I've been using this app on my smartphone a few years now, and its free on 1mobilemarket. Its called Radar Now! It has pay features if you want them but I just use the free version, Excellent when taking those long rides.
Hands down best radar app I've ever used on my iPhone is MyRadar. It automatically centers the map according to your current location and provides immediate radar animation from the moment the app is opened. Map can also be easily panned, pinched and zoomed. Has lots of overlay options, most of which I don't use. MyRadar and TWC Max are my two go-to weather apps for riding (and anytime).
It is even worth the upgrade to ditch the ads and stuff. I have used this for awhile now and wouldn't leave home without it! Saved my butt a few times on long trips.
Glad that others like and use it. I just love the simplicity of it. Open it up and bam - animated weather radar, right where you are! I'd actually love to have a constant display of that on my bike while I'm riding, right next to the GPS!