Status:Ongoing analysis 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.
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
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