It is the weather. My wife's…
It is the weather. My wife's Accord hybrid below freezing the mileage drops. I believe the engine has to work more to create heat to heat the car. On a summer day sitting idle the engine will randomly turn on and the duration it is off is pretty long. In cold weather I have observed the engine kicking on after 10-15 seconds. Her precious hybrid Prius was similar, lower mileage in the cold.