EUMeTrain

1st July 2004: 06UTC
The high gradient of the isolines manifest the frontal area. Two parts show a deeper downward intrusion of stratospheric air.

1). Behind the frontal system over the Northsea.

2). Over northeast Germany and Poland, which is an area where a double structure in the frontal system can be observed. Although from the field of temperature advection this part shows up as Warm front sector this is not supported by the appearance of cloudiness in satellite images nor by the height of PV=1 discussed here. The latter would rather diagnose an older cold front system

1st July 2004: 12UTC
As before, the isolines show a high gradient in the frontal zones and areas with some weak PV anomalies over south Sweden and the Baltic sea as well as over the eastern Baltic Sea. Both areas are connected to cyclogenesis but are not the area of the future Wave development.

1st July 2004: 18UTC
At this point in time the IR image shows the first indication of a wave bulge at the German-Polish border. Relevant for this development is the area over Southern Germany where a small scale anomaly can be observed. This indicates that cyclogenesis is supported by processes from above. However, at the same time also in the surface fields distinct height minima can be found.

2nd July 2004: 00UTC
In the satellite image the cloud bulges '1' and '2' can be identified separately. The height of PV=1 however shows completely different features. The northern Wave '1' is rather situated in an area of a high gradient of height of PV=1. The southern Wave '2' is immediately east of a PV anomaly over Poland. From this configuration one can conclude that this latter wave has developing potential.

2nd July 2004: 06UTC
The PV anomalies over Poland and White-Russia have clearly become more distinct during the past 6 hours. Stratospheric air has protruded downward to 500 hPa. A clear indication to further development!

2nd July 2004: 12UTC
The situation for Wave '2' has not changed. The features still are indicative for further cyclogenesis, PV=1 unit is down till 450 hPa.

The indications for a second Wave over western Austria is also worth noticing. Over Germany a small scale anomaly can be recognized. This gives a good indication for a possible further development.

2nd July 2004: 18UTC
A very distict intensification of the PV anomaly is shown in this image. It is at this point in time that the Wave bulges '3' and '3a' over Slovakia and Austria appear. The NE-ward protrusion of the dry air across west and north Austria is impressive and at the same time the PV anomaly widens, but does not deepen. Nevertheless, this is a very typical situation for the release of cyclogenesis by upper level features. Convective cells can be seen in IR imagery, indicating the convective development by overrunning stratospheric air with high values of PV and (not shown here) PV advection.

3rd July 2004: 00UTC
The development of convective cells and the influence of PV and PV advection have continued over the past six hours. The most convective cells can be observed over Slovakia. For the wave bulge marked by '3a', a PV anomaly over Eastern Austria is important. This is a clear indication for a release of cyclogenesis from above.

3rd July 2004: 06UTC
Both features discussed prior can be observed in this image as well. The increasing convectivity and the downward movement of stratospheric air. Thus the PV anomaly and the further development of Wave '3a' are enhanced.

3rd July 2004: 12UTC
The PV anomaly is protruding downward. Stratospheric air can be found at 450 hPa. At this point of time the low layers do not yet show any sign of a low pressure system. Satellite imagery and upper air features such as Isotachs and PVA 300 hPa, and the height of PV=1 give the only indication for a further development. As already mentioned before WA at 700 hPa gives an indication that at this point of time cyclonic rotation has already reached middle levels.

3rd July 2004: 18UTC
The same statements are true for this point of time which is 6 hours later.

4th July 2004: 00UTC
Another six hours later the level of cyclogenesis has increased dramatically. Stratospheric air has protruded downward to 550 hPa. At this point of time the lowering of the cloud tops (also discussed in IR imagery) is in accordance with this deepening.

Height of PV=1