Within the polar front theory no separation between cyclogenesis through a wave development and a rapid cyclogenesis can be found. The proceeses observed in this case study cannot be explained well by the polar front theory.
The jet streak and surrounding sinking dry air play key roles in this case study. The emerging cloud head in the initial stage usually appears in the left exit region of a jet streak. This correspondends well with the development observed in this case study.
The jet streak is parallel to the initial cloud band. Dry stratospheric air superimposes the cloud head. This is seen as the typical black stripe in the WV images as well as by the fields of PV, wich show a clear PV anomaly. While in a case of wave development stratospheric air (if present at all) does not reach down to levels lower than 300 hPa, in the case of rapid cyclogenesis stratospheric air is a key feature and protrudes much further downward (down to approximately 500 hPa or even lower).