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The plot above shows comparison of three consecutive short-range HRES forecasts versus the observed 24-hour rainfall (top left panel). Observations are displayed with numbers while the shading represents a combination of LAM ALADIN and observations to create precipitation analysis on a regular grid. The analysis data are kindly provided by the Forecast Department of the National Institute of Meteorology and Hydrology in Bulgaria. It shows huge amounts of rain over NE Bulgaria. Rainfall totals of 155 mm were recorded in two stations and few other with rain above 100 mm. Although this is a 24-h accumulation it actually fell in just in few hours. The convective nature of the rainfall makes forecasting of this event very difficult. Indeed, the short-range HRES forecast gives considerable amounts of rain but not surprisingly the largest totals are misplaced. What is a little bit surprising is the fact that the latest forecast seems worse than previous two over NE Bulgaria where the largest amounts were recorded.
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The flash floods occurred on 19 June in the evening and in early morning on the 20 June when just in few hours more than 100 mm of rainfall were recorded in NE part of the country. Flash floods occurred there. The analyses show that 99th model climate percentile for 24h total rainfall was exceeded in many places in the east of Bulgaria. Some local heavy showers were observed in some far western regions of the country as well. If we compare observations with the 95th model climate (M-climate) percentile, we'll notice areas of local torrential downpours in many parts of Northern Bulgaria as well. The shortest range EFI forecast matches quite well the areas affected by heavy rain but the EFI has never reached extremely high values close to 1 over NE Bulgaria. This could be is more likely due to the convective nature of the rain and the large uncertainty in the forecast that we might expect in such cases. Note that there is 6-hour shift between the validity of the EFI forecast and the accumulations represented by the observations: EFI is valid from 00 to 00UTC whilst accumulations are for periods of different length starting from 06UTC.
Observed 24-hour total precipitation compared with the model climate. Red triangles denote accumulations that exceed certain model climate percentiles (95th or 99th percentile). Green triangles on the EFI forecast plot denote observations that exceed 99th model climate percentile. The shortest range EFI/SOT forecast is also displayed. The CDFs from the most affected regions show that the forecast was quite uncertain and precipitation amounts were underestimated although they appear extreme compared to the M-climate.
The EFI forecast provided good guidance throughout the forecast from longer the longest to shorter lead times. At the beginning, 7 days in advance, positive SOT over Bulgaria showed a risk of abnormal rainfall whilst the EFI was positive but still values were low. Closer to the event the EFI became higher.
EFI forecasts for 24-hour total precipitation with observations on top. Green triangles denote observations that exceeded 99th model climate percentile.
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Observed 72- and 120-hour precipitation compared with the model climate. Red triangles denote accumulations that exceed certain model climate percentiles (95th or 99th percentile). Green triangles on the EFI forecast plots denote observations that exceed 99th model climate percentile. The shortest range EFI/SOT forecast is also displayed.
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