I get asked from time to time what weather apps I use on my smartphone. Let me say at the outset that I am a minimal smartphone user, so I am probably not the person to ask about this. But I do have a couple of apps on my phone so I can check the radar and get a quick forecast. I also want to have at least one app that can give me a warning if my area is under a severe weather warning of some sort. I was interested to read this CoCoRaHS blog post about how to add a National Weather Service page to my smartphone home screen, because I love the NWS (I am a former employee) and prefer to use their forecasts over most commercial sites. You can read the blog post here. I found the instructions very easy to follow.
If you are wondering why the NWS does not have an app, this Forbes post from Dr. Marshall Shepherd of UGA may shed some light on it.