While you may have a favorite weather app to turn to for what is happening near you, a lot of folks rely on whatever app is handy. For some that means the weather notifications through Google Now are perfect, while others rely on that quick glance baked into their favorite clock widget. Like most Android phones, the Galaxy S6 and S6 edge offers a clock widget with weather built in that pops up as soon as you hit the home screen for the first time. This same weather information is available on the lock screen, as well as the Information Stream on the Galaxy S6 edge. It's powered by Accuweather, and works reasonably well for offering up a quick glance at your current weather.
The only thing missing is the actual app. At least, that's how you'd probably feel if you went looking for this app in your launcher. What you're seeing here is another example of Samsung's integrated apps, which means you've got a couple of options for accessing and using the app to get your weather.
Samsung's Weather app essentially only exists within these widgets. You can tap on them to launch the full screen experience, which offers a more detailed look at your week and lets you see a larger map for comparing or selecting multiple cities to pull information from, but that's it. There are no other ways to access this information, which is both a good thing and a bad thing. If you don't want to use Accuweather at all, you can toggle the off switch on the lock screen and edge display and be done with it. There's no way to inject an alternative into these spaces, of course, but you won't have conflicting weather reports from two different services on your phone if you decided to install something you prefer to use.
It's a little unusual when compared to how you usually see Weather apps, but Samsung's integration makes a lot of sense here. The widget is how most folks use weather apps anyway, so it's one less icon in the drawer. The only downside would be folks who want to use a different clock widget, but since Accuweather is frequently an option on a lot of alternative clock and weather widgets it's a simple thing to navigate around.