snow drifting around horizontal pipe on roof

huangyhg

snow drifting around horizontal pipe on roof
i am currently analyzing the feasibility of installing a 40" diameter pipe horizontally, along an existing monosloped roof that is 160 feet long.  this pipe is to be installed about 130 down from the high point of this roof that is sloped 1:12 (the roof at this point is about 10.83' lower (in elevation) than the high point.  once this pipe is installed, it should project about 4.5' from the roof level (to the top of pipe).  my questions are as follows:
1) i know that i have to consider windward drifting, but should i also consider leeward drifting at the same time?  the flat snow loading is about 1.5' high and the windward drifting is just over 3' high.  could drifting on this monosloped roof cause the windward pocket to fill in and cause additional leeward drifting on the other side.  should account for the leeward drifting the same time as the windward drifting?
2) if i can convince the client to reposition the pipe only 80 feet away from the high point (center of the roof), the top of snow drift should be about 6" below the top of pipe.  would it be feasible to neglect any possible leeward drifting in this case?
3) if i want to avoid snow drifting around this pipe all together, how high would i need to set the pipe?  i would guess that i would need to set the bottom of pipe about 6" higher than any possible snow drifting height.  (in other words, about 5' high to the underside of this pipe.)
thanks in advance for all your input!
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i would likely consider 15 psf per ft of height extending approximately 8' to 10' on either side of the pipe, without more correct information.
dik