If it is 0 degrees today, and it is going to be twice as cold tomorrow, how cold will it be?
Well, let's look at it this way. 0 (degrees C I will assume) is 273 degrees kelvin. If it was going to be TWICE as HOT tomorrow it would be 546 kelvin or 273 C With this in mind, I would say 'Twice as cold' is 1/2 the temperature or 137 K tomorrow or -137C
(which is -214 F) Unrealistic, for sure.