What is quasi-static frontal weather?

The cold and warm air masses on both sides of the quasi-static front often form a "confrontation" state. The warm air mass was blocked by the cold air mass and forced to slide along the front. The situation is similar to the warm front, and the cloud system looks roughly the same as the warm front. Because the slope of the quasi-stationary front is smaller than that of the warm front, the warm air sliding along the front can extend away from the front, so the cloud area and precipitation area are wider than that of the warm front. However, the intensity of precipitation is small and the duration is long, which may cause continuous rainy weather.

Quasi-static frontal weather is generally divided into two types: one is the development of cloud system on the front with obvious precipitation. For example, the quasi-static fronts in South China are mostly formed by the weakening of cold fronts. The weather is similar to the first kind of cold front, except that the front slope is smaller and the cloud area and precipitation area are wider. The precipitation area is not limited to Feng Yu area, but can extend to a large area behind the front, and the precipitation intensity is relatively small, which is continuous precipitation. Because the quasi-static front moves slowly and often swings back and forth, the rainy weather lasts for ten days to half a month, or even more than a month. "It rains in succession during the Qingming Festival" is a portrayal of this kind of weather in the south of the Yangtze River. This rainy weather will not clear up until the quasi-stationary front becomes a cold front or the warm front moves out of the area or the front disappears. In early summer, if the humidity of the warm air mass increases and the lower layer heats up, the air layer may be unstable, and cumulonimbus clouds and thunderstorms may also form on the front.

The other is the development of the main cloud system under the front, and the quasi-static front without obvious precipitation. For example, the quasi-static front in Kunming is in a static state because the cold air heading south is blocked by mountains, and the warm air on the front is dry and slowly rising, which can't produce a large range of clouds and precipitation, while the cold air under the front slides up the hillside and is mixed with turbulence, which can form a nimbostratus under the front, often accompanied by continuous precipitation.

The quasi-static fronts in China mainly appear in South China, Southwest China and the north side of Tianshan Mountain, mostly in the winter half year, which has a great influence on the weather in these areas and their vicinity.