Here's a webcam showing the top of Pilatus. That will give you an idea of what to expect from the views today. Pretty much in the cloud as I write this.

The Rigi is looking a good bit better this morning.

What I would probably do, is to head over to Luzern. Many of the train stations have free wifi. Zürich and Luzern both do. When you arrive, have a look at the webcams for Pilatus and Rigi. Then decide if one of them is decent.

Plan B: When you get to Luzern, and the weather atop the Rigi and Pilatus is bad. I would then take the train across the Brünig, futher to Interlaken, and then up Wengen or Grindelwald (If you have time, otherwise just continue from Interlaken), then back to Zürich via Bern (or if you have time, back over the Brünig via Luzern to Zürich).

Since you have the pass, you can just hop on any train you wish. But check the schedules on the SBB site.