How does applewatch add colorful clouds to the dial?

Check the current temperature and weather of the day: open the "Weather" App on Apple Watch. Tap a city, and then tap the display to cycle through the hourly rain forecast, weather conditions or temperature.

Check the air quality, ultraviolet index and wind speed information, and the weather forecast in 10 days: click on the city, and then scroll down. Not all areas have air quality readings in the upper left corner.