Persistent weak layer overview

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This document describes the purpose and use of persistent weak layers (PWL) in the InfoEx system.


An in depth understanding of the current condition of PWLs is critical for avalanche forecasting. InfoEx provides tools for submitting relevant observations, keeping track of the condition of PWLs in your local area(s) and efficiently exchanging this information. The following sections provide a brief overview of the PWL functionality in InfoEx.

Managing PWLs

In comparison to the old InfoEx, where PWLs were simply referred to by a burial date, the new system requires users to explicitly define PWLs. This allows PWLs to be tracked more easily and offers opportunities for advanced queries. The InfoEx system supports two different types of PWLs.

Operation PWLs

Operation PWLs are defined by an operation and represents locally observed PWLs in the snowpack. This allows PWLs to be tracked more easily and offers opportunities for advanced queries. Operation PWLs are managed by operations, which have full control over the characteristics of these PWLs.

See the following documents about managing Operation PWLs:

Community PWLs

Community PWLs is a new concept in the InfoEx system. Since PWLs often exhibit significant spatial variability and might be buried on a range of days, individual operations might create their Operation PWLs differently. Community PWLs provide a mechanism for linking operation controlled Operation PWLs that relate to the same PWL in nature. This grouping of Operation PWLs allows for more meaningful queries in the InfoEx. For example, the community PWL functionality will allow users to more efficiently get a comprehensive picture on the assessments of a PWL that covers a large area and effectively visualize the associated observed avalanche activity.

See the following documents about managing Community PWLs:

NOTE At this point any user with Submission Moderator permissions can manage Community PWLs. However, once the necessary filtering functionality, the idea is that the CAC would be taking the lead in managing the Community PWLs that they are in the best position to assess large scale patterns. However, operators always has the ability to unlink their Operation PWLs from a specific Community PWLs if they disagree with the grouping.

Reporting PWL observation and assessments

The InfoEx system offers a number of options for highlighting PWL-relevant observation and assessing the local condition of their Operation PWLs.

Tagging observations with Operation PWLs

To highlight relevant observations, InfoEx users can tag observations of the following types with Operation PWLs:

  • Avalanche Observations
    Avalanche observations can be tagged with a single Operation PWL under the failure plane section of the observation entry form to indicate the failure plane of the avalanche.
  • Snowpack Observations
    Snowpack observations can be tagged with multiple Operation PWL under the observation details section of the observation entry form to indicate which PWL have been observed in the reported observation.

Assessing Operation PWLs

InfoEx users can track the condition of Operation PWLs and indicate how they relate to the current avalanche problems using the functionality of the following workflow modules:

  • Snowpack module
    The snowpack workflow module allows users to keep track of the current conditions of their Operation PWLs in their region(s). Click here for more information on the functionality of this workflow module.
  • Hazard assessment module
    The hazard assessment module allows users to identify and characterize the present avalanche problems and associate them with Operation PWLs if necessary. Click here for more information on the functionality of this workflow module.

Viewing PWL information

Information on PWLs is presented in the following tables of the InfoEx reports:

  • Avalanche Observations
    The PWL column shows which Operation PWLs have been identified as the failure planes of the reported avalanches.
  • Avalanche Problem
    The Failure Plane column indicates which Operation PWLs have been linked to existing avalanche problems in the Hazard assessment module for the given location.
  • Avalanche Hazard
    The Av Problems column lists the avalanche problems contributing to the current avalanche hazard recorded in the Hazard assessment module for the given location. Problems associated with PWLs have the name of the Operation PWL attached to the avalanche problem label in brackets.
  • Snowpack Description
    The PWL column lists the Operation PWLs currently being tracked in the Snowpack module for the given location.
  • Persistent Weak Layers
    This table presents the PWL assessments completed in the Snowpack module. The '(O)' addition to the PWL name in the PWL column indicates that the label is a Operation PWL and not a Community PWL.

To make it easier and more efficient for users to scan the InfoEx report with respect to PWLs, we are intending to add a avalanche problem/PWL filter functionality to the InfoEx. This would allow you to create a report that would only include observations and assessment related to a specific avalanche problem and/or PWL.

NOTE The avalanche problem/PWL filtering functionality for taking taking full advantage of PWL information the InfoEx report has not been implemented yet!

Related documents

Operation PWLs

Community PWLs

Assessing PWLs

Functionality tested

  • n/a