Precipitation anomaly is very important for agriculture and gardening.
But plants and crops are used to what they habitually get, not a fixed amount.
Adding a relative % change compared to normal precipitation would be very interesting as a map overlay.
The current absolute anomaly tends to make wetter regions look a lot worse overall than drier ones even when those drier ones are also getting high relative % changes. 
Just a suggestion!
Keep up the good work, your site is great!
