Frontal analysis

We concentrate on the area of frontal cloud bands stretching from Romania to Finland (H04).
The surface (1000 hPa height contour) shows a flat indistinct low over the Balkan Peninsula and the Black Sea and a secondary weak minimum over the Baltic States. From the synoptic analysis of surface observations (not shown), one centre of the Balkan Peninsula low lies just within the area of the CF in WA, but over the Baltic States no center can be found. The 500 hPa height contours show a very pronounced upper level trough in the area of the CCB Occlusion. The many parallel contours reaching from Poland to Finland indicate a broad upper level flow from south to north or northeast. The 300 hPa isotach field (Fig. H04B) shows this even clearer; a moderate jet stretching from the western Black Sea over Finland then all the way up to the Barents Sea. Image H05 shows that the cloud bands extending from Romania to Finland are located within frontal conditions. A distinct zone of high thickness gradient from the Balkan Peninsula (CF in WA) extends northward to Finland. The thermal front parameter TFP is located very close to the warm side of this zone - especially on the leading edge of the Baroclinic Boundary cloudiness - but is located more to the rear in the region of the CF in WA. The absence of TFP curvature and TFP around the CCB Occlusion indicates the Occlusion to be a leftover of a previous frontal system and to have only a minor relationship to the frontal band in this study. The maximum of warm advection lies over Poland and White Russia. Only one synoptically important positive vorticity advection (PVA) maximum is located in the south-eastern part of the CF. But noteworthy are the TFP values and the small PVA - area within the warm airmass over Russia, because they are located just at the location of MCS development the following day.

Vertical Cross Sections

The vertical cross-section line lies perpendicular to the CF in WA with orientation from the cold to the warm side (SW-NE), as shown in image H08.

Isentropes and satellite pixel values

In fig. H09 there is a high gradient of isentropes (~ 310-316K) from 400 hPa at 44N/14E down to the surface at 46N/24E, which indicates a frontal zone. Very unstable air is situated immediately ahead of the frontal zone from the surface up to 650 hPa. The cloudiness is represented by a broad peak of grey shades (45N/22E - 46N/26E) in front of the frontal zone and in the unstable area. Some rainshowers were reported along the front.

Temperature advection

WA can be found within and ahead of the frontal zone but only up to 650 hPa. Upper-air cold advection is overrunning the frontal zone, which clearly increases the instability. This is the more unusual type of CF in WA, because usually the WA is situated above the CA which weakens the front, however, in this case, the front is intensifying. In Fig. H12 a zone of convergence is associated with the frontal zone. This is very typical for well developed fronts and contributes to the frontal circulation. Intensive upward motion is located ahead and on top of the frontal zone coincident with frontal and pre-frontal cloudiness. This is a typical configuration of a frontal circulation cell. Convergence within the frontal surface results in upward motion immediately above. The structure of the isentropes in the frontal area would suggest a Kata type Cold Front.