Here in NS we do classes from April ’til early Dec. Water 35F to about 55F and back to 40F (studentsand I) dive wet. Air goes cool, nice, cold. Then the warm water is a breeze when you use the shorty or less. To my way of thinking the only real difference is gearing up & off with all that heavy crap up here. Many do argue that warm water trained divers are stymied when diving cold water. They may be making mountains out of mole hills. But fresh water to salt with all it’s currents, tides, etc. is another story.