• Constant - applies the same load magnitude to the entire load polygon
• Drift - Snow drift loads are represented by a surface load polygon with a sloping plane (i.e., a varying magnitude). In order to define the magnitude and slope of the drift plane it is necessary to define the magnitudes of the snow load at any three vertices of the snow load polygon. For each Snow drift property created in PropTable – Loads – Snow, three Magnitudes are specified. Then when Snow Load polygons are laid out using the Layout – Loads – Snow Loads – Add command (see Section 3.16), each of the three magnitudes will be assigned to and associated with a vertex of the Snow Load polygon.
  Note: For a given Snow Load property all three Magnitudes can be given the same value (which would be the same as specifying a Constant snow load of that magnitude), or for complex drift patterns they can be given three different values, but for the most common drift conditions two of the magnitudes will be the same. When the magnitudes at three points are known, the program can calculate the magnitude at any other point within the polygon.

Constant snow loads and Drift snow loads are not additive, even if the Drift snow load polygon is laid over a Constant snow load polygon; whichever polygon is on top is the one that will be used to calculate the member loads. Thus the Magnitudes specified must be the total magnitude at that point, not just the additional load of the drifting snow above the constant snow load.

Since a drift snow load property is defined by a plane, complicated snow drift patterns may need to be modeled as separate snow load polygons.