cold and warm fronts

Cold front is the most common front in China, and it can move all over the country. However, due to the different configurations and moving speeds of the cold front and the upper trough, the distribution of clouds and precipitation near the cold front is also obviously different, and some mainly appear behind the front; Others mainly appear in the front.

According to the analysis of meteorologists, the weather conditions of cold front can be roughly divided into two types:

The first type: the cold front moves slowly and has a small slope, which is in front of the 700 HPA trough in the air, and is usually called the first type of cold front. This type of cold front, because the cold air mass moves forward on the one hand, makes the warm air mass in front of the front move forward on the one hand, and is forced to slide upward along the front on the other hand. When the water vapor condition is sufficient, cloud system and precipitation will be generated on the front.

Because this cold front is in front of the high-altitude trough, it is conducive to the upward movement of air. Before the front came, the warm air mass was not blue and cloudless. With the arrival of the cold front, there are often cirrus clouds and cirrostratus in the air. As the front approaches, the clouds gradually thicken. The frontage is nimbostratus, and the width of rain area is about 150~200 km.

The second type: the cold front moves quickly and has a large slope. It is often called the second type of cold front behind the trough at 700 HPA or near the trough line. The cold advection above this cold front is strong and the airflow sinks. Only the warm air near the ground front is lifted, but the front has a large slope and a strong airflow moves upward. The weather conditions in winter and summer are obviously different. In summer, the warm air mass is moist and unstable, and the strong cold advection on it becomes more unstable. Therefore, strong cumulonimbus clouds often form near the front line and are arranged near the front line like a cloud embankment. When the cold front comes, there will be thunderstorms and formation precipitation, but the rainfall area is only a few tens of kilometers. In winter, warm air before the front is located in front of the trough, and the airflow rises to form cirrus, cirrostratus, high-level clouds and nimbostratus. Near the ground front, there is a vast continuous precipitation area. After the precipitation stops, there is often a strong wind, also called a dry cold front.

Because the cold front moves fast and slowly, when the cold front moves slowly, the warm air will rise slowly and steadily, so it is easy to appear layered clouds and the rainfall is moderate. When the cold front moves fast, warm air will be lifted rapidly by cold air, which is easy to cause heavy cumulonimbus clouds, accompanied by lightning and heavy rain.

Occurrence time: there are cold fronts in northwest China all year round, strong in winter and weak in summer, with similar frequency. Its shape and moving speed are greatly influenced by the terrain.

The general characteristics of cold front activity: there is cold front activity in East Asia. The frequency of cold front is more in the north than in the south, and the frequency of cold front in the southwest is the smallest. Half a year in winter is more than half a year in summer, with the most in spring and the least in autumn.

Location: The intensity of cold front is strongest in winter, which often directly drives South China and South China Sea, resulting in cold wave weather. The cold front in summer is weak, mainly in the north, and it often brings thunderstorms.

North China is the only place for cold front activities in China. In Northeast China, there are cold fronts all year round, especially in spring and autumn. There are three sources of cold front in these two areas: West Road, Northwest Road and Beibei East Road. The cold front in winter mainly causes cooling and strong winds, and thunderstorms can occur in summer. In spring, cold fronts often cause strong winds and precipitation in Northeast China, but only sandstorms in North China.

After the cold front:

1 temperature: drop

The air pressure drops first and then rises.

Precipitation: There is rain behind the front.

When the front moves, if the warm air mass plays a leading role in pushing the front to move to the cold air side, this front is called a warm front. In China, the warm front often appears on the east side of cyclone center, and it often appears in pairs with the cold front. Generally, when a warm front passes through the boundary, the air pressure decreases and the temperature increases.

warm front

warm front

In the process of front movement, if warm air plays a leading role in pushing the front to move to one side of the cold air mass, this front machine is called warm front. After the warm front crossed the border, the warm air mass occupied the position of the original cold air mass. Warm fronts are mostly active in northeast China and the middle and lower reaches of the Yangtze River, and are mostly accompanied by cold fronts. After the warm front crossed the border, the temperature rose, the air pressure dropped, and the weather turned cloudy and rainy. Not a cold front.

Warm front weather patterns

In the cold air mass under the warm front, stratocumulus and cumulus are often produced under the action of airflow convergence and turbulence because of the humidity of the air. If the raindrops falling from the front warm air evaporate in the cold air mass, the water vapor content in the cold air mass will increase, and when it reaches saturation, cumulus clouds and stratocumulus clouds will be produced. If this saturated condensation occurs in the ground layer near the front line, frontal fog will be formed. The above is the general situation of warm front weather, but when the warm air is unstable in summer, there may be showers such as cumulonimbus clouds and thunderstorms. When the water vapor content in the warm air mass is very low in spring, only some high clouds appear and there is little precipitation.

There are few obvious warm fronts in China, and most of them are accompanied by cyclones. In spring and autumn, it generally appears in the Jianghuai Basin and Northeast China, and it mostly appears in the Yellow River Basin in summer.

The low pressure forms a cold front, and the weather is fine under the control of high pressure. It can't be said that they are related, and it can't be said that they are completely unrelated! Because there are integrity and differences between geographical environments.