Of all of the environmental effects, wind has probably the largest impact on blower door testing.  If you have to test under windy conditions, try to set up the Blower Door on the leeward (downwind) side of the house. Also place your outside reference tube toward the center of the leeward side of the house close to the house.  If it looks like it might rain, tape the tube to the house with the opening pointing down and close to the ground.