SebastianK

This Plugin is very easy to handle. Just install with a few clicks and set it up in your configs. 
Then include it in your sidebar e.g. with the following code:
< ?php spWeatherShow(); ? > (without spaces)

spWeather

This Plugin gets the weather from google.de/google.com and shows the weather now and a 4 days forecast with tiny pics

maennchen1.de

This plugin easily displays a weather widget with a destination of your choice. No PHP or Shortcode, just a widget. 
It caches the requests to the weather database in given intervals. 
You will need a free account at https://home.openweathermap.org/users/sign_up .
Font-Icons by Erik Flowers: https://erikflowers.github.io/weather-icons/

m1.MiniWeather

love the design

This plugin easily displays a weather widget (icon + temperature) with a destination of your choice.

spWeather vs m1.MiniWeather