Cold weather causes a spike in citrus prices, but it will drop back to normal shortly. Also, juice prices do not usually go up because a little frost does not hurt the insides of the fruit, just leaves marks on the outside so fruit that is sold is effected but not fruit that gets squeezed. 

Cold weather can affect citrus prices because 1) there is more labor involved in trying to save the crop and 2) if any crop is lost, the supply is lessened while the demand isn't. Either way the price goes up. Cold weather doesn't just affect citrus fruits, it can affect the prices of all crops. 

'"Normally, you could buy a box of tomatoes -- beautiful tomatoes -- for $8," said Campbell. "This time of the year, right now with this cold weather, we're spending anywhere from $18 to $30 a box."'