Hatcher Pass Avalanche Center
Hatcher Pass

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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sat, February 1st, 2020 - 7:00AM
Expires
Sun, February 2nd, 2020 - 7:00AM
Forecaster
HPAC Staff
Avalanche risk The Bottom Line

Persistent slabs, 2-12″ thick are sitting on weak layers and will be possible to human trigger today on all aspects, but most likely on SE to N aspects, at mid to upper elevations, on slopes 35º and steeper. Hard slabs will be difficult to predict and may allow you to step out onto them before failing above you, making escape difficult.

At low elevation it may be possible to trigger small slab avalanches in isolated areas or in extreme terrain.

Special Announcements

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Sat, February 1st, 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'
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

Dry loose sluffs were observed earlier in the week prior to the wind storm beginning January 27th. See obs.

The mighty Matanuska winds blew Jan 27-30, E/ESE/ENE max 39 mph, max gust 52 mph. Winds transported available low density snow, building sensitive wind slabs on SE to N aspects at mid and upper elevation. Natural and human triggered avalanches were observed during and after the wind event. Soft and hard slab avalanches varied from 2-12″ deep, mostly D1, with some up to D1.5 in size. Observers reported shooting cracks and whumping from January 27th to the 31st.

 

Granite Mountain, Tailings Pile, ESE, 3900′ – Human triggered slab avalanche, 5 inches deep, 40 feet wide, ran 150 feet.

 

Above: Small human triggered slabs 1/30. ESE 3900′. More pics here. 

 

Above: Shooting Cracks , SE aspect 4300′. 1/30

 

 

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

A moderate avalanche hazard exists for persistent slab avalanches 2-12″ deep, on all aspects, predominately SE to N aspects, at mid to upper elevations. Natural slab avalanches are unlikely, but human triggered slab avalanches will be possible. It will be more likely to trigger slabs on slopes 35° and steeper, and will require finding just the right spot to trigger a release.

Slab thickness varies from 2-12” thick. The thickest slabs exist on West to North aspects, at upper elevation ridgelines, and cross-loaded slopes, where strong ESE/SE winds on January 27-30 transported available low density snow, forming dense slabs.

Slabs will vary from hard to soft. In the case of hard slabs, they may fail well above you, making escape difficult to impossible. Slope cutting is not a safe technique for mitigating hard slabs. Keep in mind that triggering even a small, shallow slab could sweep you into secondary hazards, compounding the risk.

Shooting cracks, whumphing, and recent avalanches are all red flags, and bulls-eye clues for problem areas to avoid. Probe testing and quick hand pits will identify the presence of this avalanche structure, with firm snow overlying the weaker, softer January High Pressure Faceted snow.

 

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

Due to plentiful snow this season and recent strong winds on January 27-30th, cornices are large, overhanging, and potentially unstable in specific areas at upper elevations, generally, but not limited to, West to North aspects.

Cornices are difficult to predict the timing of a natural release. There have been several releases this season involving people and old cornice debris has been observed at the base of some slopes. If traveling under cornices, limit your exposure. If you are approaching cornices from behind, use extreme caution, gain a safe viewpoint to identify safe entries onto slopes below, and do not step out on overhanging cornice features.

Cornice failures may be large, and the mass of a cornice may be large enough to injure or kill a person, or trigger additional avalanche problems.

Weather
Sat, February 1st, 2020

A trace to 1 ” of new snow was recorded overnight around 3500-4000′.

Clearing skies are expected today and through tonight as the low pressure system in the Gulf of AK, that brought a few snow flakes to South Central yesterday, moves eastward. This will be followed by a large Aleutian low pressure system affecting our region from the west, which should bring clouds and a chance for light precipitation beginning Sunday morning.

Temps at 5000´ today are expected to hover around 0°F, dipping down to -5 to -10°F tonight. Tomorrow temps should begin to rise with incoming weather and clouds, rising into the teens by Sunday evening. Winds are forecasted to remain calm to light with variable direction today, and then shifting to northerly overnight.

The next round of precipitation forecasted for Tuesday and Wednesday do not appear to be major producers. At this point we see the potential for a few inches of snow out of this storm system.

NWS Rec Forecast here.

NWS point forecast here.

State Parks Snow Report and Motorized Access information here.

 

Observations
Recent Observations for Hatcher Pass