Severe hailstorm in Sofia, Bulgaria

By Georgi Tsekov (National Institute of Meteorology and Hydrology, Bulgaria)

Download Met-10 composite animation, 12:15–15:00 UTC, (upper left IR10.8, upper right HRV, lower left IR3.9, lower right convection RGB)

July 2014 was extremely wet and rainy month in Bulgaria. Monthly rainfall totals in most of the country's synoptic and climatic stations were between 90% and 300% of the norm. There were 28 days with thunderstorms, 20 of which also had hailstorms.

On 8 July at 14:00 UTC (17:00 local time) a severe convective hailstorm hit Sofia, the capital of Bulgaria, with large hailstones.

The local synoptic station recorded rainfall of 23 mm for about an hour and wind gusts of 126km/h.

This weather radar image from 14:09 UTC (Credit: Agency hail suppression, Bulgaria), clearly shows the heavy precipitation over Sofia.

The hailstorm caused a lot of damage to properties and the environment. One person was reported to have died and more than 40 people injured.

It formed as a fast developing convective multi–cell squall system, due to an instable air mass. The instability was caused by warm soil moisture and the approaching cyclone from Central Europe moving towards the north-west parts of Balkan Peninsula and its related frontal systems.

The 2m temperature immediately before the storm was almost 30°C.

That morning in Sofia, just before the storm, the atmospheric pressure was around the monthly average and until the storm it decreased by 4hPa for six hours.

Vertical profile (Figure 2) generated by information from the radiosonde launched near two hours before the storm, showed high instability values (Lifted Index, K-Index, CAPE and etc.) and big quantity of precipitable water.

The formation of the convective cell started at 10:30 UTC in far eastern parts of Serbia. It grew and moved eastwards, than split on two main storms: one moved to east-south-eastwards (directly to Sofia), the other one to the north-east (through the Balkan Mountains to Danube's river plate).

The peak of the first one was over Sofia between 13:50 UTC and 14:30 UTC, after that it began to dissipate.

There was also third, independent storm at the same time, in the southern part of the country.

EUMETSAT's MSG-SEVIRI images and the products made of them, well describe the microphysics and kinetics of the process.

The yellow colour on the Convection RGB (Figure 4) gives information about the presence of small ice particles in the cloud and strong updrafts. The IR10.8 brightness temperature image (Figure 3) help us to recognise the storm as cold ring-shaped.

It's important to say that in the day before the storm the output data forecast of the main numerical models didn't highlight a possibility for heavy rains in that region.

The MPEF GII Lifted Index product (Figure 5) shows the instability in this region six hours before the storm.

Additional content

Hailstorm in Sofia, Bulgaria 8th July 2014 (YouTube)
Over 40 People Injured in Heaviest Hailstorm to Hit Sofia (Sofia News Agency)
Damage Claims After Heavy Hailstorm in Sofia Worth Over BGN 100M (Sofia News Agency)