HI ihstiv,
Thanks for your question.
When you select the "Deactivate on Precipitation" option, Lawncheck checks the current condition code weather code for your zip before sending the irrigation command. If the current condition code at that time does not indicate any type of precipitation, the irrigation command goes through. There are times around San Jose when it will rain from 5am to 6am and then abruptly stop raining, and the Yahoo weather condition code for the zip will change to "cloudy." If a command was scheduled to be delivered when the condition code was cloudy, it would miss the fact that it rained.
LawnCheck doesn't monitor condition codes for your zip code on a 24 hour basis. This might be an interesting upgrade, because then it might provide better irrigation information, but for now, only at the time the irrigation command is sent.
In the meantime, the best way to block during and after rain is a local rain sensor with rain brain turned on. The combination a local sensor with rain brain, and Yahoo weather is even better. My report log shows cycles stopped by Yahoo weather before it rains at my location because I use a zip code that is to the west of my actual location, and most rain comes in from the west in this area.
Hope this explains,
Jim