Google has begun rolling out a feature Google Home visualization feature today, allowing you to ask Google Assistant to display the weather forecast on your Chromecast enabled device. The new feature is a cloud-side change so there is nothing for you to do. You will know when you have the feature on your account when you ask Assistant on your Google Home, “Hey Google, show me the weather on my Chromecast”.
Visualizations with Assistant and Home were shows last year at Google I/O as a way to improve getting personalized content. In the case of the weather, you can visually see the weather forecast instead of having to listen to Assistant read it back to you on your device or Google Home.
At I/O, examples of being able to see your calendar appointments and being able to see Google Maps information and have it sync to your phone as you leave were shows as possible uses. Weather, admittedly, is low hanging fruit but it gives you an idea of what Google has in mind with the feature.
Right now, the feature appears to only be working for US-based Google Home users but that could be changing rapidly as Google distributes the feature (assuming local laws allow it). Also, the feature only works with Google Home or devices with Assistant built into them. It will not work with phones, at least right now.