Want to know if it'll rain tomorrow? You no longer have to leave Facebook to find out. Facebook started offering weather "greetings" to some users in April last year, but now it's rolling out a fully fledged weather app on both desktop and mobile. The app is still not available to everyone. For example, I can access it on Android — it's located in the hamburger More menu (upper right corner) in the app, and listed under "Apps." On desktop, however, it's nowhere to be found.