Status: Finalised Material from: Ivan, Linus, Tim, Andrea
1. Impact
On 21 October severe rainfall hit north-western Italy, both in the Alps and in the mountains close to the coast north of Genua.
2. Description of the event
The plots below show analyses of MSLP and 6-hour precipitation forecasts every 12h hour between 19 and 22 October.
The plots below show the analyses of z500 (contours) and t850 (shade) from 18 to 22 October.
The event north of Genua was clearly a convective event, and convection initiated over the mountain to the north of Genoa and kept developing over an incredibly long time as seen in the satellite animation below.
The gradient of precipitation was massive with observations of 451 mm/24h and 13 mm/24h only 11 km away from each other.
3. Predictability
3.1 Data assimilation
3.2 HRES
The plots below show observations and forecasts of 24-hour precipitation valid from 21 October 06UTC to 22 October 06UTC. With the northern maximum (in the Alps) was well captured, also the shortest HRES forecast missed the southern maximum ( close to Gulf of Genua). The precipitation maximum in the forecast was rather over sea.
The maximum observed 24-hour precipitation in the outlined box [45.25N, 8.5E, 44.25N, 9.5E] was 502 mm, while the latest forecast (21 Oct 00UTC) had 105 mm. The mean of the 118 observations was 69.6 mm and the forecast mean for the same points 39.9 mm. The area average in the forecast was 29.2 mm.
Obs in box:118 69.6
Fc for obs in box:118 39.9
Fc int/max in box:29.2 105
3.3 ENS
The plots below show EFI and SOT for total precipitation valid 20 October.
The plot below shows the evolution of forecast for 1-day precipitation valid 21 October 06UTC to 22 October 06UTC for the 1x1 degree box outlined in the HRES plots above. The plot includes ensemble (blue box-and-whisker), HRES (red dot) and model climate (red box-and-whisker). The average for the observations in the same box was 70 mm, but for the same locations the second last HRES (red dot) had an average of 40 mm, compared to 30 mm as the box average. Anyway the mean precipitation was clearly underestimated by the shortest forecasts.
3.4 Monthly forecasts
3.5 Comparison with other centres
As for the performance of limited-area systems, COSMO-2I (operational Italian version of COSMO run at 2.2 km of horizontal resolution) provides a good short-range forecast of the event. In the map, you can see the 12-h precipitation cumulated between fc+12h and fc+24h for the run stating at 00UTC of 20191021. Precipitation maxima are between 200 and 300 mm.
4. Experience from general performance/other cases
- Similar structure as 201509 - Rainfall - Southern Europe
5. Good and bad aspects of the forecasts for the event
- ECMWF forecasts clearly missed the extreme north of Genua
- Better prediction of the extreme in the Alps
1 Comment
Alessio Canessa
In favor of ECMWF: on day 20 HRES forecast high precipitation for 21 on the Gulf of Genoa, this led Liguria Region and the Italian Air Force Met Service to issue a red alert for Liguria on day 20.COSMO D2 also provides a very good short-range forecast of the event.