While your apps like News and Stocks have moved from iOS to the Mac, there is no default Weather app for the Mac. But you can get weather information quickly and easily using Spotlight, Safari, the Dashboard, Notifications Center and Siri. You can also bookmark or create a shortcut to your favorite weather source or get a third-party app.
I really wish Apple would just give us the same weather and calculator app that iOS has on the iPhone for the Mac and the iPad.
This is yet another example of Apples product fragmentation.
AMEN. This i why I haven't upgraded to Mojave.