We know that air masses are huge atmospheric bodies within which there are different humidity and temperature conditions that characterize the type of air mass we are dealing with. These air masses adopt the characteristics of the area in which they are formed and depend on the movement they generate when they are created. According to the stability of the air masses we can find different types of fronts. Today we are going to talk about warm forehead and their characteristics.
If you want to learn more about the origins and consequences of a warm front, this is the post for you.
Air masses and atmospheric stability
To understand what a warm front is, we must know the atmospheric dynamics in relation to the functioning of the air masses. The stability of all air masses is what determines the weather that occurs in a certain area. When we have a stable air we speak of an area where movements are not allowed vertically. For this reason, the formation of precipitation clouds cannot occur. When there is atmospheric stability, it is very appropriate to speak of anticyclones. While stable air favors good weather.
On the other hand, when there is unstable air, we see that vertical movements are favored and rain clouds are produced with rough weather. These situations are associated with depressions since there is a drop in atmospheric pressure and the creation of a storm.
If an air mass circulates over a surface that is cooler, it is considered a warm air mass. Movement across the surface that has a lower temperature will begin to cool down the part closest to the ground. In this way, as the air on the surface begins to cool becomes denser and heavier. With this type of characteristics, vertical air movements are prevented, thus creating a stable air mass. This stability stands out for having weak winds, a vertical temperature inversion, which causes an increase in dust from the pollutants that exist in the lower layers. This stability is a problem for the most polluted cities. We also see some difficulties for full visibility and few clouds with vertical development.
On the other hand, if the air mass circulates over a surface that is warmer than it is called a cold air mass. As it circulates on the surface, the opposite effect to the one we have described will occur. It will begin to heat up at its base and they become less dense, which will favor vertical movements. This turns into an unstable air mass which causes an increase in the intensity of the wind, an improvement in visibility, but a development of clouds and precipitation.
Warm front
As we have already seen, air masses are characterized by similar temperature and humidity conditions throughout. That is why we must separate air masses by a discontinuity surface. Depending on the characteristics they have at the boundary of an air mass, we can see the formation of a warm front, a cold front, an occluded front or a stationary front.
A warm front forms when a warm air mass reaches a colder air mass. The warm air tends to rise over the lower air mass. This lower air mass is known as the cold front. When these air masses collide, condensation occurs and clouds form. The main characteristic of a warm front is its slight slope. That is, usually travels at an average speed of about 30 km / h and has a cloud cover height of approximately 7 kilometers. This means that the predominant clouds are low and medium clouds.
Clouds and precipitation develop along the contact surface between the two air masses. Between the appearance of the first clouds and the beginning of the precipitations can happen between 24-48 hours.
Warm front weather
Let's analyze the weather conditions a warm front brings. The atmospheric situation caused by a warm front begins with the appearance of high clouds. These high clouds are known as cirrus clouds. They are usually located at or near the front, about 1000 kilometers or more ahead of the front. A drop in pressure usually begins due to rising warm air and the retreat of cold air.
Progressively, we see how the sky becomes cloudy as it approaches the most important part of the unstable line. Cirrus clouds become in cirrostratus that thicken more and more to form altostratus. Depending on the instability of the front, it may add some drizzle during the formation of these clouds. We see that the pressure levels continue to drop and the wind speed increases. We know that the wind moves toward areas with lower pressure. Therefore, if there is a drop in surface pressure as warm air rises, the wind will move in that direction.
Finally, nimbostratus clouds appear. These clouds are located over the same front and are responsible for the most significant rainfall. The wind reaches its maximum intensity and the pressure continues to drop. Lower clouds such as strata These clouds are formed by increased humidity due to the precipitation generated. Some of these clouds are alone, which are responsible for hiding other higher clouds and generating frontal fog. Occasionally, This fog can give visibility problems to the horizon.
Fronts advance very weakly and usually produce light to moderate rainfall. The predominant characteristic of a warm front is that, although they may produce moderate to light rainfall, they affect a large area and last for a long period of time. These fronts are usually found in the colder months of late autumn or early spring, or during winter. At these times, precipitation may occur as snow, then gradually turn into sleet and eventually rain.
I hope that with this information you can learn more about the warm front and its characteristics.