Model Error
On September 12th at 12UTC, a black zone illustrating dry stratospheric air with a high PV (Potential Vorticity) extended from France to the Benelux countries. Convection, which can be seen as distinct white spots in the WV-images, was initiated on the eastern flank.
The ECMWF model output (00UTC run) also detected this black zone, but shifted it significantly westwards, especially over France (Fig 2.7). That is to say, that the model had a clear lag and the convection cells with rain showers and isolated thunderstorms reached Austria a little bit earlier. At night the first convective cells occurred in Vorarlberg and Tyrol.
The 00Z model output, however, was better and adjusted for the shift. Also, the splitting of the PV anomaly was well computed (Fig 2.8).
A reason for this shift may be that the PV anomaly had developed over the Atlantic Ocean and moved quickly towards Europe. The scarcity of data from the Atlantic could have caused the error. For the next model run more data was available and so the shift was corrected.
Figure 2.7: Meteosat 9 WV6.2 and PV315K model field (00UTC run) - 12 September 2010 12UTC
Figure 2.8: Meteosat 9 WV6.2 and PV315K model field (12UTC run) - 13 September 2010 00UTC