What happens if the warm air in front of the cold front is particularly dry?

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, close to the ground, like a snow blower, it glides 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 usually runs from northeast to southwest and can stretch for hundreds of miles, including large areas of land.

Before the typical cold front passes, there will be cirrus clouds or towering cumulus clouds, and cumulonimbus clouds may also appear. Due to the rapid development of clouds, showers and haze are also possible. The wind from the south or southwest urges 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 will 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. When the cold front passes, the rapidly decreasing atmospheric pressure 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 still 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 behind the actual front. The friction between the ground and the cold front hinders the movement of the cold front, resulting in a steep front. The result is a very narrow weather belt, concentrated in the front 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 towards the approaching cold front, the pilot can better understand the different types of conditions that will be encountered during the flight. Figure 10-27 shows the flight from Pittsburgh, Pennsylvania to St. Louis, Missouri.

When flying out of Pittsburgh, VFR weather was 3 miles of smoke and 3,500 feet of scattered clouds. 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 air pressure is dropping. As we approached Indianapolis, the weather deteriorated to 1000 feet, covered with clouds, with visibility of 3 miles, thunderstorms and heavy showers. In St. Louis, the weather improved, the clouds dispersed at a height of 1000 feet, and the visibility was 10 miles.

The pilot makes a reasonable judgment based on his knowledge of the situation ahead, and he is likely to stay in Indianapolis until the front passes. It is dangerous and foolish to try to fly under a thunderstorm belt or squall line. Don't try to fly over its top or around a storm. Thunderstorms can extend upward, far beyond the capacity of small aircraft, and may extend for 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 faster than the warm front, which moves at a speed of only 10-25 miles per hour. The cold front also promoted the formation of steep slopes. Strong weather activity is related to the cold front, and the weather usually appears along the front boundary, not in front. However, squall lines can form in summer months as far as 200 miles in front of a severe cold front. On the contrary, the warm front produces low cloud curtain height, low visibility and rainfall, while the cold front produces sudden storms, gusts, turbulence, and sometimes hail or tornadoes.

Cold fronts come quickly with little warning, and they can cause a complete change in the weather in a few hours. After that, the weather soon cleared up, and the dry air with unlimited visibility replaced 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. Generally, the cold front moves from south to southeast (for example, the cold front in Inner Mongolia passes through our province and slowly presses south from northwest to southeast). Before the influence of cold front, southeast wind or southwest wind usually 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 originally controlled by warm air, and the temperature dropped, the air pressure rose and the weather turned fine.