I have a snow board that is 3/4" plywood, painted white that I will place in different locations depending on the potential winds of a storm. Last night I had the board on my back porch. I cleared the board after 6.5 hrs (4.8")...I woke up this morning and checked it at 7:10, It was at 8.5" on one side and 7.8" on the other side. I would assume this is due to the wind, not knowing what the actual number was I averaged the number and went with 8.15" + 4.8" = 12.95" total. Finding lots of numbers around the property of 12 and 13, i decided to call it 13"....It does seem high compared to other numbers, but there are so many variables to take into consideration...