Status:Ongoing analysis Material from: Linus Mohamed, Florian, Ivan
Discussed in the following Daily reports:
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http://intra.ecmwf.int/daily/d/dreport/2014/05/16/sc/
http://intra.ecmwf.int/daily/d/dreport/2014/05/19/sc/
1. Impact
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Between13-16 May 2014, severe rainfall hit south-eastern Europe. The worst affected countries were Serbia and Bosnia - Herzegovina where the rain is said to be the worst for 120 years. Currently more than 35 people have died in land-slides and the flooding following the rain. Heavy rainfall and strong winds also affected Austria, Slovakia and other neighbouring countries. |
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2. Description of the event
The severe event started on 13th May with rain along a cold front and strong westerlies. From 13th throughout 14th May an upper-level low formed together with a deep surface low tracking through Bulgaria. Then the heaviest rain fell in parts of Serbia and Bosnia. At the same time severe thunderstorms developed over Bulgaria and Romania bringing hail and strong winds. A tornado or tornado-like phenomena were reported in western and northern Bulgaria damaging severely some houses. The following day the deep surface low was slowly moving to the NW bringing further heavy rain over Serbia. The upper-level cyclone also moved slightly to the NE. On 16th the the low pressure system staying over the Balkans started dissipating. In its northern fringes heavy rain was reported in Slovakia and Austria. On the 18th May in the northern fringes rainfall continued over Austria, Poland and Slovakia with heavy showers as previous days over the rest of the area within the cyclonic circulation.
The figures below show the analyses of t850 and z500 (00UTC). The rainfall was caused by a cut-off low situated over south-east Europe, bringing moist winds from east, hitting the mountains on Balkan.
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The figures above show the observed precipitation for the 14,15, 16 and 17 May (06-06) and the HRES forecast (day 2-3). The forecast underestimated the precipitation in the worst affected areas.
The figure below shows the 5-day accumulation (13-18 May 00UTC). For 5-day accumulations unfortunately no station appears over Serbia but I found some stations in Austria, Slovakia, Poland and Romania where 5-day totals exceeded 99th percentiles of the 15-year observed climate. On the plot below you can see two examples.
The table below shows the observed precipitation for Loznica (13262, 44.3N, 19.1N), Beograd (13274, 44.9N, 20.3E) and Valjevo (13269, 44.2N, 19.5E). The precipitation is the 24-hour observed at 06UTC. The total for the 5-day period (12 May - 17 May 00UTC) was for Loznica 219 mm, Beograd 190 mm and Valjevo 199 mm.
| Loznica | Beograd | Valjevo | |
|---|---|---|---|
| 13 May | 0 | 0 | 6 |
| 14 May | 50 | 21 | 38 |
| 15 May | 110 | 108 | 108 |
| 16 May | 53 | 45 | 44 |
| 17 May | 6 | 16 | 3 |
| 18 May | 0 | 0 | 3 |
The connection to the system giving all the rain, high wind gusts where measured, especially in the Slovakian mountains with wind gusts of more than 40 m/s.
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The figure above shows the 3-day accumulated precipitation in the box 44N-45N, 18E-20E from different initial dates (from different resolutions). In the deterministic forecasts a hint of the extreme rainfall started to appear on 6 May. The T319 forecast was very consistent from 6 May 12UTC (probably with a large portion of change).
3.3 ENS
On 14th May in Serbia and Bosnia heavy rain between 40 and 130 mm just in 24h was recorded. From the few stations in Serbia displayed on the plot below we can see that 24-hour accumulations exceeded the 99th percentile of the observed 15-year climate. The most extreme precipitation was observed in Loznica, a station in western Serbia at the border with Bosnia where 129 mm were recorded on 14th May whilst the climate maximum is just 68.4 mm. Comparing the forecast with observations we can notice that 7-days in advance the tail of the forecast consistently predicted extreme values of the rainfall but the forecast was uncertain and therefore EFI values were positive but not high whilst SOT was positive indicating a possibility of an extreme event. Approaching the day of interest forecast CDFs became more extreme ending up with really extreme CDF in the most recent forecast on the day of the extreme rainfall. We can also notice that the forecast underestimated the rainfall totals even for the most extreme members but at the same time such an extreme rain as observed in Loznica seem locakized. All the other stations around measured rainfall amounts between 40 mm and just above 100 mm which is close to the rainfall in the most extreme ensemble members.
Gallery includeLabel efi_d5 sort comment title EFI 5-day (12-17 May)
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