On the afternoon of 22 April, a series of severe convective storms developed in the region of Bulgaria, Romania and south-west Ukraine.
06 December 2022
22 April 2008
Two of these storms developed several significant cloud-top features, observed by weather satellites, commonly ranked as indicators of possible storm severity.
These features were: high 3.7/3.9µm cloud top reflectivity, well-developed plume above one of these storms, and namely a cold-U shape feature on top of one of these storms, and a cold-ring shape on top of another storm. It is the successive occurrence of these two latter features which makes this case extremely important for conceptual models of the two features, and of convective storms in general.
The cold-U shape disappeared between 15:15-15:30 UTC, and the storm dissipated shortly after. The second storm (labeled 'B' in Figure 2) formed at about 16:00–16:15 UTC approximately in the same area in Romania, where the storm A had weakened, just behind it. From 16:15 UTC this storm had a well-defined cold-ring feature in its cloud top, which persisted until about 18:00 UTC, when the storm weakened and dissipated above south-west Ukraine.
The importance of this case is in the successive occurrence of the two features (cold-U and cold-ring shapes) in such a close proximity. It is believed that the main difference between the two types of storms is linked to the environmental wind shear. If so, the occurrence of the cold-ring shaped storm B in the track of the first one, the cold-U shaped storm A, can be explained by several ways:
- Modification of the environment by the storm A.
- Formation of the cold-U shape is not only a result of the environment, but also of some processes inside storm A (at the same time forming the distinct plume above the storm) and/or by the 'plume-masking mechanism'.
- Different cloud-top heights reached by the two storms, thus interacting with slightly different environmental winds. The possible mechanisms above will be further studied, together with other satellite and radar characteristics of these two storms.
As regards ground observations, the case was associated with reports of thunderstorms, strong wind gusts, hail and tornadoes. In Bulgaria, several tornadoes were reported in the area of Zavet, Sushevo and Ostrovo (see map from European Severe Weather Database (ESSD ) and a film footage of a tornado taken by Tihomir Velikov (Hydrologist at NIMH-BAS in Razgrad) with his phone.
Furthermore, hail was reported in many places (26 climatological and synoptical stations) in northern Bulgaria, mainly in the area of Razgrad, Targovishte and Roussee. In Romania, the villages and cities affected by the storm (electricity outage, fallen trees, houses and cars damaged, roads blocked) were situated on a path oriented from SW to NE, in the Constanta and Tulcea counties (see red circles on map of Constanta county).
Met-9 Channel 12 (HRV) Animation 11:00–17:15 UTC
Met-9 Channel 04 (IR3.9) Animation 11:00–19:00 UTC
Met-9 WV6.2 - IR10.8 Animation 11:00–19:00 UTC
Met-9 RGB Convection Animation 11:00–19:00 UTC
NOAA-15 AVHRR Channel 02 (VIS0.8) 14:30 UTC
NOAA-15 AVHRR Channel 03b (IR3.7) 14:30 UTC
NOAA-15 AVHRR Channel 04 (IR11.0) 14:30 UTC
NOAA-15 AVHRR RGB VIS0.6, VIS0.8, IR11.0 14:30 UTC
NOAA-15 AVHRR RGB VIS0.6, VIS0.8, IR11.0 blended with IR11.0 image 14:30 UTC
Precipitation map Bulgaria 22 April