Dear John and WeatherCat network admins, . . .
It has been years since I've been really up on IP troubleshooting, but fortunately IP scanners are relatively easy to use. I have 2 devices that predate Bonjour, so I do need to hunt them down on our household LAN from time to time. Our fearless leader Stu (Stuart Ball, WeatherCat developer) recommended another free IP scanner - Angry IP Scanner:
http://angryip.org/Being a peace-loving person, I can't say I like the title, but it is perfectly usable software and you can just download it avoiding any Mac App Store hassles.
I assume there are a number of these utilities, so pick the one that suits your fancy.
Glad that you are on your way to getting your station up and running on WeatherCat! Should you have any other questions don't hesitate to ask!
Cheers, Edouard