Surface Pressure Tendencies, Time Sequence: 27 July 2006

The pressure tendencies' measurements refer to the last 3 hours and are displayed in units hPa/10. From 9 UTC till 12 UTC negative pressure tendencies (red) are found over most parts of Germany, typically in the forefield of a convergence line. West of this convergence we find rising surface pressure (blue, a so-called meso high). This 'dipole structure' is a hint for the onset or an intensifying direct thermal circulation, which leads rather often to a squall line (see surface analysis 12 UTC).

When we concentrate upon Germany, we see rather often stronger negative surface pressure tendencies near and in the forefield of convective cells (about -1.5 to -2.0 hPa / 3h) whereas west of these structures only low pressure tendencies or even positive values were reported.

Over western Germany we observe a North to South orientated area with small or even positive surface pressure tendencies. In contrast to that, further to the East the surface pressure decreased more rapidly.

In the front's forefield the irradiation continued whereas the central and rear part clouds reduced the irradiation and the precipitation caused an additional temperature decrease. These processes led to an increased horizontal temperature contrast at the front. We observe a clear dipole structure of falling and rising pressure at the frontal side and the central and rear parts (red negative and blue positive yielding typically a meso high).

The dipole structure becomes clearer at this timestep. The squall line exhibits its highest intensity that reveals very clearly in form of the dipole structure with decreasing surface pressure at the leading edge and positive pressure tendencies of more than 2 hPa/3h. The meso high in the rear of the squall line is now most intense. For additional information about the cloud top temperatures compare IR-Enhanced imagery 16 UTC.

This image shows a big area with increasing surface pressure (up to 2 hPa/3h) over central Germany, which covers mostern parts of the convective clouds whereas the negative pressure tendencies in the forefield of the squall line weakened. The squall line started decaying.

We see with a few exceptions that the big cloud area over Germany is superimposed by strongly increasing surface pressure yielding the further weakening of the convective processes.