Sequence of weather: Rain amounts

Development Phase: 06 August 02/06.00 - 18.00 UTC

The period of 06 August 06.00 - 18.00 UTC marks the phase of the development of the Genoa cyclone and the start of its NNE movement: It can be regarded as pre-flood phase. Thunderstorms prevailm in the S. and E. part of the cloud features, but over Switzerland and W. Austria an extensive area of precipitation develops which gradually moves towards mid Austria.

Flood Phase: 07 August 02/00.00 - 08 August 02/12.00 UTC

There is extensive precipitation during the whole period in Upper and Lower Austria, in the Czech Republic as well as in E. Germany and Bavaria. Within the Alpine region (especially Austria) from 08/06.00 UTC a slight shift of precipitation to the W (Salzburg and Upper Austria) can be observed.

Thunderstorms develop during whole period but they mainly form in specific areas of the occluded cloud spiral:

• In the S: Italy and (later) Bosnia
• To the NE in Czech Republic
• And later: in Germany in the area of the old main ULL

Precipitation amounts in pre-flood and flood phase

In the pre-flood phase of 06 August, till about 12.00 UTC, the precipitation is limited to N. Italy and S. Austria; then suddenly very intensive precipitation amounts appear north of the Alps which have their peak at 18.00 UTC in W. Austria (Tyrol) and Bavaria. From then on precipitation amounts move to eastern parts of Austria (Salzburg, Upper and especially Lower Austria). During this phase precipitation also appears in the eastern parts of Bavaria. From 07 August 12.00 UTC till 08 August 06.00 UTC there are also remarkable amounts of precipitation in Hungary and Slovakia.

Relationship of precipitation with relevant parameters

The loops below show the relationship of weather events with relevant numerical parameters, such as wind fields and convergence. The first clearly demonstrates the enhancement of weather activity by Stau effects, the latter show the dramatic effect of convergence, with an intensity and duration seldom seen in other cases.

Wind fields at 850 and 500 hPa

At 850 hPa a closed cyclonic circulation can be observed from 06 August 06.00 UTC which leads to remarkable Stau effects over the northern boundary of the Alpine mountain massif, and later, over the mountains in Slovakia and Czech Republic. The intense rain events in the western Alpine region and over Bavaria are in accordance with this airflow.

During the period under discussion the centre of the cyclonic rotation moves from SE Austria and W. Hungary to the east across N. Croatia and Jugoslavia to Romania. Consequently the whole area of the Czech Republic and N,NE Austria is under a N to NE stream which produces the Stau effects over the Czech and Alpine mountains.

From 06 August 06.00 UTC a closed circulation at 500 hPa can be observed which creates intense Stau effects. The eddy at 500 hPa moves from S. Austria and Slovenia to S. Hungary and then to the SE. Consequently, the Czech Republic and N, NE Austria come under the influence of an E to SE stream which turns to a N, NE stream over Austria from 07/12.00 UTC.

Fields of Divergence at 850 and 700 hPa