Interactive overlays: 29th May 2005:00UTC

General information: 29th May 2005:00UTC
A small comparison with the surface analysis of the 29th of May shows that western Europe is governed by a frontal system. Over Spain some convective cells are embedded whereas further north over the Netherlands and Danmark the frontal band has more or less decayed (probably caused by NVA in right exit region, see jet cloud fibre over Atlantic). The Occluded part of the band is found north of Scotland over the Faroe Islands. On the leadinge edge of this front convective development will be seen in the following hours.
Over the Balkan region the remnants of some CBs are seen. Under influence of daytime convection more development will be seen here as well.

WV6.2
A frontal system is covering the Iberian Peninsula. Especially over Southern Portugal and Gibralta a large MCS embedded into this system is observed. In the thickness ridge on the leading side of this front other CBs are recognised. Over Greece and Albania some remains of CBs are seen.

Airmass RGB
In this airmass image the frontal system over Western Europe is easily picked up. The overrunning jet in the Occlusion part of the front causes these clouds to be identified as mid-level clouds (ochre). More interesting to this case however, is the belt of low pressure systems (see surface analysis 29th May. Low pressure is denoted by the capital ‘T’) found over Central and Eastern Europe. This belt can also be seen in the airmass images as the very dark blue coloured band over Egypt, Tunis, Italy, Austria, Slovenia and Romania. The cyclonic side of the belt is pictured in purple which gives a good indication on the deepening of stratospheric air at these places. Over Turkey, Greece and Bulgaria more deepening is observed, hence the red and purple colours. The deepening makes the atmosphere conditionally unstable and it is not a surprise that at later stage these will be the areas where most convective development is taking place.

Geopotential Height 1000 hPa
The occlusion of the frontal band is easily picked up by the surface low over the Shetland Islands. Central Europe is still experiencing fair summer weather with a large high pressure system superimposed. Over Albania and Greece a diffluent flow is experienced.

Geopotential Height 500 hPa.

Geopotential Height 300 hPa
Most striking is the pronounced upper level trough behind the frontal system. The axis of this trough lies over the Atlantic. Central Europe is still under influence of a high pressure system and nice weather. Over Turkey and Greece a low pressure area is seen. Already an indication to the weather it is going to bring.

Relative Topography
For the development over central europe the study of the equivalent thickness and the thermal front parameter can be of use. At this timestep the model reflects the frontal band over Western Europe well with several TFP maxima. On the leading side a thickness ridge is seen over Eastern Germany which gives an indication to future possible convective development. Over Turkey and Greece no frontal features are seen.

Thermal Front Parameter
For the development over central europe the study of the equivalent thickness and the thermal front parameter can be of use. At this timestep the model reflects the frontal band over Western Europe well with several TFP maxima. On the leading side a thickness ridge is seen over Eastern Germany which gives an indication to future possible convective development. Over Turkey and Greece no frontal features are seen.

Temperature Advection 700 hPa
In the image the frontal system can be recognised. It is superimposed with warm air advection. Further north the cold air advection behind the occlusion is also pronounced and nicely visible. Ahead of the frontal system an area with WA is seen over Switzerland and Austria. This in combination with the with the drier and colder air at upper levels (see "WV6.2 29-5-2005 00UTC") leads to potentially unstable stratification of the troposphere. Further to the southeast the remnant of some CBs is seen over Albania. They are under CA. The other region where convection will start is over Turkey and Greece which horizontal distribution reveals some WA. Also in the WV image some fine structures are seen there as well.

Height of PV=1
South of the Alps over Romania and the northside of the Black Sea a WV dark stripe can be observed. This is where deepening of stratospheric air up to 250 hPa is taking place. Further South some more fine structures can be seen in WV imagery. Deepening up to 300 hPa is associated. The boundaries of these WV and PV features are indicative for further convective development.

PVA 300 hPa

Isotachs 300 hPa

Showalter index
The Showalter index gives a good indication where the atmosphere is unstable and where convective development may be expected. Showalterindeces 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 underr –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 allow and 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.

ThetaE 850 hPa