Hatcher Pass Avalanche Center

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sat, January 11th, 2020 - 7:00AM
Expires
Sun, January 12th, 2020 - 7:00AM
Forecaster
HPAC Staff
The Bottom Line

Today a Moderate Hazard for Small Wind Slabs exists at the upper elevation, on leeward, South to West aspects, on slope 35° and steeper.

A Low Hazard exists for Dry Loose Avalanches at all elevations, on all aspects, on slopes 40° and steeper. Be cautious around loose dry avalanches which could wash or carry you, into terrain traps, compounding the hazard.

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Sat, January 11th, 2020
Upper Elevation
Above 3,500'
Moderate (2)
Avalanche risk
Mid Elevation
2,500'-3,500'
Low (1)
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
Low (1)
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

The last observed avalanches were on January 4.

Pinnacle peak avalanche observation here.

1/4/2020 – Human triggered persistent slab avalanche, 1 foot deep, on Pinnacle peak, Northwest, 5100′. Relatively small slab avalanche, but with serious secondary consequences if caught, since the avalanche ran over a cliff.

 

1/4/2020 – Human triggered persistent slab avalanche on Far Side Variation, Northwest, 4700′. Also a relatively small slab avalanche, but large enough to injure a person.

The last natural avalanches occurred on New Years. Pictured below is an example of the avalanches that naturally released during and just after the new years storm.

Microdot, North, 4800′. New Years avalanche cycle. Numerous slopes were wind loaded and failed naturally.

 

 

Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
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

Triggering a small, soft slab avalanche, 3-8″ deep, will be possible today in specific terrain, on leeward, South to West aspects, at upper elevation.

While strong winds have persisted in Palmer and Wasilla and the Matanuska Valley over the last two days, Hatcher Pass winds have remained calm to light up until last night. Winds overnight at the Marmot weather station (4500′) produced peak gusts for a short period of time, 15-29 mph, for 5 hours. Winds have settled down this morning and are expected to remain light, NE 6-12 mph through the day.

East Northeast winds overnight have transported available low density snow and deposited fresh wind drifted, cohesive slabs on leeward aspects.  These slabs are sitting on persistent, faceted, weak snow grains. Slabs may release above you and propagate further than expected due to the faceted, weak layer problem. Visual clues, such as smooth snow pillows may assist in identifying problem areas. Pole, or probe testing, will also help you to identify an upside down snowpack, where stiffer snow sits over weaker snow. Cracking and collapsing are bulls eye clues for this avalanche problem.

Yesterday’s winds were calm for most of Hatcher Pass, however, strong winds in the Matanuska Valley may have affected the southeastern boarder of Hatcher Pass. Some wind flagging was observed along the Arkose ridgeline. If you venture into this area today, anticipate this avalanche problem to be more severe until proven otherwise. This means slabs may be easier to trigger and may be bigger than what we see in the core portion of our forecast area today.

Wind loading yesterday in the Matauska Valley.

If the winds continue to remain light, expect this hazard to slowly improve through the weekend.

Avalanche Problem 2
  • Dry Loose
    Dry Loose
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
Dry Loose
Dry Loose avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.

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

Small loose dry avalanches will be possible to human trigger, on any aspect, on slopes 40° and steeper. Approximately 6″ of loose snow sits on firm, smooth surfaces. While these types of avalanches may not be large enough to injure you, they may have enough volume to catch you and wash or drag you into terrain traps, such as rocks and cliffs, which will compound the hazard.

Ski cutting can be a safe and effective technique for mitigating this hazard, if properly executed.

Additional Concern
Dry Loose
Dry Loose avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.
More info at Avalanche.org

Glide Avalanches

The last observed glide avalanche release that we know about was on December 7 on the southeast face of Hatch Peak. This activity is a month old, and seems to be in dormancy. However, glide cracks are still present and could release at any time. Many glides are now barely visible from this week’s new snow. Caution should be taken to not ski/ride into these terrain traps. It’s important to note that glide releases can happen in warm or cold weather, are not temperature dependent, and predictability is next to impossible. Any glide avalanche will be large and capable of burying, injuring, and/or killing a person. We recommend avoiding being on or under any locations with glide cracks.

Cornices

Due to plentiful snow this season and strong wind events, cornices are overhanging and large. Cornices are difficult to predict the timing of natural release. There have already been a few releases this season involving people and old cornice debris and large chunks are present at the base of some slopes. If traveling under cornices, limit the time of 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. Cornices may also entrain more loose snow, which could carry you into additional hazards.

Weather
Sat, January 11th, 2020

It’s been awhile since we’ve seen an entire week of below zero and single digit temps! Temps averaged -1.3ºF at 3550′ with a low of -9ºF.

Temps averaged -1ºF at 4500′ with a low of -8ºF.

Cold temperatures are in the forecast through the weekend and into next week.

A strong pressure gradient has been driving outflow winds through the Matanuska Valley for a couple days, and this will persist today and through the weekend.

A low pressure system moving into Southcentral on Sunday will bring a change with some clouds. The pressure gradient between this incoming system and the high pressure firmly entrenched inland will continue to produce the Matanuska Valley strong outflow winds which may effect Hatcher Pass. The incoming low pressure system is not expected to bring much snow, with perhaps an inch or two od accumulation on Sunday.


NWS Rec Forecast here.

NWS point forecast here.

State Parks Snow Report and Motorized Access information here.

 

 

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