Airmass RGB Time Sequence: 3h, 29 February to 01 March 2008     

The stratospheric air (pinkish colour) was overrunning the frontal cloud field in the area of the Warm Conveyer Belt near the occlusion point at around 60°N and 20°W. The jet is clearly to be seen between Newfoundland and the region south of Iceland (transition from blue to violet/purple). This jet crossed the frontal cloud area (transition from whitish to pinkish cloud area). The centre of Emma was in the left exit region of the jet and under positive vorticity advection. The cloud head and a second jet can be identified south of Iceland and the north coast of Iceland, respectively.

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The clouds of the Warm Conveyer Belt overrun by stratospheric air and the jet is very clearly to be seen almost to the east edge of the frontal cloud system.

Emma intensified. Northwest of Scotland we recognise the onset of a split front.

Emma was now northwest of Scotland. The low clouds of the split front can be seen near the Scotish coast and over the northern parts of Scotland. The corresponding model radio sounding reveals the high humidiy in low levels (up to 600 hPa) and dry air aloft. This indicates potential instability.

Near Scotland convection started. The trough's axis for 300 hPa height arrived in the meanwhile the coast of Scotland (see also the corresponding image). At its east edge positive vorticity advection happened that fits also well with the left exit of the jet streak (corresponding image).

All structures moved to the East. We clearly see the dry slot over the North Sea (between Scotland and German coast).

All structures continued moving to the east/southeast.

It makes sence to zoom the relevant area in order to see more details. The zoomed image reveals the onset of a convective line between the purple area and the south edge of the blueish-violet area south of it. The latter marks the the rear edge of cold front whereas, north of it, the left exit region of a jet (corresponding image) caused positive vorticity advection. This PVA in connection with potential instable air caused first convection. The pinkish to orange coloured clouds give a hint of dry startospheric air above humid air in lower levels. This area extended already near Berlin.

The convective line is clearly to be seen and was just hitting the German coast.

The systems moved very fast to the southeast (about 100 km/h). The cold air extended from the Netherlands over North Germany to the east. The convective line was separated by a small zone of less cloudiness and can be seen over the northern parts of the Netherlands and Germany. The convective line was at the edge of a PV-maximum and positive vorticity advection. (The PV maximum moved to the south-southeast.)

At this time the structures were best to be seen. The cold front extended from the Baltic Sea to northern France. The convective line (separated by a small zone of low cloud amounts) is clearly to be seen. It extended over more than 1000 km from South Sweden to West Germany / East France.

All systems moved fast to the Southeast. The general situation did not change significantly. All structures are clearly to be seen. The corresponding images of wind in 300 hPa reveals the convective line in the left exit region over Middle Europe. The convective line is just east of the the sharp trough's axis. The convective line is southeast of the approaching PV-maximum in 310 K. The intense weather situation can be seen from the lightning detection (12942 lightnings within one hour, velocity about 100 km/h).

All systems moved fast to the Southeast. The general situation remained similar

In the meanwhile the cold front arrived the northern parts of Italy and former Jugoslavia. we see some lee clouds (due to Föhn effects of the Alps) over North Italy (bright blueish to white cirrus clouds).

All systems moved fast to the southeast. we still see the lee clouds that are far separated from the Alps (due to the high wind speed in upper levels, 100 to 150 kt in 300 hPa).

The convective line is less clearly to be seen.

The cold front arrived the line Baltic states Greece to North Africa.