Status:Ongoing analysis Material from: Linus, Gianpaolo
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Discussed in the following Daily reports: |
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2. Description of the event
Five days of rain in the North-West of Italy: this was well forecasted since November 19 when most of the NWP models consistently predicted an extended rain event between Monday 21 and Friday 25 November. Sirocco wind from south associated with a cutoff low on the western Mediterranean, brought mild and humid air, and the orographic enhancement of precipitation due to the Apennines of Western Liguria and the nearby Alps surrounding the Piedmont region made the rest to amplify rainfall quantities to exceptional amounts. The rainfall data collected from the insitu monitoring stations operated by ARPA Piemonte show the largest amount of rain has fallen on mountainous areas of the Piedmont region during the week and then the water was released to downstream generating floods in the Po valley: focusing on the 48 hours between 15:30 on 23 November to 15:30 on 25 November (local time), the most severe case have been registered with quantities that easily and widely exceeded 250-300 millimetres of rain (top left panel). If we consider Monday-to-Friday, Cuneo area in five days got 686 mm of rain in Piaggia, of which 295.8 mm fell in one day on Thursday 24 November (chart above right) and 650.4 mm of rainfall in Ponte di Nava Tanaro, of which 343 mm fell in one day on Thursday 24 (chart bottom right). Also in Cuneo, considerable accumulations in Barge (573 mm, 375.6 mm of which fell on Thursday 24), Limone Pancani (566.6 mm, 216.8 mm of which fell on Monday 21) and Borello (506.8 mm, 246.4 mm of which fell on Thursday 24). The flood is comparable to November 1994 and even larger amounts of rain have occurred. However while in 1994 the human loss counted 70 casualties, only 1 person lost his life in this event.
Data source: ARPA Piemonte.
The sequence below show 12-hour precipitation forecasts and MSLP ranging from 18-25 November. The worst rainfall events were on 21-22 November and 24 November.
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