Mostly it's just that I live in Wyoming and the winds are hellacious and unpredictable. I do have some pictures though:Any building, even a house, with soffit vents, ridge vents, cable end vents etc, can find blowing, dry, powder snow filtering in. Some attics of houses have this issue and sometimes the homeowner isn't aware of it.
The wind can blow dry snow in directly and/or the snow powder can be "sucked" in through soffits or overhands in other areas. Typically, this is result of an overhang without enough length, roof without enough pitch or other architectural design flaws creating issues that the builder didn't see coming. Special care has to be taken in areas with dry blowing snow, to prevent this. Without seeing your barn, it is difficult to make recommendations. Fixing the issue might prove to be simple to extremely difficult. Sorry.
Looking at the barn opening from outside.
This is standing in the opening of the barn. As you can see there is a large open area on the right. You can barely see the door to the "coop" on the left. The wall on the left does not go all the way up to the ceiling which is my venting.
And this is standing in the back of the coop. You can see the door to the main barn and the light shining in from the barn opening. I have walked into this room in the past to find every single surface absolutely covered in snow. It is not getting in through anywhere but the barn opening. The crazy thing is that the barn opening is facing south and our wind NORMALLY blows from the east. It gets all crazy and circular a lot in the winter. If you live in the south just imagine a hurricane without the moisture. We get THAT type of wind. SO I have 22 chickens and 5 guineas that will be staying in here this winter. You can barely see on the far left corner of the coop picture 12 of my chickens hanging out on the ground so you can see how large the coop is. I don't believe their body heat will be able to keep it warm if it's getting coated in snow.
So, should I tarp the vents or no???