In the last release of Weather Watcher, the Weather Watcher windows would always load on the first monitor... no matter which montor they were last viewed on. The current Weather Watcher release will resolve that issue.
I am working on rebuilding the entire map feature to include multiple monitor support. I don't want to go into too much detail at this point, but I can tell you that you'll be able to drop numerous maps on multiple monitors. It'll be very cool