail on deeper layers of the snowpack, up to 3′ deep. 

As these slabs age they will become more stubborn and unreactive, meaning they could wait to release until you’ve found a thin spot on the slab. The structure exists for these slabs to fail on facet crust layers deeper in the snowpack, increasing the size and consequence of the avalanche. 

Thu, March 23rd, 2023

Recent winds have contributed to the majority of conditions out there. The graph below shows that after their peak on Sunday, winds continued to gust into the 30’s this week and transport what little snow is left.

After their peak last weekend, winds have continued to gust into the 30’s this week.

It’s currently snowing, with a trace to an inch of new snow expected today and continued light to moderate South/Southeasterly winds.

There looks to be increasing chances for more accumulations Friday with a quick hitting trough that will bring a period of strong snow and wind.

Day 2 QPF Snowfall showing 8-12” on Friday.

With changing conditions be sure to have a look at recent snowfall through the links below.

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.

Recent Observations for Hatcher Pass