I'm using one of these for our 1266 cfm blower.

Here is a link that might be useful: Fantech Caps

My parents have had one for decades, but not in a snowy environment. Grease is not a problem. With snow it would depend on how often you ran it since the warm air would melt the snow around it.

Many like the low profile style because it is low profile. If snow or grease are issues, then an upblast style housing (without the fan and motor) can be used, although available sizes might need to be adapted to a mere 8-inch duct. The flange extension it sits on can be fabricated to meet various roof pitches and anticipated snow depths.

The cover of the linked document illustrates what an upblast housing looks like.

kas

Here is a link that might be useful: example images of upblast housings

Thanks for the guidance everyone.