Meteorological Physical Background

The most typical feature in many cases is a sinking dry intrusion from behind. It splits into two branches over the rearward and middle part of the cloud band of the CF in CA: one branch is oriented to the south-southwest and the other branch to the north-northeast. The southern part is sinking from high levels to middle or even low levels, whereas the northern part stays on high levels. This feature is not always clear, however, especially in the earlier stages of development. The warm conveyor belt is usually weak.

The great majority of CF in CA's are either weakening or remaining the same as they are. This is because the strong cold advection triggers the weakening of the fronts.

In the summer the CF in CA's may be accompanied by MCS development on the leading edge of the cloud band (see Convective Cloud Features in Typical Synoptic Environments: At the Leading Edge of Frontal Cloud Bands ). This is due to the unstable stratification caused by the warm conveyor belt below and cold dry intrusion above. This development occurs regularly in the area of northern Adriatic Sea, where the topography is further contributing to the instability.

On the 3rd of September 2007 at 00 UTC there is a Cold Front in Cold Advection reaching from Southern Sweden to the English Channel. The relative streams at 316 K show a dry intrusion coming from the cold, dry northern air and splitting over the frontal cloudiness into two branches: one is turning to follow the cloud band towards the northeast, while the other turns to southwest while sinking.

03 September 2007/00.00 UTC - Meteosat 8 IR10.8 image; magenta: relative streams 316K, yellow: isobars 316K