Status:Ongoing analysis Material Status: Finalised Material from: Ivan
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Discussed in the following Daily reports:
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In the evening hours – between 18 and 21 UTC (UTC+3h local time) on 6 July 2020 a multi-cellular thunderstorm brought torrential rain and caused flooding in the Bulgaria's capital of Sofia. The heaviest rain was recorded in the western and especially south-western parts of the metropolitan area. High wind gusts also accompanied the thunderstorm.
Rainfall totals in Sofia metropolitan area (yellow numbers). Rainfall data are from a set of automated meteorological stations at the National Institute of Meteorology and Hydrology and from Stringmeteo. Mountains and the highest point in each around Sofia valley are also given as a reference; Sofia valley is between 500 and 600 m of altitude.
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EUMETSAT satellite imagery and ECMWF Z500 analysis at 12 UTC (left) and 18 UTC (right).
Airmass RGB animation.
SkewT-logP diagram of the sounding at 12 UTC from the central meteorological station at the National Institute of Meteorology and Hydrology situated in the eastern part of Sofia metropolitan area.
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There is evidence that the thunderstorm over Sofia became so intense because of the specific vertical wind profile and the compex orography of the area – easterly, north-easterly in the boundary layer directly hitting northern foots of Vitosha mountain, constantly initiating new convective cells and their slow motion to the north, north-west.
3. Predictability
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It is striking that NWP guidance was so poor. Even convection-allowing model AROME at 2.5 km of grid spacing failed to predict any rain in the area. ALADIN at 5 km and ECMWF HRES also has literary 0 rain during the torrential rain.
3-hourly precipitation for 15-18 UTC (top) and 18-21 UTC from ALADIN, AROME and ECMWF HRES.
3.1 Data assimilation
3.2 HRES
ECMWF HRES in the short range shows afternoon showers over the area but the timing was wrong – all the precipitation in the model occurred before 18 UTC; the shift in afternoon convection was more than 3 hours – convection in the model precipitated more than 3 hours earlier. Precipitation amounts in the forecast were considerably underestimated.
3.3 ENS
The post-processed product ecpoint rainfall increased precipitation amounts at the upper tail but even these amounts clearly underestimated the extremity of the event.
99th percentile of 12-hour precipitation from the raw ECMWF ENS (left) and ecpoint rainfall (right).
3.4 Monthly forecasts
3.5 Comparison with other centres
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