With a "Premium" upgrade, the widget can access more detailed data ("feels like" temperature, UV index, forecasted precipitation likelihood etc.) powered by the Dark Sky weather data service (it's a paid service, which is why the Premium option costs a bit more).
It provides a highly customizable, very compact, beautifully designed widget in the "Today" view on your iPhone, iPod Touch or iPad, which displays the current weather (and, optionally, a forecast) for your location.
To add the widget to your Today view, once you've installed the app, just swipe down from the top of the screen, select the "Today" tab, and then find the "Edit" button at the bottom of the page.
The free version features high quality weather data for your area from OpenWeatherMap.
Simple Weather Widget is simply the best weather widget in the App Store.