A warm front forms when a warm air mass pushes into a cooler air mass with the warm air rising over the denser cold air. Winds preceding a warm front are often from the SE. The barometer falls slowly. Warm fronts are less distinct than cold fronts.
High clouds like cirrus, cirrostratus, and middle clouds like altostratus are often ahead of a warm front. These clouds form in the warm air that is high above the cool air.
As the front passes over an area, the clouds become lower, and rain or showers are likely. Areas of fog can form, especially with slow moving fronts. There can be thunderstorms around the warm front if the air is unstable.