Hatcher Pass Avalanche Center

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Thu, March 11th, 2021 - 7:00AM
Expires
Fri, March 12th, 2021 - 7:00AM
Forecaster
Jake Kayes
Conditions Summary

Today’s avalanche problem will be Persistent Slab and Dry Loose. It will be possible for humans to trigger and remotely trigger Persistent Slabs at mid and upper elevations on West thru North aspects on slopes steeper than 35 degrees. Small Dry Loose avalanches will be possible at all elevations and all aspects on steep slopes. Natural avalanches are unlikely. 

Over the last two days Hatcher Pass has received up to 9″ of new snow at 3550′. As the weekend approaches keep in mind any increase in wind speeds or another significant snowfall will increase avalanche danger.

Yesterday there was a small D1.5 remotely triggered avalanche on Marmot. Be aware of steep slopes above and of terrain traps below. Small avalanches can still be dangerous, especially if they sweep you into terrain traps. 

Riding conditions have improved and the drizzle crust has become supportable in some areas.

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 two weeks you have the chance to show just how much you like HPAC forecasts and heli access skiing or boarding!

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Thu, March 11th, 2021
Recent Avalanches

Numerous dry loose and wet loose avalanches were observed Sunday and Monday. On Wednesday three small slab avalanches were triggered on the west face of marmot.

3/10: Marmot West Face 3800’ click here for more info.

Avalanche Problem 1
  • 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

On 3/10 moderate to strong winds from the southeast, combined with 7” of new snow were able to bury weak sugary snow building slabs  4-12” thick and in isolated areas up to 18”. These freshly loaded Persistent slabs will be found at mid and upper elevations, on west thru north aspects. Human triggered avalanches will be possible and natural avalanches are unlikely. 

These freshly loaded slabs are failing on buried near surface facets sitting on  the 2/26-27 Drizzle crust. A couple things to be aware of…crust-facet sandwiches are often more dangerous than facet layers. We believe the drizzle crusts and NSF layer to be widespread which will continue to contribute to this problem with additional loading events. This crust has made for a nice bed surface for these avalanches to fail on. Additionally, it will be possible for humans to remotely trigger this avalanche problem. 

There are several weak sugary layers that are currently buried in the snowpack. First is the drizzle crust facet combo which is 4-12” from the surface. Below this, In the middle of the pack lies an old weak sugary layer of facets. Near the base of the snowpack sits a layer of facets and depth hoar. Click here to gain a better understanding of layering in the snowpack.

Shooting cracks and whumping are red flags for this avalanche problem. Look for smooth freshly drifted snow overlying weak snow when trying to identify this avalanche problem. Last night’s new snow will make visually identifying this problem more challenging. Pole tests and hand pits will help you quickly identify this avalanche problem. 

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.

The drizzle crust has become quite thick in some locations

A small D1 avalanche on Marmot Ridge W 3800′

Avalanche Problem 2
  • Dry Loose
    Dry Loose
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

9” of new snow has fallen this week. 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. 

 

Weather
Thu, March 11th, 2021

3/07-3/11 New Snow Totals:

Independence Mine: 9” of new snow

Frostbite Bottom: 7″ of new snow

The week started off with clear sky and almost spring like conditions. On 3/07 temps started off in the single digits but by March 8th had risen to the high 20s. On the 3/07-3/08 sunny weather and warm temps were able to warm snow surfaces and create Wet Loose problems on steep southern slopes. Late on 3/09 a storm system moved over Hatcher Pass. By the morning of 3/10 moderate to strong winds from the SE blew for 10 hours, these winds were able to transport some snow. The distribution of the 2/26 crust is somewhat variable, thick and supportable in some areas, thin and breakable in others.


NWS Rec Forecast here.

NWS point forecast here.

State Parks Snow Report and Motorized Access information here.


Independence Mine: 3/07-3/11


Marmot: 3/07-3/11


Frostbite Bottom: 3/07-3/11

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