Answering what is a warm front depends on knowing cold fronts. Under normal circumstances warm air cannot displace a mass of cold air. Masses of cold air are often called cold fronts and are often denser than warm air. Since the two types of air have different densities and temperatures, they also cannot mix. What usually happens when there is a cold front is that warm air is displaced and moves over the cold air. This is because warm air is lighter. Once there, warm air will grow cooler and form into clouds.
In some cases, cold fronts will not cause any significant weather changes. If there is sufficient moisture however, cold fronts can lead to rain showers and thunderstorms that can last for weeks. Severe storms can even be accompanied by floods and tornadoes. Floods in particular do not quickly dissipate because cold fronts take some time to pass through.
So what is a warm front? They are simply what cold fronts are not. Warm fronts are the front portions of warm masses of air that move in to replace preceding cool air. As expected, air in front of the warm air mass is cooler than air behind warm fronts. In weather maps, it is represented by solid lines with semi circles or rounded lumps attached to the front of the lines. This is opposed to solid lines with pointed triangles that represent cold fronts.
Unlike cold fronts, warm fronts are not typically associated with devastation. This and other warm air mass conditions put warm fronts in stark contrast to cold fronts. The following are what you would expect when a warm air mass approaches or passes:
o Temperature conditions during warm fronts are opposite of that during cold fronts. Before a warm front passes, the temperature is noticeably cooler. If you are directly in line as a warm air mass passes, you will notice a quick change in temperature towards warmer levels.
o Cold fronts may lead to strong showers. Warm fronts however are typically accompanied only by light showers and drizzling especially as the warm front passes. Despite the drizzle though, surroundings can still feel more humid.
o Winds in the southern hemisphere will blow north to northeast. Those in the northern hemisphere will blow south to southeast. As the warm air mass passes, the direction of the winds will shift.
o Visibility as a warm front passes will be poor and hazy. Sometimes, fog can also form near the ground.
o Atmospheric pressure during the passage of warm fronts will fall and then rise and then fall again after it passes.