Status:Ongoing analysis Material from: Linus, Fernando
1. Impact
Report from Zoltan Sipos:
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On 17 September, 2017 in northern Serbia and western Romania occurred a derecho event, which corresponds to the definition of this phenomenon: wind damage extends for more than 400 kilometers, includes wind gusts of 93 km/h along most of its length, and also includes several, well-separated 121 km/h or greater gusts. In western Romania, at meteorological or airport weather stations, the wind gusts reached: 25 m/s Sinnicolau Mare, Batos, Sighetu Marmatiei, Bistrita; 26 m/s Zalau, Baia Mare, Ocna Sugatag, Sebes, Alba Iulia; 27 m/s Cluj Napoca, Deva, Toplita, Tg. Lapus, Arad airport; 28 m/s Tebea, Poiana Stampei, Sarmasu, 29 m/s Borod, Holod; 30 m/s Timisoara, Resita; 31 m/s Siria; 32 m/s Varadia de Mures, Rosia Montana; 34 m/s Jimbolia, Gurahont; 35 m/s Stei; 36 m/s Ceahlau Toaca; 39 m/s Banloc, 40 m/s Huedin; 42 m/s Vladeasa 1800. There were 8 dead and dozens injured.
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2. Description of the event
The surface analysis maps from the Met Office shows the development of a surface cyclone from a frontal region south of Alps heading to Ukraine (NE wards) in the next 24 hours. This system was driven by a broad trough in the upper levels evolving into a large cut-off low. So warm air in the south and cold air behind triggered convection along the cold front producing strong wind gusts (~100 km/h). A look at the time series of temperature at some stations we note a sharp drop around 10C just in a couple of hours, indicating the change of air mass.
3. Predictability
3.1 Data assimilation
3.2 HRES
The plots below show 24-hour maximum wind gusts on 17 September from observations (first plot) and HRES forecasts starting from the latest before the event.
3.3 ENS
The plots below show the EFI and SOT for wind gusts valid 17 September.
3.4 Monthly forecasts
3.5 Comparison with other centres
4. Experience from general performance/other cases