Surface Observations

1st July 2004: 18UTC
Within the frontal cloud band different areas can be separated. There is:

1) Convectivity with thunderstorms along the leading part of the frontal cloud band from Southern-Italy to South-East Poland.
2) Rain is mainly found in the Alpine area of Austria and the Czech Republic.
3) Many thunderstorms are reported at the rear of the frontal cloudband in the area which reveals some indication of the development of a Wave.

2nd July 2004: 00UTC
The probable Wave areas over the Baltic Sea and Western-Latvia show precipitation reports but there are not yet concentrated to these areas. Over Poland in the area of the wave 2 the cloud bulge is free of precipitation which indicates only higher cloud.

2nd July 2004: 06UTC
Now the frontal cloud band and the wave bulge area around '2' are accompanied by widespread precipitation.

2nd July 2004: 12UTC
The Northern Wave '2' over Eastern-Poland and White Russia is weather active with reports of rain in the more frontal cloud part and thunderstorms in the comma spiral.

The area of cloud intensification in Austria marked by '3' is as before accompanied by extended rain. One of the reasons for this might be the orography of the Alps - but as already mentioned in the discussion on satellite images a Wave development might not be excluded. It is worth mentioning that in this area the main precipitation is in the cloud band, while the Northern part of the cloud is precipitation free. This would be in accordance with high clouds of the rear of the frontal cloud band.

2nd July 2004: 18UTC
Three Conceptual Models can be identified from this satellite image.

1) The Wave area '2' especially the substructure '2a' is still accompanied by some reports of precipitation.

2) The intensification area around '*' typically shows a thunderstorm but for the rest is not so weatheractive.

3) The Wave area in '3' and '3a' being quite distinct in the image, shows intensive reports of rain. The rearward cloud part of the wave bulge however, is precipitation free.

3rd July 2004: 00UTC
During night the precipitation activity becomes weaker. Wave '2a' only shows minor reports of precipitation. This is also true for the area of intensification '*'. Wave '3a' which will be of main interest during the next few slides, seems to consist of a precipitation area in Croatia and a huge precipitation-free cloud bulge. Such a development phase was not observed in Wave '2'.

3rd July 2004: 06UTC
Now in the area of wave '2a' precipitation reports have increased again. Also for wave '3a' the number of reports of rain have increased and the area of appearance has widened. In the whole cloud bulge reports of rain are numerous.

3rd July 2004: 12UTC
There is still widespread precipitation in Wave '3a'. Very impressive, although not directly related to the Wave, are the numerous reports of thunderstorms in the Cold Air over Central Europe.

3rd July 2004: 18UTC
The very impressive cloud bulge of Wave '3a' is also further accompanied by rain. Apart from the increase of the cloud bulge, no change in the weather activity has taken place in the last 18 to 21 hours.

4th July 2004: 00UTC
Now - as already mentioned in the discussion on satellite imagery - the dissolution of clouds from above (marked by '*') indicate a rapid development of the Wave area. This is reflected by the “no-rain” reports in that cloudpart, which in IR represents the warmer cloudtops.

4th July 2004: 06UTC
This is very typical; rain in the cloud spiral and no-rain in the low top frontal cloud band to the South.

4th July 2004: 12UTC
During daytime the convectivity increases and therefore also thunderstorms at the rear side of the cloud spiral. This feature will be also very interesting to study with the fields of PV and PVA.

4th July 2004: 18UTC
There are still reports of precipitation in the relevant area. Only the outermost part of the cloud spiral does not show precipitation reports.