by David Murphy
A warm front represents the leading edge of warm air moving into a region of cooler air. It's shown on a weather map as a red line with half-circle pips pointing in the direction the front is moving. As in the case of cold fronts, warm fronts form as part of low pressure centers and actually represent the movement of warm air around the center of the host low. That's why warm fronts are usually pictured on weather maps with one end protruding from a low.
Warm fronts usually preceed cold fronts into a given region, sometimes by a day or more. In fact, they are almost always part of the same weather system that produces a future cold front. Warm fronts move from the west at first, but then usually swing into more of a northerly movement before dying away. Picture the front acting like a backwards-moving clock hand, rotating from 6 o'clock to 3 and then perhaps to 2 or even 1 before fading.
The air behind warm fronts is not only warmer than the air ahead of it, it's usually wetter.