A boundary between two air masses of different density, moisture, or temperature is called a FRONT. Cloudiness , precipitation , and storms sometimes occur at frontal boundaries. Four types of fronts include cold, warm, occluded, and stationary.
A occluded Fronts involves 3 air masses of different temperature cold air , cool air, and warm air. A Occluded fronts may form when a cold air mass moves toward cool air with warm air between the two. A cold front can even take over a warm fronts
Stationary fronts occur when neither warm nor cold air advances. The two air masses reach a stalemate. That is what stationary means - that neither front is moving. These type of conditions can last for days, producing nothing but Altocumulus clouds. Temperatures remain stagnant and winds are gentle to nil.