Snow Pack objects contain parameters that characterize the buildup, removal, and melting of snow over three types of sub-areas within a catchment:

• The Plowable snow pack area consists of a user-defined fraction of the total impervious area. It is meant to represent such areas as streets and parking lots where plowing and snow removal can be done.
• The Impervious snow pack area covers the remaining impervious area of a catchment.
• The Pervious snow pack area encompasses the entire pervious area of a catchment.

Each of these three areas is characterized by the following parameters:

• minimum and maximum snow melt coefficients
• minimum air temperature for snow melt to occur
• snow depth above which 100% areal coverage occurs
• initial snow depth
• initial and maximum free water content in the pack.

In addition, a set of snow removal parameters can be assigned to the Plowable area. These parameters consist of the depth at which snow removal begins and the fractions of snow moved onto various other areas.

Catchments are assigned a snow pack object through their Snow Pack property. A single snow pack object can be applied to any number of catchments. Assigning a snow pack to a catchment simply establishes the melt parameters and initial snow conditions for that catchment. Internally, the SWMM solver creates a "physical" snow pack for each catchment, which tracks snow accumulation and melting for that particular catchment based on its snow pack parameters, its amount of pervious and impervious area, and the precipitation history it sees.

The Snow Pack Editor contains a list view for the snow pack's name and two tabbed pages, one for Snow Pack Parameters and one for Snow Removal Parameters.

Access the Snow Pack Editor by selecting Components > SWMM Extensions > Snow Pack, or by selecting Edit in the Snow Pack field in the Properties Editor when viewing the properties of a catchment (note: for the Snow Pack field to be visible, Has Snow Pack? must be set to True).