In this video lesson you will learn about how air masses with different characteristics create weather fronts. You will also identify the different types of fronts, as well as what type of weather occurs along them.
What Are Weather Fronts?
A long time ago, armies didn't have guns, grenades or fighter jets. They fought on the ground, face to face. An army ready to fight would consist of lines of men, each line with a specific job. In general, the front line was a strong line of shielded soldiers forging ahead, protecting those behind it.
Weather fronts act just like the front line of an army. Fronts are contact zones between two different air masses, and you can think of the air masses as the advancing armies, just with different pressure, density, temperature and moisture. And just like there's conflict between the battling armies, air masses 'battle' along fronts, creating changes in weather conditions. There are four types of fronts, and the type of front we get depends on which type of air mass, or army, is advancing over the other.
A cold front is the contact boundary of an advancing cold air mass over a stationary warm air mass. Conversely, a warm front is the contact boundary of an advancing warm air mass over a stationary cold air mass. This makes sense - the front is described by the type of air mass winning the 'fight.'
On a weather map, you'll see these symbols for a cold or warm front. The color helps you identify which type of front is moving in (blue for cold, red for warm), and the arrows tell you which direction the advancing air mass is coming from.
Warm and Cold Fronts
A stationary front is just what it sounds like: When neither air mass is advancing over the other. They are both stationary, and so is the front - the armies are at a stalemate. Finally, an occluded front is when a cold front overtakes a warm front. This happens because cold fronts move faster than warm fronts, so it's like one army is sneaking up from behind and taking over in a surprise attack.
On a weather map, you will see these symbols for a stationary or occluded front. As you can see with the stationary front, neither air mass is advancing. With an occluded front, the cold air mass is advancing over the warm air mass from behind.
Stationary and Occluded Weather Fronts
How Fronts Affect Weather
Just because they didn't have machine guns or grenades doesn't mean that battles weren't bloody. When two opposing armies fight, things can get very violent and dangerous because each side believes very strongly in what they're fighting for.
Weather fronts do the same thing - they advance forward, creating weather changes and sometimes even violent storms along the front. This is like the front line of battle on both sides - the initial point of battle contact.
Thunderstorms are common along cold fronts. This is because when a cold front occurs from a cold air mass moving into a warm air mass, the warm air is forced upward. When warm air rises, it cools, and since cool air can't hold as much moisture as warm air, the water in the air gets forced out, which is what creates clouds. Since the air is moving straight up, it forms a vertical cloud, which leads to thunderstorms along the front. However, behind the front, the skies are clear and the weather is calm.
Along warm fronts, storms are less intense and more drawn out. This is because the warm air moving in over the cold air rises gradually instead of quickly. Along the front, expect overcast skies and drizzle or light rain. Behind the front, the air will be warm and clouds will be pretty scattered.
Think about it like this: Thunderstorms generally develop quickly and are very dramatic storms. This comes from the quick, dramatic rise of the warm air when a cold air mass moves in. You know how it feels when you jump into a cold pool? It's a shocking feeling, and you're likely to jump right back out! When you step into a warm hot tub though, it's a little less dramatic, and your body reacts much more gradually. The same thing happens with a warm front, when the warm air slowly moves up over the cold air mass it's taking over.
Because stationary fronts are like stalemates, they can last for many days. Both armies are winning (or losing) equally in the battle, and neither is willing to give in. Eventually, the stalemate will end because one side will take over, creating a cold or warm front, or the front will simply dissipate because the two sides just don't feel like fighting any longer. Long days of rain and clouds accompany stationary fronts.
Because an occluded front is when a cold front overtakes a warm front, this can lead to some really rainy weather! The cold front comes in from behind and literally wedges itself under the warm front, lifting it up. This means that the zone of contact between the two fronts is up in the air, not on the ground.
This also pushes any warm air up that was between the two fronts, which as we now know creates rain and thunderstorms, depending on how quickly that warm air rises. Each front still retains its army though. The weather behind the occluded front is similar to that of a cold front, and the weather ahead of the occluded front is similar to that of a warm front.
Like two armies at battle, air masses also battle with weather. When two air masses meet, we get weather fronts, and the type of front depends on the type of air mass advancing. The differences in the air masses come from differences in air pressure, temperature, moisture and density.
A cold front is when a cold air mass moves into the area of a stationary warm air mass. Like jumping into a cold pool, a cold front 'shocks' the warm air upward very quickly. This sharp rising of warm air creates thunderstorms along the front, while behind the front, skies are clear.
A warm front is when a warm air mass moves into the area of a stationary cold air mass. You wouldn't dive into a hot tub, would you? You're more likely to slowly step in and let your body adjust. Warm fronts are the same way - the warm air rises slowly and gradually over the cold air mass, creating gray skies and drizzle.
A stationary front is a stalemate. This is when neither air mass is advancing over the other, and you can expect rain and clouds to accompany this type of front. Like two armies in battle that are equally winning or losing, these fronts can last for long periods of time.
When a cold front overtakes a warm front, we get an occluded front. This is like one army sneaking up and attacking the other army from behind. The fronts do not overlap; the cold front literally pushes the warm front up off the ground. When these two fronts come together, we get a wide area of rainy weather along the front, but weather similar to cold fronts behind and similar to warm fronts ahead.
As you finish this lesson, you should be able to:
- Identify the four types of weather fronts
- Recognize the type of weather depending on which front overtakes the other