Cold front weather system

When the cold air mass and the hot air mass intersect, a front is formed. If the hot air mass enters the cold air mass, it is called a hot front, otherwise it is called a cold front. The movement of the front will bring strong winds and changes in temperature and pressure.

cold front

When a cold, dense and stable air mass moves forward to replace a warm air mass, a cold front appears. The cold front moves faster than the warm front, moving at a speed of 25 to 30 miles per hour. However, the moving speed of the extreme cold front is recorded as 60 miles per hour. The typical cold front moves in the opposite direction to the warm front. Because of its high density, it is very close to the ground, just like a snow blower, sliding in warmer air, forcing the non-dense air to rise. The rapidly rising air causes a sudden drop in temperature, forcing the formation of clouds. The type of cloud generated depends on the stability of the warm air mass. The cold front in the northern hemisphere is usually from northeast to southwest, which can stretch for hundreds of miles and contain a large land area.

Before a typical cold front passes, there will be cirrus clouds or towering cumulonimbus clouds, and there may also be cumulonimbus clouds. Due to the rapid development of clouds, showers and haze are also possible. Winds from the south or southwest promote relatively cold air to replace warm air. The dew point is high and the air pressure decreases, indicating that the cold front is about to pass here.

With the cold front passing, towering cumulonimbus clouds or cumulonimbus clouds still dominate the sky. Depending on the intensity of the cold front, heavy rain may be accompanied by lightning, thunder and/or hail. A more severe cold front may also produce tornadoes. When the cold front passes by, the visibility will be poor, the wind direction will be changeable, there will be many gusts, and the temperature and dew point will drop rapidly. The atmospheric pressure, which drops rapidly when the cold front passes, will drop to the lowest point and then gradually increase.

After the cold front, the towering cumulus clouds and cumulonimbus clouds began to dissipate into cumulus clouds, and the corresponding precipitation also decreased. Finally, the visibility became very good, and the west wind or northwest wind prevailed. The temperature is colder, but the atmospheric pressure continues to rise.

Fast moving cold front

The fast moving cold front is driven by a strong air pressure system far away from the actual front. The friction between the ground and the cold front hinders the movement of the cold front, so a steep front is produced. This leads to a very narrow weather area, which is concentrated at the front end of the front. If the warm air overwhelmed by the cold front is relatively stable, the sky may be cloudy and rainy some distance ahead of the front. If the warm air is unstable, scattered thunderstorms and showers may form. A continuous thunderstorm rain belt or squall line may be formed along or before the front. The squall line is a serious danger to pilots because of the strong intensity and fast moving speed of violent thunderstorms. After a fast-moving cold front, the sky usually clears up quickly, and the cold front will leave violent gusts and colder temperatures.

Fly to the approaching cold front

Like warm fronts, not all cold fronts are the same. By checking the flight near the cold front, pilots can better understand the different types of situations they will encounter in flight. Figure 10-27 shows the flight from Pittsburgh, Pennsylvania to St. Louis, Missouri.

When flying out of Pittsburgh, VFR weather is smoke with visibility of 3 miles and scattered clouds at an altitude of 3,500 feet. When flying west until Columbus finally approached the cold front, the clouds showed signs of vertical development, with a fault of 2500 feet. Visibility in the smoke is 6 miles, and the atmospheric pressure is dropping. As we approached Indianapolis, the weather deteriorated to 65,438+0,000 feet and was covered with clouds. Visibility is 3 miles, with thunderstorms and heavy showers. In St. Louis, the weather is getting better, the clouds are scattered at an altitude of 1000 feet, and the visibility is 10 miles.

Based on the knowledge of the front, using reasonable judgment, the pilot may stay in Indianapolis until the front passes. It is dangerous and foolish to try to fly under a thunderstorm belt or squall line without flying over its top or around a storm. Thunderstorms may extend upward, completely beyond the capacity of small aircraft, and extend in bands of 300 to 500 miles.

Cold and warm fronts is in contrast

The characteristics of warm front and cold front are very different. The same thing is that every front is dangerous. Their speed, structure, weather phenomena and forecasts are all variable. The cold front moves at a speed of 20 to 35 miles per hour, which is very fast compared with the warm front, and the moving speed of the warm front is only 10-25 miles per hour. The cold front also promoted the formation of steep slopes. Severe weather activity is related to cold front. However, squall lines can form in summer as far as 200 miles in front of a severe cold front. On the contrary, the warm front will produce low cloud curtain height, low visibility and rainfall, while the cold front will produce sudden storms, gusts, turbulence, and sometimes hail or tornadoes.

Cold fronts come quickly with little warning, and they can completely change the weather in a few hours. After passing through, the weather will clear up quickly, and the dry air with unlimited visibility will replace the original warm air. On the other hand, the warm front provides an early warning for their arrival, and it may take several days to pass through an area.

In autumn and winter, we often hear "cold front crossing the border …" in the weather forecast. What is a cold front? According to experts from the Provincial Meteorological Observatory, the interface formed by different cold and warm air masses is commonly known as "front". Near the front is the intersection of cold and warm air, so the meteorological elements here change dramatically, often accompanied by clouds, precipitation, thunderstorms, strong winds and other weather phenomena. In the process of moving, the cold air mass plays a leading role, and the front that pushes the front to move to the side of the warm air mass is called the cold front.

The frequency of cold front crossing is the most frequent in winter. The cold front generally moves south to southeast (for example, this time the cold front in Inner Mongolia passes through our province and slowly presses south from northwest to southeast). Before the influence of the cold front, the southeast wind or south to southwest wind generally blows, and the air pressure decreases, the humidity increases and the temperature is higher; Affected by the cold front, the wind turns north, the air pressure gradually increases, the humidity decreases, the temperature drops, and precipitation generally occurs; After the cold front, cold air gradually occupied the area controlled by warm air, the temperature dropped, the air pressure rose and the weather turned fine.