This air carries high a volume of humidity with the air, and as it comes into the attic, if the temp is below 32° it freezes onto the underside of the roof sheathing and the trusses.
During the spring thaw, it compacts the insulation, sags the sheetrock ceiling, and stains the ceiling.
When the humidity level is high it enters the edges of the roof sheathing, swelling the edges giving the look of big rectangles on the roof. If the back side of the shingles get wet then the shingles curl.
The exterior of the house must have air, trees overhanging the house stop air movement and keeping the humidity level very high.
This will cause the roof to fail 5-15 years earlier than it should.