umbee is fully open source. More information is available here: https://github.com/derekbrameyer/umbee

Do you ever forget to take an umbrella with you in the morning? Fix that with umbee! You'll receive a silent notification at your chosen time that indicates the precipitation chance for the morning and for the afternoon, as well as whether umbee thinks you need your umbrella that day. When you wake up in the morning and check your phone, umbee will already have figured out whether you'll need that umbrella, eliminating that "D'oh!" moment when it starts raining halfway to work.

Using the advanced options, you can customize threshold values and change your alert type. You can also set umbee up to notify you with tomorrow's precipitation data, so you can have an evening notification to prepare you for the next day.

Feedback is more than welcome!