>If you look at wwh's chart, Faldage, and locate eleven, you'll see the place where the two factors required for snow in Richmond, VA, intercepted at 11.

if you'll pardon the intrusion, I think the "11" is confusing matters in use of the charts. there are no 11's on the F chart, and I rather suspect Loftan was talking about degrees F. (I doubt that it snows at 11 degrees C, even in brumal North Dakota.)