Hatcher Pass Avalanche Center

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Thu, March 25th, 2021 - 7:00AM
Expires
Fri, March 26th, 2021 - 7:00AM
Forecaster
HPAC Staff
Conditions Summary

Hatcher Pass received 4-5 inches of new snow overnight and are expecting an additional 5-7 inches of snow with moderate to strong winds today. Today’s Avalanche Problems will be Dry Loose, with the potential for Storm Slabs, Persistent slabs and Wind slabs forming throughout the day. Small Dry loose avalanches will be possible on all aspects and all elevations on slopes 40° and steeper. Storm slabs will be found on all aspects and all elevations, human triggered avalanches are possible. Large Persistent Slabs will be possible on East thru West Aspects at all elevations. Small shallow Wind slabs will continue to form near ridge tops at upper elevations on north aspects throughout the day and human triggered avalanches will be possible. 

This storm is forecasted to produce an additional 5-7″ inches of snow by the end of Thursday. Expect avalanche hazards to increase throughout the day as this storm continues. Natural avalanches will be possible as the storm continues throughout the day.

 

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Thu, March 25th, 2021
Recent Avalanches

There were no slab avalanches reported or observed this week. Several dry loose avalanches have been observed this week.

 

Avalanche Problem 1
  • 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

Last night 4-5 inches of snow fell, with an additional 5-7″ of snow forecasted for today. This new snow will be capable of producing small to large Dry Loose avalanches at all elevations, and on all aspects, on slopes 40° or steeper. Human triggered avalanches are possible this morning and natural avalanches will be possible by the afternoon. This snow will likely fail near the sun/drizzle crust and will make for a good bed surface. 

We recommend using good sluff management if you decide to step out into steeper terrain. No matter the size, these avalanches can catch, carry and sweep you through hazards, if not managed properly. 

 

Avalanche Problem 2
  • Storm Slabs
    Storm Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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

Overnight 4-5” of new snow has fallen. Hatcher Pass is expected to receive an additional 5-7” inches of snow by tonight. With increasing temperatures you can expect this new snow to behave like a slab. Storm Slabs will be found on all aspects and all elevations, Small to large human triggered avalanches will be possible on terrain 35° or steeper. Natural avalanches are unlikely. 

Whumping and shooting cracks will be red flags for this avalanche problem Use hand pits, small tests slopes and instability tests to identify Storm Slabs. 

We recommend using low risk travel techniques, this includes spreading out when traveling uphill or near avalanche terrain. Riding slopes one at a time and stopping and regrouping out of harm’s way. Avoid riding slopes that have terrain traps below. Terrain traps can increase your burial depth. An increased burial depth reduces the chance of a successful rescue.

Avalanche Problem 3
  • Persistent Slabs
    Persistent Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    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

4-5” inches of snow fell last night and an additional 5-7″ of snow is forecasted for today. If we do receive this additional snow there is the potential for our persistent slab problem deeper in the snowpack to wake up. This problem will be located on East thru West aspects, at all elevations on slopes 35° or steeper. These avalanches will be large in size and have the potential to fail deeper in the snowpack. If this additional snowfall occurs remote triggering avalanches will be possible.

The snowpack has poor structure made up of multiple weak sugary layers of snow and several crust layers.  See pit here. With this increased rapid load overnight and throughout today, weak sugary snow near the ground is reaching the tipping point. If avalanches fail deeper in the snowpack expect the consequences of being caught and carried to increase.

This problem will be hard to predict. Recent avalanches, whumping, and shooting cracks will be red flags for this avalanche problem. Use ski pole probes to look for stiff snow sitting over weak sugary facets. Use snowpits and hand hardness tests to better identify areas with poor structure. 

Below is a video of the deeper persistent slab problem that has the potential to wake up with the additional load today.

We recommend using low risk travel techniques, this includes spreading out when traveling uphill or near avalanche terrain. Riding slopes one at a time and stopping and regrouping out of harm’s way. Avoid riding slopes that have terrain traps below. Terrain traps can increase your burial depth. An increased burial depth reduces the chance of a successful rescue.

 

Additional Concern
  • Wind Slabs
    Wind Slabs
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.
More info at Avalanche.org

Moderate winds from the S-SW blew for 6 hours. These winds have created small wind slabs in specific areas with slabs averaging 3-5” thick. These are located mid and upper elevations on the north aspects. These wind slabs will be small in size, human triggered avalanches are possible. Natural avalanches are unlikely. Expect this slab thickness to increase if winds continue throughout the day.

Shooting cracks are a red flag for Wind Slabs. Look for smooth freshly drifted snow overlying weak snow when trying to identify this avalanche problem. Pole tests and hand pits will help you quickly identify this avalanche problem

Even a small avalanche could sweep you through rocks or other hazards and cause injuries. 

Use safe travel techniques when traveling in or around avalanche terrain. We recommend spreading out when ascending slopes, descend slopes one at a time, and choose safe zones that are out of harm’s way.

Weather
Thu, March 25th, 2021

3/21-25 New snow totals

Independence Mine:4-5″

Frostbite Bottom: 2-3″

Until this most recent storm we’ve had cold mornings and sunny days! Until the start of this most recent storm Hatcher Pass has calm to light winds with gusts up to 9mph. Temps have been in the single digits near ridge tops at night and upto the mid 20s during the day. At Independence Mine a similar temperature trend has developed as well. Last nights storm brought an increase in temperatures, moderate SSW winds and 4-5″ of new snow.


NWS Rec Forecast here.

NWS point forecast here.

State Parks Snow Report and Motorized Access information here.

Observations
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