I have a bran-new picnic table. It is made out of fur. So far I have one coat of an oil base exterior stain on it. In Wisconsin we have very extreme weather conditions; would it be okay or recommended to use a varnish or lacquer finish on the picnic table?
You would want to use a lacquer finish. It holds up better to the weather and puts a tighter seal on it. Not to mention it will look absolutely wonderful.
After the first coat of stain, do a light sanding and apply another coat of stain if you like. When you're happy with the color, apply a clear finish polyurethane and after a day or two, apply a second coat. You'll get a natural finish with no eventual peeling, flaking, etc. You might also consider covering the table with a waterproof tarp to cut down on the wear and tear to the table in the winter and spring.