Mathematically speaking its going to be -136.575 degrees tomorrow :-)
Since in absolute temperature i.e Kelvin. As 0 degrees would be 273.15 Kelvin. Half of it is 136.575 kelvin which is -136.575 degrees celcius.
However I guess it depends from person to person how they perceive the sense of temperature and the relationship of Temperature to their sensory organs perception of how cold it is. So the average person would feel that it is twice as cold as it was yesterday.