Hatcher Pass Avalanche Center
Hatcher Pass

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Issued
Thu, March 18th, 2021 - 7:00AM
Expires
Fri, March 19th, 2021 - 7:00AM
Forecaster
Jake Kayes
Conditions Summary

Today’s avalanche problems will be Persistent slab and Dry Loose. It will be possible for humans to trigger small to large Persistent Slabs at all elevations on East thru West aspects on slopes steeper than 35° degrees. Small Dry Loose avalanches will be possible at all elevations and all aspects. Natural avalanches are unlikely. 

On 3/13 there was a large persistent slab avalanche triggered on the sunny side of Hatch Peak. Avalanches of any size are especially dangerous above terrain traps. Terrain traps increase the chances of a traumatic injury and can also increase your burial depth.

Riding conditions have improved and the drizzle crust has become supportable in some areas. Expect the sun/drizzle crust to more prominent near ridge tops and on south facing slopes.

Special Announcements

Hatcher Pass Avalanche Center is running a special online auction for a one-day stand-by heli seat with Chugach Powder Guides. Over the next FOUR DAYS  you have the chance to show just how much you like HPAC forecasts and heli access skiing or boarding!

Here’s how it works. Visit the “Auction” album on HPAC’s Facebook page between now and March 21, 2021 and place your first bid on the item. The bidding starts at $500. You can increase the bids in whole dollar increments. Check the page regularly and increase your bid if someone has outbid you. The auction will close on March 21st at 8 pm. HPAC will contact the winning bidder. Serious bidders only please.

Recent Avalanches

3/16 Dog triggered avalanche SE aspect 4500’ click here for more info.

3/13 Sunnyside Hatch Peak, SSW 3500’ click here for more info. More photos here.

3/13 Powder Pimple, Hatch Peak, S 3500’ Possible remote trigger

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

Human triggered Persistent Slabs up to 12” thick will be possible on East thru West aspects at all elevations. This problem will be more prevalent on south aspects (SE,S,SW)that have a slab sitting on top of facets on a sun crust/drizzle crust. On many southerly aspects, stout sun crusts combined with the drizzle crust have been found up to 2” thick. Recent cold temps have formed weak sugary snow which is sitting on top of and beneath these crusts. In terms of weak layers, crust-facet sandwiches are often more dangerous than faceted weak layers by themselves. This combination was responsible for the human triggered avalanche on the sunny side of Hatch Peak.

In Isolated areas a cohesive slab has formed and is sitting on top of this crust-facet sandwich. In these locations it will be possible to trigger a Persistent slab avalanche. This cohesive slab is an important ingredient for the Persistent Slab problem, areas that lack slabs will be less likely to slide. This is why we have had a large number of users traveling in steep terrain, but only three human triggered avalanches since 3/12 

Shooting cracks and whumping are red flags for this avalanche problem. Use pole tests and hand pits to help you identify this avalanche problem. Previous tracks on the slope will NOT be an indicator of stability for this avalanche problem. 

Remote triggering this avalanche problem is possible. 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.

Black X is where this avalanche was triggered. Red lines represent the crown for this avalanche. Notice how far down the gulley the crown extends.

Sun Crusts are exposed near some ridge tops.

Sunny side of Hatch Peak before the avalanche.

After

Avalanche Problem 2
  • Dry Loose
    Dry Loose
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    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

Cold temperatures have allowed the surface snow to remain sugary and low density. This low density snow is capable of producing small dry loose avalanches at all elevations and on all aspects on slopes 40° or steeper. Human triggered avalanches are possible, natural avalanches are unlikely. 

We recommend using good sluff management if you decide to step out into steeper terrain. These avalanches will be small but can catch, carry and sweep you through hazards, if not managed properly.

Human triggered dry loose, 4200′ NE.

Weather
Thu, March 18th, 2021

The week started out with temperatures in the teens and light winds from the NW at Independence Mine. At the same time ridgetops were in the single digits with light winds from the WNW. In the afternoon on 3/15 temperatures began to drop into the single digits in valleys and at ridgetops. These cold temps have allowed surfaces to facet and have prevented new sun crusts from forming on the surface. Winds have been light this week.

NWS Rec Forecast here.

NWS point forecast here.

State Parks Snow Report and Motorized Access information here.

Marmot 3/14-3/18:

Independence Mine 3/14-3/18:

 

Observations
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