Life story

 

Low pressure system PIERRE

(baptized on the 10th of February 2017)

 

On the 10th of February a low pressure area northwestern of the Iberian Peninsula was named PIERRE by the meteorologists of the Berliner Wetterkarte, after this atmospheric depression was moving eastwards over the Atlantic Ocean towards Central Europe. On this date the air pressure in the center was set at 990 hPa. At an advanced state of development the depression PIERRE showed an occlusion front that extended northwards crossing Iceland and eastern parts of Greenland. Occlusion fronts occur when the faster moving cold front overtakes the corresponding warm front of a system which is ahead.

Embedded in a trough of low pressure in a height of 5.5 km, that was reaching to northern Africa, the depression PIERRE had an air pressure of 1000 hPa on the 11th of February. Its occlusion front was proceeding to Spitsbergen over the Atlantic Ocean in a lightweight bow.

On the following day, the active depression PIERRE moved to the south coast of Portugal with an air pressure below 995 hPa in its center. From this location the occlusion front continued moving over Morocco and finally ended over the Atlantic, roughly on the same latitude as Madrid. Regions located in the zone of cyclone influence recorded precipitation quantities of 19 l/m in Agadir, 32 l/m in Ourzazate, 16 l/m in Gibraltar, 21 l/m in Beja or 17 l/m in Seville measured in 24 hours until the evening. Especially the north of Spain measured maximum gusts of up to 140 km/h in Cerezo de Arriba or 115 km/h in Nestares, which are storm forces 12 and 11 on the Beaufort wind scale.

By moving northeastwards, the cyclone with a center air pressure of 995 hPa was located at the northern end of Portugal on the next day. Around the center of the depression PIERRE the occluded front of the system extended until it reached the triple point, where the warm front crossed Spain. To the west of the warm front the cold front of the system extended from Spain to Morocco. On the 13th of February, the cyclone PIERRE mostly influenced Portugal and Spain. Uplifting of air masses and clouding led to precipitation around the frontal system. While most parts of the influenced area only measured low precipitation rates, some meteorological stations reported 2 l/m like Lisbon, 5 l/m like Ponferrada or 7 l/m like the city Gibraltar.

Situated slightly western from Ireland, the low pressure area PIERRE reached an air pressure of unchanged 1000 hPa on the 14th of February. Its cold front continued reaching over the Bay of Biscay, the South of France, parts of the Mediterranean Sea and finally ended over Algeria. The warm front of the system advanced over the North Atlantic to the south of Iceland. Considerable amounts of precipitation were falling in Portugal and in the south of France. The active trough was leading to heavy rainfall with amounts of 51 l/m in La Molina, 46 l/m in Port Vendres, 34 l/m in Fisterra or 59 l/m in 24 hours at the station on Mont Aigoual, which is at a height of 1567 m. A temperature drop in higher atmospheric layers made the precipitation in mountainous regions fall as snow rather than rain.

On the next day the cyclone PIERRE, now lying western from the British Isles, was showing a complex frontal system. While one cold front was moving to the north of Portugal and connecting to a warm front that was leading to an unnamed cyclone over the Atlantic, the occluded front dispersed to the north, splitting up into a cold front that passed Great Britain and changed into an occlusion that moved further to France. Also another warm front was reaching Iceland. After bringing continuous heavy rainfall to the Iberian Peninsula, the cyclone PIERRE caused precipitation amounts of only 11 l/m in Church Lawford in England, 5 l/m in Benson or 4 l/m in the Irish city Gurteen. On the one hand, the depression PIERRE was shifting northwards with weakening. On the other hand, the low pressure trough the cyclone was embedded in was intensified and moved to Central Europe.

As the cyclone PIERRE further developed, it was forming two low pressure centers. One was situated northwestern of Scotland and named PIERRE I and the other cyclone center PIERRE II was analyzed between Iceland and Scandinavia over the sea. The frontal system of the center PIERRE I was influencing the British Isles and France, the weather in Scandinavia was determined by the center PIERRE II. Along the Norwegian coast, precipitation amounts reached 17 l/m in Hammerfest, 11 l/m in Alfjord, 12 l/m in Bergen and 7 l/m in Landvik. Stornoway measured 12 l/m and winds of force 8. Aonach Mr even reported maximum gusts of 115 km/h and the meteorological station on the Cairngorm Mountains even 122 km/h. The corresponding low pressure trough in 500 hPa above Western and Central Europe, which was connected to cyclone PIERRE at the western side, dominated the weather in western Germany with cool and cloudy air that was analyzed as sub polar sea air. While a day before the sun was shining for nine hours in most parts of the country, only regions in the east and south that were influenced by the anticyclone ERIKA reported sunshine durations of more than four hours on the following day. Cologne had got two hours of sunshine, Bad Lippspringe one hour and many towns by the North Sea not even an hour. Thus, Munich recorded maximum temperatures of 15C, Berlin 13C, but Westerland on the island Sylt only 5C. The weak occlusion with the characteristics of a cold front advanced east and crossed Germany over night. Until the next morning, Ingolstadt reported 5 l/m in 24 hours, Braunlage 2 l/m and Hamburg 0.8 l/m.

On the 17th of February, the low pressure system PIERRE still showed two cyclone centers. The center PIERRE I moved northeastwards in between Stockholm and Helsinki and the center PIERRE II was located in the north of Norway with an air pressure of below 1000 hPa. The weather front that crossed Germany the day before was reaching over Finland, Poland and ended over the Alps. One cold front of the depression center PIERRE II was moving westwards over the Norwegian coast, another warm front over Finland, which was connected to a cold front of a deep forward moving unnamed cyclone situated over Russia. In the cold maritime air mass maximum temperatures in Germany did not exceed 10C. Essen reported 7C, Dresden 8C, Rostock-Warnemnde 5C. The unstable cold air mass was partially leading to heavy snow fall on higher altitudes with 75 cm of snow in total at the station Brocken, although the precipitation was falling as rain later on. Also, Bavaria measured great quantities of rain like Kempten with 11 l/m or Munich with 16 l/m. Temperatures in Poland often only reached 3C like Warsaw, Kalisz or Wielun. Until 7 pm, the weather station in Mlawa reported 6 l/m, Kalisz 5 l/m and Gdov in Estonia 7 l/m.

On the next day, there was only one cyclone center named PIERRE. Situated over Archangelsk, the air pressure was lower compared to the day before. A weather front connected the center to another unnamed depression over Norway. A warm front was moving eastwards crossing Russia and ending at the Black Sea. Another warm front extended to the east. The weather fronts of the cyclone system continued with light rainfall and amounts that were mostly less than one liter in 24 hours. Nevertheless, the cyclone PIERRE replaced cold air mass over Russia with maritime air masses, so that maximum temperatures rose.

Forming only one center of low pressure, the depression PIERRE was located over Russia on its last days of existence on the meteorological map by the Berliner Wetterkarte. On the 19th of February the cyclone PIERRE deepened to an air pressure of 985 hPa. Its cold front was connected to the warm front of the cyclone QERKIN over Sweden. Until the following day, the depression PIERRE was moving northeastwards, so that the 20th of February was the last day the cyclone PIERRE was analyzed.

 

 

Geschrieben am 07.03.2017 von Natja Bublitz

Berliner Wetterkarte: 16.02.2017

Pate: Pierre Carrega