why is the air colder in the valleys in the winter time though hotter in the summer time?

Question

compared to not being in the valley

Answer 1

A fundamental axiom: cold air is heavier than warm air.

Thus, cold air sinks (like into a valley) and hot air rises.

However, the temperature gradient (how temperature changes with increasing altitude) is negative. This means air gets colder as altitude increases. So what we have is cold air at altitude pushing down on warm air near ground level.

The warm air heat comes from the ground, which is heated by our Sun. In summer, there is a lot more of that solar energy to heat the ground and lower air in the valley than in winter. Thus, the valley air is warm. In fact, the weight of the colder upper air contributes a little bit to the heat below because a gas under pressure does heat up. But in winter, when there is far less solar energy and resulting heat, the naturally colder air above settles into the valley.

Both the cold and warm air are more or less trapped in the valley because of the hills or mountains surrounding it. Thus, the cold air stays colder because no warm air is blown from the surroundings into the valley. And the warm air stays warmer because no cold air is blown into it.

Answer 2

Cold air gets trapped in a valley. if there is no way for the air to escape ie, wind, cold front and so on. It just stays there and gets colder and colder untill a cold front pushes it away or a windstorm. sometimes a cold front can push away the trapped cold air in a valley And the air actually warms up.

Answer 3

Because it traps whatever air there is in it hot or cold.