I just noticed that in OpenSprinkler the average temperature used (see Weather Diagnostic pop-up example) is not aligned with the one provided by Weather Underground itself (see WU screenshot).
Basically I think that OSpi calculates Mean Temperature as (High + Low) / 2 instead of using the Actual Daily Avg.
In a day like yesterday (June 2nd), with high difference High/Low but real temp decrease only over night, this can bring to a significant difference => signifcant water level difference:
June 2nd – WU
High => 29.7 °C
Low => 17.7 °C
Avg => 24.6 °C
June 2nd – OSpi
Mean Temp => 23.7 °C
Can you check it out if my theory is right ?