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Discussed in the following Daily reports: http://intra.ecmwf.int/daily/d/dreport/2014/09/30/sc/
Picture
1. Impact
Heavy convective showers affected the area around the French city of Montpellier where around 200 mm of rain were reported causing flash floods in the regionOn the 29 September south-western France was hit but heavy rainfall causing flash-floods. Montpellier got around 300 mm and the city was flooded.
2. Description of the event
Warnings on Meteoalarm on the morning of 30 September.
The plot above shows the observed precipitation between 29 September 00UTC and 30 September 00UTC. The worst affected areas were along the coast in the south-west corner of the northern Mediterranean.
Gallery includeLabel precip_an sort comment title Precipitation and MSLP (12-hour forecasts)
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Gallery includeLabel hres_precip sort comment title HRES 24-hour precipitation
The plots above shows the 24-hour precipitation. The hourglass symbol mark Montpellier that got 297 mm.
3.3 ENS
The plot above includes the CDF from the ensemble for Montpellier. The last forecast (29 Sept. 00UTC) had a 4-6% probability for more than 100 mm during the day.
Probabilities of >100 mm/24 hours
Gallery includeLabel ec_prob_100 sort comment title Prob >100 mm/24 ECMWF
The plots above shows the probabilities from ECMWF ENS from different initial times. The strongest signal for heavy rain is located north-west of Montpellier.
COSMO-LEPSGallery includeLabel cosmo_prob_100 sort comment title Prob >100 mm/24h COSMO-LEPS
The plots above shows the probabilities from COSMO-LEPS (16 ensemble members, 10 km resolution) from different initial times. The probabilities are not improved by the higher resolution in this case.
Gallery includeLabel efi sort comment title EFI precipitation
The plots above show EFI for precipitation valid the 29 September for different lead times. Also the medium-range forecast had increased EFI for the area.
3.4 Monthly forecasts
3.5 Comparison with other centres
3.6 EFAS
The plots above shows warnings for flash floods from EFAS from the 28 September 00UTC (left) and 29 September (right). The flash flood forecast is based on COSMO-LEPS. None of the simulations forecast flash floods in southern France but in Spain.
4. Experience from general performance/other cases
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5. Good and bad aspects of the forecasts for the event
- Signal for heavy precipitation in the medium-range
- Under-estimation of the amplitude
- Shift in the maximum from the coast to the mountains in the forecast?
- No signal in EFAS