@binaryos, not quite sure how you generated the numbers so I may be misunderstanding your table…
But the drop off of watering level in the evening seen from the OS Weather Service when using OWM is interesting. OWM does not provide historic information so the logic used in the OS Weather Service is to use tomorrow’s forecast temps. This means that watering level may change during the day as new forecasts are provided. Also, there is no guarantee that the temperatures are what your PWS provided as the OWM call uses lat/long rather than a specific PWS id so you may be getting an average for, say, the city rather than your backyard.
This is very different to the logic that was used for WU. In that scenario the OS Weather Service used yesterday’s temperature and humidity which by definition would be a constant during the current day. So the WU logic provided a relatively stable watering level through out the course of the day. Only rainfall would result in a “within day” change in the watering level. In this scenario, if you have specified a PWS ID then the data used in the calculation is the data provided by the specific PWS and not some local average.
So the logic is very different, the OWM approach sets watering level based on how hot it is going to be in the general area whereas the WU approach sets watering level based on how hot it was yesterday at your PWS. For me, the WU approach was more intuitive and far less volatile than the current OWM approach but debateable as to which is preferred by the plants !