@mcmuller: Bad news! Thanks for the notice.
WUnderground officials describe some exceptions for Personal Weather Station owners or developers who use WU API data for non-commercial purposes. I am not sure if this works out for OpenSprinkler owners who like to use the Zimmerman method to control the garden watering. There might be as well some software/firmware adaptations needed for OpenSprinkler to stick with the new WUnderground service, if possible at all?
I hope that we can get some information from Ray or Samer which weather service they like to use in the future? The current OWM interface implementation isn’t really as good as the WUnderground interface for OpenSprinkler.