Jets (Isotachs) + PVA 300 hPa

The first image shows an intense jet (yellow, wind speed up to 75 m/s) extending from Greenland over Iceland Scotland to North Scandinavia. The area of the instant occlusion was situated in the left exit region of the jet streak over the North Sea. Strong maxima of PVA (red) coincided with the cold front as well as with the cellular cloudiness behind the front.

The jet and the upper air trough moved to the South East. The axis of the jet was located on the rear side of the frontal cloud band. Strong cyclonic curvature was connected to the area of the instant occlusion and contributed to PVA. The comma-like cloud feature behind the front was not clearly imposed by PVA like in an ideal case. However, PVA at 500 hPa gives a much better fit at this time step.

Comma and the frontal cloud band came closer together. The PVA maximum over the North Sea was linked to the left exit region of the jet streak and covered parts of the cold front and the comma.

A strong maximum of PVA is mainly found in the area of the cold front. This PVA maximum is typically east of the PV-anomaly that had just arrived the East coast of England.

The comma and the cloud band have merged completely. The model fields reveal PVA above the frontal clouds.

PVA reached far into the center of the jet streak hinting at the existence of strong curvature vorticity. The jet axis was localised parallel to the rear edge of the cold front. It crossed the cloudiness in the area of the instant occlusion. However, wind speeds were decreasing in this area.

The occlusion spiral was well developed. Wind speeds continued decreasing. Near the vicinity of the cloud spiral only low wind speeds and and only small PVA-values can be seen. It is likely that the cyclone will weaken during the next hours.

The cloud spiral moved slightly to the West. Only negligible PVA near-by can be oberved.

Cloud decay of the occlusion spiral and low PVA values mark the end of the hazardous weather situation.