Understanding the dynamics of weather fronts is one of the most critical things you need to know as a pilot. A high percentages of accidents are caused by encounters with poor weather, but with a good understanding of frontal systems, your weather briefing and flight planning can be a whole lot more effective.

Cold Fronts

Cold fronts are cold, dense air masses that encounter warm, light air masses, pushing the warm air up into the atmosphere. You can think of a cold front as a snowplow on a truck, pushing the snow, or in this case warm air, up and out of the way.

Along the steep edge of a cold front, you'll often find cumulus and cumulonimbus clouds, because of the rapidly rising warm air. This is why cold fronts are associated with squall lines, thunderstorms, frontal turbulence, and overall bad weather like what's pictured below.

Warm Fronts

When a faster-moving warm front encounters a slower cold front, the warm air pushes up and over the colder air, because it's less dense. Lifting action with warm fronts is much more gradual than what's found with cold fronts. But there's also some bad weather associated with warm fronts.

Rain or other precipitation from a warm front falls into the colder air below, causing widespread precipitation, fog, low ceilings/visibilities, and heavy snow (during colder months of the year). And if the warm front moves slowly across the ground, you'll often find several days of poor weather and IFR conditions.

Stationary Fronts

They're shown on a surface analysis chart with alternating cold and warm front symbols, because the frontal boundary of a stationary front can be thought of as a tug of war game between the cold and warm air masses, with characteristics from both.

Weather found along the front usually reflects the more dominant air mass. And while thunderstorms are possible, you're more likely to find stratus clouds and steady, light rain or drizzle. Stationary fronts tend to cover large areas in IMC, with calm surface winds that parallel the frontal boundary.

Occluded Fronts

Let's just say occluded fronts aren't great for flying... They happen when cold fronts catch up and overtake warm fronts ahead of them. The end result is two fronts in one area, one at the surface, and one aloft/above the other. Since this type of front is so unstable, you often see widespread cloudiness, precipitation, and thunderstorms (some of which may be embedded, or hidden within clouds).

There are two types of occluded fronts: 1) In a cold front occlusion, cold air pushes underneath a warm air mass, forcing it skyward. Just like in the diagram above. 2) On the contrary, in a warm front occlusion, warmer air overruns colder air. But in both cases, warmer air is lifted between the two air masses.

Fronts can be complex, but with a good understand of the weather that's associated with each of them, you'll have a lot easier time planning your next flight, and understanding what your weather briefer is telling you.