29th May 2005: 00UTC
In this chapter the IR images are overlayed with the Showalter index. It gives a good indication where the atmosphere is unstable and where convective development may be expected. Showalterindices between 1 and 4 give the indication that thunderstorm are possible but that a trigger is still needed. From this treshold the chance on thunderstorms increase. Values under –3 are associated to very heavy thunderstorms. In this set of images the treshold of Showalter Index = 0 is pictured using the pink line. This allows an easy discrimination of the potential convective areas. Such an area can be seen here stretched over central Europe. Ahead of the frontal system and further to the east over Greece and Turkey an area with Showalter Index smaller than zero is found. Over Spain and further south, embedded in the front the atmosphere is unstable with SI < 0.
29th May 2005: 06UTC
Ahead of the frontal system and also further eastward over Greece and Turkey areas with Showalter Index below zero are found. Over Spain and further south, embedded in the front the atmosphere is unstable with SI < 0. Also just south of the Alps the Showalter Index gives even lower values of –3.
29th May 2005: 12UTC
Except for some part containing the Black Sea most of Europe is within an area with Showalter Index under 0. Parts of Turkey and Bulgaria are even under –3 and therefor its not a surprise that in satellite imagery these areas are covered by numerous convective cells.
29th May 2005: 18UTC
Except for some part containing the Black Sea most of Europe is within an area with Showalter Index under 0. Parts of Turkey and Bulgaria are even under –3 and therefor its not a surprise that in satellite imagery these areas are covered by numerous convective cells. Also the area on the leading side of the frontal band shows a Showalter Index under –3. It is in this region that within the next 6 hours a huge MCS develops.
30th May 2005: 00UTC
Ahead of the frontal system the Showalter Index shows values below 0 and on some part even under –3. The area is potentially unstable and during nighttime some convection may again arise. Further to the east over Turkey, most of the CBs have died out. The area however is still unstable and developments of more CBs may still be accounted for.
30th May 2005: 06UTC
On the leading edge of the frontal system the Showalter Index shows values below 0 and on some isolated part even under –3. The area is potentially unstable and on day break with daytime convection it is likely to expect several TS in this area. Further to the east over Turkey, most of the CBs have died out over night. The area however is still unstable and developments of more CBs may still be accounted for as day advances.
30th May 2005: 12UTC
Within the large region with Showalter Index below 0 two seperate areas are recognised that even show lower values. Over Turkey the SI is below –3 and in satellite images numerous convective cells are recognised. In an earlier chapter we already related these to the surface observations which showed on a large scale thunderstorms. On the leading edge of the front a second area with SI under –3 is seen. It is in this area where in the following hours the large supercell over Poland and the two MCSs over Czech Republic and Austria will develop. All these event were next to thunderstorms also related to reports of hail which devasted crops and caused considerable material damage as well.
30th May 2005: 18UTC
Within the large region with Showalter Index below 0 two seperate areas are recognised that even show lower values. Over Turkey the SI is below –3 and in satellite images numerous convective cells are recognised. In an earlier chapter we already related these to the surface observations which showed on a large scale thunderstorms. On the leading edge of the front a second area with SI under –3 is seen. A large supercell over Poland and two MCSs over Czech Republic and Austria developed within the last hours. All these event were next to thunderstorms also related to reports of hail which devasted crops and caused considerable material damage as well.
31st May 2005: 00UTC
Most of the convection has died over the past few hours. The area is still highly unstable with SI values below 0, and on some parts even under –3. In the past few images it became clear that the Showalter Index in relation to satellite images is an effective tool to identify potential areas where thunderstorms are likely to occur
