If you're looking for the best iPhone weather app, look no further than The Weather Channel. This app is far easier to use, and from what I've seen more accurate than my previous favorite Weatherbug.
The Weather Channel provides an hourly forecast, a 36 hour forecast, as well as the traditional 10 day forecast.
Choosing a new location is a click away, and you don't have to add the new locations as favorites just to see the weather.
My favorite feature however is the weather map. You can choose to see precipitation, cloud cover, both, and many other overlays.
Having the weather in your hand is convenient if you're someone that travels frequently or just plays outside a lot. Having this app in your pocket is empowering.
Be prepared, download The Weather Channel now. It is free.