Meteosat 8 composite: WV6.2-WV7.3; IR3.9-IR10.8; NIR1.6-VIS0.6

29th May 2005: 05UTC
The Severe Convection RGB, which is also discussed thoroughly in the MSG interpretation guide, is suitable for the detection of convection and it is able to discriminate between young and old convective cells.

The interpretation of the colours goes according to:

• red: Deep precipitating clouds contained of large ice particle
• yellow: CBs with severe weather and strong updrafts; small ice particles OR thick high level lee cloudiness.
• darkred: Thin cirrus; large ice particles
• purple: Thin cirrus cloud; small ice particles
• blue: Thin to no clouds.

With this information it can now be derived that the frontal band over Western Europe is consistant of high reaching clouds with a mixture of large and small ice particles. Over the Netherlands the frontal clouds seems to have dissolved a little as it is pictured in blue. Further north some activity (Thunderstorms and Rain e.g.) may be expected in Estonia. At this stage the first convectivity also starts in Bulgaria and southern Greece.

Note. You can always click on the to bring up the RGB-key.

29th May 2005: 06UTC
An increase in convectivity is seen over the Balkan region. Second interesting is the thin cirrus shield (purple) seen over Bavaria, Switzerland and Western Austria. The Alps themself are picture in darkred due to presence of snow.

29th May 2005: 0645UTC
In Greece a clear dicrimination between several CBs can be seen. The lightblue to green colours surrounding the cells suggests that there is more upper tropospheric humidity (UTH) availabe. The core of the cells is where the strongest updraft is found (smallest ice particles) the more away from the center, the updraft becomes less and as a result a more reddish appearance of the cell edges is observed.

29th May 2005: 08UTC
The development continues.

29th May 2005: 09UTC
The development continues.

29th May 2005: 10UTC
Immediately noticeable is the increase of convective cells over Turkey.

29th May 2005: 11UTC
Due to orographic lifting the first indication of new cells (yellow spots) over the Jura and Vogesen mountains in France is seen.

29th May 2005: 12UTC
Big MCSs can be seen over Bulgaria, northern Turkey and Eastern Turkey. Especially the MCS over Bulgaria saw some explosive growth over the past few hours (Compare!). Due to the large differences in temperature between land and water a line of CBs is recognised along both coastal areas.

29th May 2005: 13UTC
The development continues.

29th May 2005: 14UTC
In comparison to the IR10.8 image (see "IR10.8 29-5-2005 14UTC") several convective cells can easily be distinguished in the “Severe Convection RGB”. Whereas in IR one sees one big white spot over Bulgaria and Greece, with this RGB several separate cells are recognised. Over the southern coast of Turkey the daytime convection is reversed, and most cells are pictured in orange. These cells are dying out as one will see in the next few slides.

29th May 2005: 15UTC
The development continues.

29th May 2005: 16UTC
Over the Swiss and the Austrian Alps also some convection as seen. Due to orographic lifting some isolated convective cells can be recognised. In Eastern Turkey the convection becomes less. The color of the cells has changed from yollow into orange/red over the past hours. This indicates a change from small ice particles into larger ones. In Bulgaria and Greece most cells have "merged" into one big cell.

29th May 2005: 17UTC
That this RGB makes use of two visible channels (0.6 and 1.6 μm) becomes clear when observing the cloudiness over Turkey. Channel 1.6 act as a near infrared channel which especially in these situation of twilight will increase the amount of blue in this RGB (hence, blue is the BTD of 1.6μm – 0.6μm) which explains the purple colour. Over the Alps in Austria the convection seen previous has increased a little as a larger cell is recognised. At the leading edge of the frontal system now some cells can also be recognised. Near Reims and Nancy in Northern France.

30th May 2005: 05UTC
The second day of this case study. The Atlantic is still covered in darkness (hence the purple appearance) and the frontal system has shifted eastward covering Central France, the Benelux and Germany. Over Northwestern Poland a convective cell is spotted which developed overnight at the leading edge of the front.

30th May 2005: 06UTC
The development continues.

30th May 2005: 07UTC
Interesting to explain are the turqois colours seen over Estonia and Turkey. These come from the difference in humidity between the upper troposphere (moist) and the lower troposphere (drier). To the surface the first icing has already started explaining the great share of green.

30th May 2005: 08UTC
In Turkey first indication of convection is seen as several small cells are recognised.

30th May 2005: 09UTC
The development continues.

30th May 2005: 10UTC
The convective development over Rumania has continued. The cells have increased in size and appearance (more yellow).
In Central Turkey some large CBs are seen. Most convection however is seen along the coast. It is very likely that this convection will increase the next hours.

30th May 2005: 11UTC
As daytime convection gets underway several isolated CBs are recognised in Bulgaria, Sicily, Czech Republic and on the southside of the Austrian Alps.

30th May 2005: 12UTC
All the cells discussed previous have shown further development. Not only an increase in size but a brighter appearance (yellow) as a result of the severe updrafts. These cells are highreaching and consistant of small ice particles.

30th May 2005: 13UTC
The development continues.

30th May 2005: 14UTC
Over Rumania orographic lifting induced convection along the Carpathian Mountains (which contours can easily be witnessed).
The MCS system over Czech Republic and Austria are merging forming a supercell on the leading side of a front. Over Italy and Croatia several thunderstorms are observed. Also in Greece several isolated convective cells are seen. These cells will be studied using radar at a later stage of this case study.

30th May 2005: 15UTC
One huge MCS system now formed covering parts of Austria, the Czech Republic and parts of Poland. The MCS formed over the past few hours on the leading side of the N-S front over western Europe.
Part of Croatia, Albania, Greece, Bulgaria are also still covered by numerous convective cells.

Interesting is also the chain of convective cells which has formed over the border of White-Russia and the Ukrain and Russia. These probably developed as a cause of shear between the two dominant flows.

30th May 2005: 16UTC
As day almost ends in Turkey the level of convection of Turkey dies out as it appears more reddish in the satellite image (old convective cells with large iceparticles). Over the Balkan region and Central Europe several convective cells can still be observed. Most depicable in the image still remains the MCS system over Austria, Czech Republic and Poland. A very unusual feature can be seen over this last supercell whereby a plume of cloud appears to emanate from the cell and streams away in a northerly direction.

30th May 2005: 17UTC
The last image in these series. Most convection discussed and pointed at before can still be witnessed. As daytime convection is ending most cells over Greece appear as reddish indicating the increase of large ice particles in these highreaching clouds. On the Eastside of the supercell over central Europe the shadow on the earths surface can be seen quite clearly.