My partner has an uncanny ability to under-dress for the weather, so I've taken a personal interest in Cloth, a fashion-social app with an interesting integrated weather feature which offers appropriate outfits according to the weather so you don't step out without a sweater, coat, or scarf...
At the heart of Cloth is a fashion/outfit documenting app with a one-touch social-network sharing feature to push photos of your best ensembles to Facebook, Twitter, and Tumblr. There are even some Instagram-ish filters to stylize your photos for your archives. But Cloth recently added another feature which elevates the app's utility: connecting archived and tagged outfits with realtime weather forecasts.
So for example,Cloth will tag an outfit with the designations of Hot, Warm, Chilly, Freezing, Rain or Snow by the days you've worn the outfit, thus customizing your clothing-to-weather preferences (because for one person 72 degrees is warm, while for another it may be time to put on a scarf). The app then can match weather forecasts in "glanceable information" format after this initial tagging sequence, offering users a quick archive of outfits to match the day's temperature/weather.
For someone like myself who just "throws together something" except for special occasions (and who has a better track record of dressing appropriately for the weather), I can't see myself documenting my outfits using Cloth. But more fashionable iPhone-toting users with a habit of forgetting to bring a sweater have nothing to lose since the Cloth app is currently free over at iTunes.