Interactive overlays: 17 Nov 2004, 12 UTC

The relevant development in this case study has its origin in the South of Greenland. Main features in the first IR image are two low pressure systems. One can be found to the north of Great Britain and is characterized by pronounced cloudiness on both fronts. The second system is situated in the South of Greenland.
On its back side the cyclone over northern Europe advects cold air from northern areas to the South while the system south of Greenland intensively advects warm air on its foreside to the North. This is the basic constellation of the upcoming development, which is strongly associated with the increasing temperature contrast and upper air processes.

This WV image shows wide areas of high cloudiness. These areas are associated with the low pressure systems over northern Europe and south of Greenland. The area between these systems represents the polar front zone.

The large low pressure system over northern Europe is represented well by the isobars at 1000 hPa. Its surface low is accompanied by a weak upper air trough. To the South, coinciding with the East-West oriented broad cloud band the 500 hPa lines are crowded. This is the region of the forming wave which leads to the rapid cyclogenesis. A strong gradient of the 500 hPa lines indicates high wind speeds in upper levels.

The isotachs in 300 hPa mark the position of the polar front. Wind speeds up to 70 m/s are reached. A strong maximum of PVA is connected with the low pressure system between Great Britain and Scandinavia. Other PVA maxima in the West are connected with the second dominant low pressure system.

A strong advection of warm air can be found in the warm sector and the warm front band of the low pressure system over Scandinavia. The second low pressure system to the south of Greenland advects warm air to the North on its foreside. The North Atlantic is characterized mainly by cold advection at this time.

A PV maximum on the backside of the low pressure system over Scandinavia can be seen. The polar front is indicated by a strong gradient of the isolines.