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 Status: Finalised Material from: Linus, Tim


1. Impact

On 29-30 April a cyclone formed over France and moved northwards. In front on the cyclone severe convection appeared with reported tornado over Belgium. The cyclone itself led to heavy rain along the French, Belgium and the Netherlands. However, 1-3 days before the main part of the rain was predicted to fall over southern England.

2. Description of the event

The plot below shows the surface analysis from Metoffice on 30 April 06UTC.

The plots below show satellite images (Meteosat channel 9) from 29 April 18UTC to 30 April 18UTC every 6th hour.

The plots below show z500 (contour) and t850 (shade) analyses from 30 April 12UTC to 1 May 00UTC every 12th hour.

The plot below shows the 24-hour maximum wind gusts during 29 April. One station in Belgium reported more than 40 m/s.

Severe weather reports and ATDnet lightning density on 29 April 2018. Two tornadoes have been reported - one in NE France and another one over SE Belgium.

3. Predictability


3.1 Data assimilation

The plots below show surface Obs with alarms triggered for 30th April (left), example of obstats for one such ob in the middle of the cluster (middle) and MSLP for 06Z from background (blue) and LWDA analysis (red (right).

3.2 HRES

The plots below shows 24-hour precipitation (30 April 06UTC to 1 May 06UTC) from observations (first plot) and HRES forecasts.

3.3 ENS

The plots below shows EFI and SOT for CAPE/SHEAR in 1-day forecasts valid for 29 April (left) and 30 April (right).

The plots below show EFI and SOT for total precipitation on 30 April.

The plots below show cyclone feature plots valid 30 April 12UTC. The colour of the dot represents the maximum precipitation inside a 300 km circle.

The plots below shows the evolution for 24-hour precipitation on 30 April for Rotterdam (left) and Reading (right) for ensemble (blue) and HRES (red dot). Then the western edge shifted in the last forecasts before the event, Reading became on the dry side while the rain appeared further to the east (e.g Rotterdam) instead.

Convective hazards forecasts valid for 29 April picked up severe convection 4 to 5 days in advance.

3.4 Monthly forecasts

3.5 Comparison with other centres

4. Experience from general performance/other cases

5. Good and bad aspects of the forecasts for the event

6. Additional material