The Snow Pack Parameters tab of the Snow Pack Editor dialog provides snow melt parameters and initial conditions for snow that accumulates over three different types of areas: the impervious area that is plowable (i.e., subject to snow removal), the remaining impervious area, and the entire pervious area. The page contains a data entry grid which has a column for each type of area and a row for each of the following parameters:

Minimum Melt Coefficient: The degree-day snow melt coefficient that occurs on December 21. Units are either in/hr-deg F or mm/hr-deg C.

Maximum Melt Coefficient: The degree-day snow melt coefficient that occurs on June 21. Units are either in/hr-deg F or mm/hr-deg C. For a short term simulation of less than a week or so it is acceptable to use a single value for both the minimum and maximum melt coefficients.

The minimum and maximum snow melt coefficients are used to estimate a melt coefficient that varies by day of the year. The latter is used in the following degree-day equation to compute the melt rate for any particular day: Melt Rate = (Melt Coefficient) * (Air Temperature - Base Temperature).

Base Temperature: Temperature at which snow begins to melt (degrees F or C).

Fraction Free Water Capacity: The volume of a snow pack's pore space which must fill with melted snow before liquid runoff from the pack begins, expressed as a fraction of snow pack depth.

Initial Snow Depth: Depth of snow at the start of the simulation (water equivalent depth in inches or millimeters).

Initial Free Water: Depth of melted water held within the pack at the start of the simulation (inches or mm). This number should be at or below the product of the initial snow depth and the fraction free water capacity.

Depth at 100% Cover: The depth of snow beyond which the entire area remains completely covered and is not subject to any areal depletion effect (inches or mm).

Plowable Impervious Area: The fraction of impervious area that is plowable and therefore is not subject to areal depletion.