Before you go recomending the placement of an elbow on the top of the vent make sure the manufacture of the furnace allows that as not all manufactures advise or approve this. The water and snow that may fall down the pipe but the amount that does go down woll be taken care of by the furnace condensate removal system. Jerry does have a good point on the distance between both vents may not be proper.

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Well thats my 2 cents.
Brian Kelly
Kelly Home Inspections