201605 - Convection - Europe

 Status:Finalised Material from: Ivan, Ervin, Linus

Discussed in the following Daily reports: 

1. Impact

 During the last days of May, western and central parts of Europe from France to Poland and Hungary was hit by events of severe convection and heavy rainfall. A man was killed in southern Poland hit by lightning. In Paris, a birthday party in Parc Monceau was struck, injuring 11 people, eight of them children on Saturday afternoon, 28 May. Several are in a life-threatening condition. Three people were seriously hurt at a youth football match in Germany. Heavy rain caused some localized flooding as well. On 29 May to 30 May torrential rain hit south-western Germany and killed four people. Flash floods affected many businesses and homes. The worst affected region is the town of Braunsbach where floodwaters swept away two bridges as well. Dozens of homes there are at risk of collapse and must be evacuated. This investigation will focus on the event in Germany.

2. Description of the event

The synoptic circulation was quite stationary and characterised with omega pattern over Europe: lows over the Atlantic and the Black Sea area and highs over the Mediterranean and northern parts of the continent. The areas affected by severe convection were located over a strong SW to W flow in mid troposphere and weak winds near the surface. Air mass was unstable with substantial deep layer shear which favoured the formation of supercells and organised convective storms.

A nice animation of satellite images from EUMETSAT can be found here:

Severe weather reports from the European Severe Weather Database (ESWD) maintained by the European Severe Storm Laboratory (ESSL) are plotted below for the last few days of May.

3. Predictability

3.1 Data assimilation

As we recently have started to assimilate humidity observations from a few Lufthansa aircraft, this is a good case to monitor the use of this data.The plot below shows the the observation statistics for humidity observations from aircrafts for the lower part of the troposphere. The box is centred on Frankfurt to get observations from ascending and descending flights.

3.2 HRES

HRES forecasts and observations from precipitation valid 29 May 06z- 30 May 06z. The last forecast (29 May 00z) captured the region of maximum precipitation.

3.3 ENS

The plots below show EFI an SOT for total precipitation valid 29 May. All lead times up to 6 days before the event showed increased risk for extreme precipitation.

The plots below show EFI an SOT for CAPE and CAPESHEAR valid 29 May.

3.4 Monthly forecasts

3.5 Comparison with other centres

The plots below focus on the 24-hour precipitation for short forecasts for Germany 29 May 06z to 30 May 06z. The plots are for observations, ECMWF HRES, ECMWF ENS (first 20 members), COSMO-DWD (2km) and COSMO-LEPS (7 km).

3.6 EFAS

The plots below show the ERIC flash flood product from 28 May 12z, 29 May 00z and 29 May 12z. The strong indications of flash floods only came in the vary last forecast before the event (the product is based on COSMO)

4. Experience from general performance/other cases

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

• Early (6 days) signal in EFI
• Good short forecast.

6. Additional material