Actually, it's not even that involved. For the ultimate in weather simplicity, check out Umbrella Today? to know what to bring as you leave the house. You can set it up to text you on days that you'll need an umbrella too.
I'm finding more and more that people are creating apps or services just because they can but not necessarily because they solve any sort of problem. I love this example because it takes something we think about - weather - and breaks it down one step further, how will the weather affect me once I leave the house?
May I never be caught in a downpour again.
