Frontal System across Europe with Wave Development - Case Study 12 - 13 November 1997

• I. Synoptic Situation for 12 November 06.00 UTC
• Overview and frontal diagnosis
• Wave development in the area Sardinia - Corsica
• Intensification of frontal cloudiness and activity by jet streak crossing
• Cloudiness over Italy and the Balkan peninsula in front of the Cold Front: Relative Streams
• II. Development During the next 12 Hours
• Frontal displacement with help of the Thermal Front Parameter
• Displacement of the Wave
• Front Intensification by Jet Crossing
• III. Synoptic Situation for 12 November 12.00 UTC
• Overview and new aspects
• Diagnosis of front and Wave(s)
• Relative streams: Cloudiness over the Balkan peninsula
• IV. Synoptic Situation for 12 November 18.00 UTC
• Comparison of cloud configurations between 12.00 and 18.00 UTC
• Overall situation and frontal diagnosis
• Relative streams
• V. Synoptic Situation for 13 November 00.00 UTC
• Introduction for 13 November 00.00 UTC
• Overview and frontal situation
• Relative streams: Frontal and pre-frontal situation
• VI. Development of Thunderstorms and MCSs During the Whole Period
• Introduction for the diagnosis of conceptual modles for convective developments
• The period 12 November 05.00 - 07.00 UTC
• The period 12 November 11.00 - 12.00 UTC
• The period 12 November 14.00 - 18.30 UTC
• The period 12 November 21.00 UTC - 13 November 00.00 UTC
• Some summarizing ideas

Relative streams: Cloudiness over the Balkan peninsula

12 November 1997/12.00 UTC - Meteosat IR image; position of vertical cross section indicated	12 November 1997/18.00 UTC - Vertical cross section; black: isentropes (ThetaE), orange thin: IR pixel values, orange thick: WV pixel values
12 November 1997/12.00 UTC - Meteosat IR image; black: shear vorticity 300 hPa, magenta: relative streams 311K - system velocity 230° 10 m/s, yellow: isotachs

In the bottom left image the different relative streams involved in the synoptic situation can be clearly separated on the ThetaE surface of 311K which is on top of the frontal zone:

• The Warm Conveyor Belt from south-east which is rising while turning to the north-east over the Balkan Peninsula; it is responsible for the development of the cloudiness there;
• The humid relative stream from the rear side of the front but on the anticyclonic side of the jet axis which can be found in the leading part of the frontal cloud band;
• The dry intrusion which is to a certain degree superimposed on the rearward part of the frontal cloud band at this time. The process of jet streak crossing seems to be the reason that at higher levels dry air overruns the southern parts of the frontal cloud band under sinking motion, especially in the area of Algeria and Tunisia. This will have serious consequences and will be followed in the later points of time.