Low pressure system CHRISSY
(baptized on the 23rd of May 2016)
On the 23rd of May, the synoptic situation over Europe showed a strong ridge with its axis from Greece to Sweden. A ridge is a structure in the synoptic chart, which indicates relatively warm air that has been advected northwards in the lower to middle troposphere, in approximately 5.5 km height. On the contrary, quite a deep trough with cold, polar air was present over Western Europe. At ground level, these two air masses were separated by a frontal system, reaching from Sardinia in the Mediterranean over to Germany and then over to Scandinavia. Forecasting models predicted the development of a new low-pressure system along this front under the influence of the deepening trough. In advance, this cyclone was named CHRISSY by the meteorologists of the Berliner Wetterkarte. Over the rest of the day a closed low-pressure area formed in the middle troposphere as the trough deepened further. This upper-level low moved eastwards over Italy and supported the cyclogenesis of low CHRISSY.
Until 1 am CET of the 24th of May, the depression CHRISSY had formed a first centre at ground level over Croatia. The lowest pressure was around 1007 hPa but the low was still connected to other weak centres, especially along the frontal system that had moved over to Italy, Western Germany and Sweden. Over Southeastern Europe warm, moist, and unstable air offered ideal preconditions for deep moist convection, commonly known as thunderstorms. Another necessary ingredient for storms was given by low CHRISSY due to the fact that cyclones are mainly connected with rising air. Therefore lifted air over Eastern Europe could build clouds, which developed into thunderstorms by converting the energy in the atmosphere into buoyancy. From 7 am to 7 pm CET, the meteorological station in Rimnicu Sarat close to Bucharest measured 48 l/m² precipitation. During the same interval Prague got 20 l/m², Budapest 16 l/m² and Bratislava 14 l/m². Also, the European Severe Weather Database verified reports of hail with diameters over 5 cm, strong winds and even some weak tornadoes. Furthermore, cyclone CHRISSY moved eastwards over Serbia and Romania and intensified quite fast under the influence of the upper-level trough. With the stronger pressure gradient the circulation around the centre intensified as well. Therefore low CRISSY started to deform the frontal system into a cold front and a warm front.
In the early morning of the 25th of May, the centre of the cyclone CHRISSY had increased to under 1000 hPa and had moved over Romania. The cold front was partially occluded at the centre and over to parts of the Black Sea, which means that the front had the characteristics of a cold and a warm front. From Western Turkey, over Crete and the central Mediterranean the front moved as a cold front at upper and lower levels. The warm front reached from the centre over Hungary, Austria and Western Germany up to Denmark, where it passed into another weak low-pressure system. While thunderstorms were still building in the unstable airmass, also the frontal activity created necessary lift for cloud formation and rain. Especially in Romania around the low-pressure centre CHRISSY, large amounts of precipitation were measured again. For instance, the weather station in Targu Ocna measured 34 l/m² and Rozdilna in the Ukraine got 30 l/m² in 12 hours until 7 pm CET. In other cities, such as Graz in Austria, Passau in Bavaria or Ankara in Turkey, weaker showers brought 1 l/m², 0.2 l/m² and 0.6 l/m² during the same time interval. In addition, strong wind gusts were recorded with up to 80 km/h around Vienna.
Due to the cyclonic or counter-clockwise rotation around the low CHRISSY a spiral cloud band had developed by 1 am CET of the 26th of May. The central pressure on the other hand had decreased to around 1003 hPa. Still an occlusion was analysed from the centre CHRISSY over the western Black Sea to the east and then curving south over Turkey where it changed into a cold front over the Mediterranean, Egypt and then reached west along the coast line of Libya. The airmass within the low-pressure area CHRISSY was still able to produce some showers and thunderstorms in the region around the western Black Sea on this day. As a result, Melitopol got 24 l/m² precipitation between 7 am and 7 pm CET. In Predeal, 23 l/m² were measured and further south the cities of Adapazari and Konya got 12 l/m².
Over the 27th of May 2016, the low-pressure system CHRISSY began to dissolve. The central pressure had increased to around 1010 hPa. However, the occlusion, which was once more analysed mainly over the Ukraine, produced some more showers with up to 26 l/m² in 12 hours in Kobeliaky, 12 l/m² in Kiev, 13 l/m² in Serbka and also 12 l/m² in Chopok. Until 1 am CET of the following day, cyclone CHRISSY had vanished from the synoptic chart of the Berliner Wetterkarte.
Geschrieben am 26.07.2016 von Jannick Fischer
Berliner Wetterkarte: 25.05.2016
Pate: Chrissy Ingram