After upgrading to firmware v2.1.0, the log entries appeared in the UI. The following entries appeared:
7/18/2016, 4:26:22 PM] : Sensor open - Rain sensor - tripped
[7/19/2016, 4:30:00 AM] : Water cancels - AM Schedule, AM Watering not run: System delayed
[7/19/2016, 2:23:09 PM] : Sensor close - Rain sensor
Not sure why these did not appear in previous firmware versions.