Cloud streets over the Black Sea

By Mária Putsay, Kornél Kolláth and Ildikó Szenyán (Hungarian Meteorological Service)

Cloud streets are rows of cumulus or cumulus-type clouds aligned parallel to the low-level wind (see conceptual model).

The surface chart on 24 February (00:00 UTC) shows the synoptic situation characterised by an anticyclone over the Eastern European Lowland and a cold front which has just left the Black Sea area. Both, the ECMWF surface wind analysis and the SYNOP observations show the cold air outflow from the very cold and mainly snow-covered Eastern-European Lowland to the warm Black Sea.

The cold air coming from the north picks up humidity and heat from the sea surface, which leads to the onset of convection in the form of cumulus cloud streets. The convective cells get larger and deeper the further the cold air runs over warm, open water due to the continuous heat and humidity input.

The detailed structure of the cloud streets can be well observed in Meteosat-8 HRV images (see 09:00 UTC image and animation) or in RGB composites that make use of this high-resolution channel (see RGB composite NIR1.6, HRV, HRV and animation).

Another interesting phenomenon can be observed in the HRV images, namely low level lee wave clouds south of the Black Sea caused by the mountains in Turkey (see 05:30 UTC image). Note also a large dust cloud that can be seen over the Mediterranean Sea (see 11:45 UTC image) and a cirrus cloud band over Central Europe and the Mediterranean Sea consisting of very small ice particles due to earlier high aerosol input by the dust storm.