I'm making a YouTube video about a tornado in a campfire I videorecorded. I want to show my viewers the mechanics of the tornado.
Here's a screen shot of what I'm after:

I'm not looking to be a Blender expert (although it looks like a neat program to learn.) I just want to render a 2 turn spiral that I can rotate.
I tried making a spiral from the add curves. I made it taper as it got higher. I extruded the curve in the Z direction and hacked my way thru disconnecting a segment and connecting two, to complete a mesh. It's exactly what I want, but Blender doesn't see it as a solid. (No faces.)
When I made a "flat" spiral (that is, no taper in Z), I can extrude it in Properties and Blender sees that as a solid. But I can't figure out how to taper it in Z after the fact.