Convective activity in Fair Weather Conditions results in the typical life cycle of convective cells like Cb - Cluster or MCS. The difference to other environments of convection can be found in the initial stage of the life cycle:

• In satellite images, convective cells are normally far away from frontal cloud bands as well as frontal circulations.
• In the IR and VIS images there are no significant pixel values within the affected area.
• In nearly all of the observed cases (about 40) the convection starts within the small stripe like area of the smooth transition zone between relatively high and low WV pixel values.

Appearance in METEOSAT imagery:

• IR imagery:
  • Only a few low pixel values or nearly black pixels during the initial stage
  • Developing Cb or Cb - cluster with high pixel values in a circular shape
  • In a more mature stage developed Cb, Cb - complexes and MCS can be observed
• WV imagery:
  • WV structures can be seen such ase eddies, vortices, filaments, stripes
  • Near a smooth transition zone between higher and lower WV pixel values, deep convection will be indicated by Cb's or a MCS
• VIS imagery:
  • as for the IR imagery, no significant cloud pattern can be observed during the initial stage
  • during the life cycle the growth of convective clouds can be observed

The satellite image loops above show an MCS development over Austria and Hungary. In the enhanced IR image, as well as in the other two satellite channels, the first cells can be identified at 10.00 UTC over the south side of the eastern Alpine ridge. In the WV image loop the first cell develops at the southern border of a WV eddy which is moving southward. Further cell developments occur within the transition zone from higher to lower pixel values (e.g. at the northern border zone more to the centre of the vortex). At later stages of development the merging of cells into an MCS can be seen.

In the VIS image loop multiple small convective developments over the Alpine ridge can be seen during the initial stage.

As has been described above, the WV boundaries are preferred areas for initiation of convection. The exact position where convection is triggered within this boundary seems to be determined by the orography.

The above image loop, of 5th May, shows the development of deep convection over SW Germany, the Czech Republic and N. Austria commencing at 10.00 UTC. Again the development starts within or next to the transition zone between higher and lower WV pixel values. MCS development soon follows. The satellite loop above shows some developing convective cells over the Hungarian - Romanian border commencing at 09.00 UTC. It can be seen that the cells grow from the WV boundary into the drier zone (WV Dark Stripe). By 10.00 UTC convective activity is taking place over the whole area of Central and Eastern Europe. The WV image loop above shows a large number of developing convective cells over Central and Southern Europe.