Answer to Question 1
Answer: Warm fronts separate advancing masses of warm air from the colder air ahead. As with cold fronts, the differing densities of the two air masses discourage mixing, so the warm air flows upward along the boundary. This process is called overrunning. Warm fronts are about half as steep as cold fronts (their slopes are about 1:200), which causes the lifting of the warm air to extend for greater horizontal distances than for cold fronts.
Answer to Question 2
Answer: First, high clouds (cirrus, cirrostratus, cirrocumulus) appear. As the warm front approaches, the clouds thicken and lower into middle clouds (altostratus). Finally, near the warm front, stratus and nimbostratus are seen. As the warm front passes, the clouds usually decrease.