St Louis here - very hot July and the irrigation people suggested I start a second watering cycle about 4 PM when the temperature is over 90 degrees.

I learned of IFTTT and attempted to do that. There is an applet for that. HOWEVER, you cannot set the day of the week and tell it not to run if there is rain. So if my system completed watering at 10 am and the temp goes over 90 degrees at 11 am, it will water at 11 am, not 4pm. If it rain next, and the applet says not to water, then the temperature goes over 90 degrees, you water in the rain.. 

Until IFTTT can allow multiple conditions, like day of week, time of day, rain, and temp, IFTTT is not a solution. The information is in the HD-12, it just needs the interface to accomplish this.