This is on Windows 7 SP1 x64 Professional with multiple monitors using DisplayFusion V3.5.0. DisplayFusion implements taskbars on the non-primary monitors and these taskbars have a Notification Tray that mimics the Windows taskbar Notification Tray on the primary monitor.

When hovering over the WWL temperature icon in Notification Tray of the non-primary monitor, the WWL tooltip displays on the primary monitor instead of on the non-primary monitor. The DisplayFusion developers have investigated this and find that they are not able to control which monitor the WWL tooltip opens on. This needs to be done within WWL.

Can you effect this change in WWL to make the tooltip open on the proper non-primary monitor?

The problem is that the Weather Watcher Live tooltip window is not a standard tooltip window, so it's position is not controlled by Windows. The best you could do is click the "Use custom tray tooltip window location" in the "Tray Icon" --> "Tooltip" section of the Weather Watcher Live Options window and manually set the location of the tooltip window. And, then always hover over the tray icon closest to that location.

This is an acceptable "solution" for dual monitors side by side. However, I feel it might be less acceptable for 3+ monitors, or even dual monitors one on top of the other . JMO
It's a subtle matter of the eyes tracking the mouse position.

Thanks for your response.

You could turn off the skinned tooltip window by unchecking the "Use skinned tray tooltip window" in the "Tray Icon" --> "Tooltip" section of the Weather Watcher Live Options window. Weather Watcher Live will then display the standard tooltip (like your other system tray icons are doing) and Windows will be able to properly control it's position. Again, that might not be an ideal solution either, but it'll work best for your setup.

Yeah! That does work correctly. Can you make it display all the selected items in the Tooltip or is there a size limitation when the Tooltip is set like this?

Windows has a size limitation for the standard tooltip. When you hit that limit, the remaining text will be cut off. That's why I created the skinned tooltip window. And, unfortunately, that has other limitations.