by ZAMG
In the three-hourly sequence the first sign of a cloud intensification area is over Germany, where there are already many thunderstorms. By 18.00 UTC the intensification moves eastward and a distinct cyclonic curvature develops in the cloudiness. At the same time thunderstorm activity still increases, persisting until around 00.00 UTC but becoming less numerous.
Another interesting phenomenon is the separation of the enhanced cloud part from the main frontal cloud band which can be seen best between 18.00 and 00.00 UTC. This separated part remains as a convective line and moves NE-ward to the Baltic States and White Russia, as shown on the 05/06.00 UTC image.
There is a pronounced jet streak parallel to the western edge of the frontal cloud band which crosses the front represented by the thermal front parameter TFP in the area of Austria - Slovakia. In the WV image some deviation between the Black Stripe and the model jet axis (zero line of shear vorticity at 300 hPa) can be observed over Italy and Austria.There are two main PVA maxima accompanying the frontal cloud band and the jet streak area:
04 July 1997/18.00 UTC - Meteosat WV image; blue: thermal front parameter (TFP) 500/850 hPa, yellow: isotachs 300 hPa, black: shear vorticity 300 hPa
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04 July 1997/18.00 UTC - Meteosat WV image; black: positive vorticity advection (PVA) 300 hPa, yellow: isotachs 300 hPa, black: shear vorticity 300
hPa
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