In case of a Warm Front, warm cold warm air moves against warmer colder colder air. At the boundary of these two air masses the dry moist moist air tends to glide up over the wedge of dry moist dry air. This process causes the frontal cloud band, and therefore also gives an explanation on why most precipitation can be found in front of to the rear of in front of the surface front.

The main difference between a Warm front band and shield lies in the appearance in satellite imagery and in the vertical cross sections. In the vertical cross section it was two frontal zones could be seen with the Shield Band Shield type of Warm Front. Beside the surface front an extra upper level front could be observed. The diffence in cloudiness can best be explained by using the conveyor belt theory. The ascending descending ascending Warm Conveyor Belt starts just behind in front of behind the surface front in the lower levels of the stratosphere troposphere troposphere and has greatest upward motion in the boundary layer beween 700 and 500 hPa beween 700 and 500 hPa .
After it has crossed the surface front it can still rise up to the tropopause about 300 hPa about 300 hPa There the Warm Conveyor Belt turns and stops rising. If there is enough humidity rotation in the for of PVA humidity in the atmosphere, the result of this ascending Warm Conveyor Belt is condensation and higher cloudiness. With a WF Band there is usually not enough ascending motion condensation motion , which is one of the reasons that no cloudiness upper level front cloudiness develops. In the shield type the ascent is usually much stronger. If the frontal surface upper level front frontal surface is approached by the conveyor belt, then the isentropic surfaces become more and more inclined leading to a stronger ascent of the relative stream. This process can often be followed in satellite images by the development of cloudiness in the warm sector of a Warm Front band culminating in the formation of the complete cloud shield.

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