There are lot of apps in play store that help you in displaying Weather in Calendar in Samsung Galaxy S7 , you can also do this all you need is to follow below steps
Install S Planner app from Play store this app is helpful as it help you in deciding how you plan your holiday and trip.You can also check below video how he done that without the help of any app. this is done in samsung s5 and you can do also in samsung s7 just follow same steps in samsung s7
Add the Weather and Clock widget Samsung Galaxy S7
1. To add a widgets, touch and hold an empty area on the screen. Then touch Widgets.
Note : You can also pinch your fingers together on the screen to acces the menu.
2. Swipe to the right (or to the left) to access all available widgets until you find the Weather widgets.
3. Touch the Weather widgets to access all the widgets this category hold.
4. Touch and hold the Weather and Clock widget, then drag it to a Home screen and release it.
Note : You can adjust the size of the widget by dragging the sides of the blue frame.
5. Once the widget is set, touch the icon representing a cloud to add the weather predictions corresponding to your city.