balanced snow load heigh

huangyhg

balanced snow load height
in figure 7-8 of asce7-05, how do you determine h-sub-b, the height of the balanced snow load?  most localities just provide the ground snow load in terms of pounds per square foot, not a depth of snow fall.  is there a standard unit weight for snow that you are supposed to use, or is there some other way to determine h-sub-b?
see eqn. 7-3.