Final answer:
The free air temperature is likely to decrease when climbing through a frontal surface during a flight in cold air behind a cold front.
Step-by-step explanation:
When a cold front passes through an area and you take off in cold air behind the front and climb through the frontal surface, the temperature of the free air is likely to decrease even further. This is because cold fronts usually bring in cooler air masses, and as you climb higher, you are moving into colder regions of the atmosphere. So, the free air temperature is likely to decrease as you climb through the frontal surface.