Ray, I had my new OS up and running yesterday for the first time and selected the Zimmerman method. I noticed that it said 38% the whole day and that it only predicted it would be cloudy. It started to rain later in the day and then heavily in the night. As you mentioned above, it clearly kept to the 38% from the previous day’s data and then watered overnight. Something I did not want due to the fact that it rained.
Today I installed a rain sensor, so I expect that moving forward, if it rains, regardless of what would have been the percentage of watering, the rain sensor will override that and not water.
I wonder if in a future update the % calculated by either the ET or Zimmerman method might be able to dynamically update throughout the day based on changed weather conditions. i.e. if there was no rain predicted in the morning, but an unexpected storm blew in, it could note that from the updated weather information and then adjust the % as required?