On Wed, 28 Oct 2020 08:44:21 -0000, Brian Gaff \(Sofa\) wrote:

I am going back a way here, but I distinctly recall the up and down
vents in a generator cover to stop the water getting in while air still
did.

Louver. Though wind driven rain will get past a single louver and
powder snow won't even notice it's there. B-)

Back to back louvers with a gap in the middle between the slats would
probably keep most rain out, not so sure about powder snow.

--
Cheers
Dave.