This is neat.  They took weather (the proverbial most complicated thing ever) and reduced it to a simple yes or no.  Not everything can be this simple, but this manages to answer a relevant question and stay really useful.  That might be a good axiom of reduction: stay useful.

Where Umbrella Today? really shines, though, is on the next page where you can sign up to be notified by SMS (at a time of your choosing) on the days where you do need an umbrella.  Now that’s more than useful, it’s handy (which I believe is about 150% more useful than just useful on its own).