Hmm, this involves a number of steps and I don’t know if the stock firmware can do this. The only feature that relates to ‘open a valve then each zone for 30 seconds’ would be to set it as program 1, and set it to disabled, so it won’t normally run. But then have the sensor hooked up to OpenSprinkler and set the sensor type to Program Switch. So when the sensor is activate, it triggers program 1 to run.
Another option is to perhaps use IFTTT — when temp goes below blah, trigger OpenSprinkler to perform certain actions. But there the temp is from some weather channel, not the temp at your house etc. (unless if you have a smart temperature sensor that can send data to IFTTT).