No weather forecast is more annoying than a 30% chance of rain all day. It basically means nothing.
Optimists could get caught in the rain while others could plan a whole day indoors (particularly if you’ve got a little one) only to realize after the fact that you could have gone outside after all.
Dark Sky, which I heard about on NY1, puts an end to the doubt.
It does one thing and one thing only: accurately let you know if it will be raining where you are in the next hour.
It’s been quite useful to me and is well worth the few dollars.