This one is pretty easy. From the main menu, choose "Events" then "Competitive" and choose "Community Events". You will have a choice of different events like the daily, weekly or monthly. Find an event that looks like its sunny and select it. Once in the event details you will see the stage that will show the name, length, etc. On the bottom right of it box will be a weather icon that denotes what kind of weather the stage will have. If it has a sun, it will be considered sunny conditions. Just because the pic of the event looks sunny doesn't always mean its gonna be sunny so always look for that weather icon in the event details. Just finish the stage and the trophy will pop