Radar PI (international composite) Time Sequence: 27 July 2006

The colours represent classes of measured reflectances in dBz (see legend).

Radar images are essential in diagnosing the strength of CB clusters in terms of precipitation amount and type (snow, sleet, hail). During summer only hail is relevant. A rough estimation for central Europe is that hail is possible for more than 56 dbZ (blue coloured radar pixels). The so-called PI product (international radar composite) represents reflectivities in about 2 km with a horizontal resolution of 4 km.

We will investigate the radar reflectivities in relation to the clouds in the IR image (compare also with chapter on IR-Enhanced imagery).

For more information see chapter 'Radar' in SatManu: Cumulonimbus (Cb) and Mesoscale Convective System (MCS) - Key Parameters.

The areas with high dBz values grew. However, we still see separate convective cells. In many cases we see again the highest reflectivities (blue and red pixels) in the western edge of the convective clouds

The merging of the convective cells as we saw in the chapters before (see Lightning 14 UTC and IR Enhanced 14 UTC can be seen also in the radar images. A close relation can be found between the new developments at the southern flank of the two big cells (over northwestern Germany and south of it). We see low cloud top temperatures which correspond well with high dBz values.

This image shows to some extent the shape of a squall line. From northern to southern Germany a sharply edged and roughly structured area of high dBz values can be observed (heavy rain or even hail). Farer to the West we recognize smoother fields of reflectivities that were connected to heavy rain after the thunderstorms passed (precipitation of up to 30 mm/h, not shown).
Again we see an excellent correspondence between very low cloud top temperatures (IR Enhanced 15UTC) and high dBz values (blue pixels). Also the Convective Storms RGB delivers valuable hints.

We clearly recognize a squall line structure (sharply bounded area). The clouds farer to the East were mainly in the middle and upper layer that can be concluded only from the combination between IR-image and radar (no reflectivity in radar image). Farer to the East (recently developed cells over Central/East Germany) the radar image reveals high reflectivities (47 to 56 dBz) equivalent to active convective cells.

The squall line structure remained during the last hour and high reflectities were still obtained (up to 56 dBz). Precipitation amounts of partly more than 10 mm/h were reported.

The squall line continued weakening. However, dBz-values of up to 56 and precipitation amounts of partly more than 10 mm/h were still measured.