One of the things that makes pressure change is temperature. Luckily, pressure changes so we get to enjoy both sunny and cloudy days. The best way to think of an occluded front is to visualize a cold front and a warm front coming together and one riding over the other. In each case, the colder air will remain at the surface, lifting the warmer air. That's why on a weather map we show an occluded front with the symbol of both the warm and cold front.
Water vapor is an invisible form of water in the air.
Warm air can hold more water as vapor than cold air. When the air temperature falls to the dew point temperature, dew will start to form on surfaces or fog can form in the air. Dew point temperature is, in effect, a measure of the amount of moisture in the air. If the dew point temperature is much lower that the air temperature, the air is dry. Temperature never falls below the dew point temperatures.