The locations of surface trough and upper trough indicate a configuration for a developing low with trough axis tilting backwards.

All numerical key parameters for wave development (positive vorticity advection at 500 hPa as well as warm advection) are fulfilled quite well around the Lofoten Islands.

The PVA distribution at 500 hPa shows two distinct maxima. The first one is associated with the Icelandic upper level trough, while the other is connected to the upper trough and developing Wave over the Lofoten Islands. The inspection of vorticity components, shear and curvature shows that the resulting PVA is due to both vorticity and curvature vorticity north-west of the Lofoten Islands. The model indicates one distinct very broad jet streak from the north-west across Scandinavia to north Germany and Poland. However, inspection of the WV image reveals two Dark Stripes, indicating two separate jet axes. The western one extends from the north-west to west Sweden and is associated with the south-western cloud band. The second stripe extends from the north-west to west Finland. However, the model jet axis is in the middle between the two Black Stripes in the WV image. It seems quite clear that the ECMWF model does not resolve the two jet axes satisfactorily, even though the model vaguely indicates a double structure with two separate jet maxima over south and north Sweden. The actual soundings around the Bay of Bothnia at 06.00 UTC (not shown) actually indicated that the jet stream and, accordingly, the shear on the cyclonic side of the jet were more intensive than the model suggested.