Why does the atmospheric pressure drop in thunderstorm weather? Why is the air pressure greater in winter than in summer?

It is generally believed that the relative molecular weight of water is relatively small (the relative molecular weight of water is 18 and that of air is 29), so the density of gas is relatively small. If the proportion of water vapor is relatively high, the air pressure will be relatively low. The formula of air pressure, fluid pressure = density * gravity acceleration * height, low air pressure will lead to an increase in relative humidity. A high proportion of water vapor will lead to a low pressure before rain.

The second problem, because the heat expands and contracts, the gas density is high in winter, and the pressure will be high!