Satellite Overview

The distinct Warm Front Band over Finland is accompanied by precipitation (Fig. H59). The MCSs over Eastern Finland are accompanied by thunderstorms. The second part of the Warm Front structure from Poland to Sweden is also producing widespread precipitation. The chaotic cloud structures over the Baltic States have no connection with the Cold Front band structure over the Ukraine. The chaotic clouds could be partly explained by the Warm Conveyor bBelt. The former CCB Occlusion still shows some remnants over Romania.

Parameters on isobaric surfaces

In the WV image (H60), an appearance similar to that of 18.00 and 00.00 UTC can be seen; the broad WV band has moved westward across Sweden to Norway. The separation of tropospheric and stratospheric air at the western edge of the WV band is above 300 hPa. Again there is a displacement between the zero line of shear vorticity and the Dark Stripe in the WV image. Stratospheric air has descended down to 450 hPa in the ULL as well as behind the CF over the Black Sea. The situation is again very similar (H61). The area of the surface low is filled with very unstructured clouds. The Warm Front and Cold Front bands are generally coincident with surface troughs, and with the Swedish part of the Warm Front being better aligned with the upper level stream. This is not a typical development: the clouds of the Baroclinic Boundary and the upper level trough already existed before the surface lows developed. They are more a reformation of cloud structures rather than new developments The Warm Front characteristic is very distinct over the Baltic Sea and Finland, with respect to thickness gradient, TFP and WA maximum (H62). The zero line of temperature advection crosses the centre of the surface low.

Vertical Cross Sections

The vertical cross section is drawn perpendicularly to the Warm Front Band over Finland and to the rest of the Baroclinic Boundary over Norway and crosses the Warm Front from east to west (H63).

Temperature advection

The vertical cross section is drawn perpendicularly to the WF band over Finland and to the rest of the Baroclinic Boundary over Norway and crosses the Warm Front from east to west (H63).

Convergence

The zone of convergence is now more distinctly associated with the Warm Front zone than before; convergence within, divergence below and above (H65).

Vertical motion

A well developed circulation cell with convergence seen within the frontal zone, and with upward motion above it (H66); air is sinking below the frontal zone. There is very distinct agreement between upward motion and highest satellite pixel values.

Frontogenetic forcing

High values of frontogenesis are associated with the frontal zone (H67).

With help of parameters on isentropic surfaces: Air mass separation

Very typical distribution of humidity can be found: humid zone above the frontal zone, very dry zone below the frontal zone (H68). Selection of characteristic isentropic surfaces (Fig. H54):

• 310K: mainly within the frontal zone but more in the lower part;
• 324K lies above the frontal and unstable zones.

Downward inclined isentropes (400 to 900 hPa) are dominant in the lower part of the frontal zone, which can be interpreted as sinking dry air (H69). At a higher isentropic level (Fig. H70) the rising relative streams (w.c.b) can be found over the Baltic Sea and S. Finland, while the relative streams are more or less parallel to isobars or only slightly sinking in the northern part. To the rear of the Cold Front, and within the former CCB Occlusion, there exists a completely different relative stream, which shows that the separation of the relative streams between these two systems is now much more distinct than 6 hours earlier. The PV field (H71) is similar to that 6 hours earlier. A distinct gradient between tropospheric and stratospheric air can be found at the western boundary of the WV band at a height of 300 hPa. In the troposphere, stratospheric air has penetrated downward behind the Cold Front over the Black Sea. The Warm Conveyor Belt transports warm moist tropospheric air upward, while the relative stream in the SE part of the image transports dry stratospheric air (H72).