Omegalage

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Diagram of an omega location

The Omegalage , also Omegahigh , is a weather situation that is characterized by a large high pressure area , which in turn is flanked by two high troughs , one to the west and one to the east. This constellation is stable over comparatively long periods of time, both in the high pressure and in the low pressure range. The resulting printed structure is reminiscent of the Greek capital letter Omega and therefore takes its name.

meteorology

300-hPa - high winds June / July 2015 (weekly average): clear low to the west, two currents superimposed to the east
Summer 2010:
Global weather conditions as the causal link between the floods in Pakistan and Central Europe and the forest and peat fires in Russia .
Map of temperature anomaly summer 2003 to 1971–2000: The shape of the omega is clearly evident from the zonal temperature gradient, as is the eastern stable low. The focus on the west side of the Omega is based on additional south-west warm air masses.

Since, seen from above, the high that determines the omegalage rotates clockwise and the two lows counterclockwise, all three reinforce each other and block each other in the west drift , so that the omegalage is characterized by a certain stability. A weather forecast (“no change in sight”) over a longer period than the usual three to six days is possible.

  • In the high pressure area, a summer omegalage creates a typical fine weather situation with pronounced dryness and warmth up to heat waves and droughts . While a south-westerly, i.e. warm, current on the front (northern hemisphere: eastern edge) of a low is the normal case, it is characteristic of summer omegalages that the warm air circles the high core to the north without any particular cooling, so that an unusual warm north-westerly to north wind at the eastern edge of the high prevails.
  • In winter, on the other hand, omegalages often lead to very low temperatures and cold waves , because the low east of the blocking high forces polar cold air into the high-pressure areas with good weather, which are also cooled by radiation. Then there are strikingly large temperature differences to the warm air area lying west of it in the south current.
  • In the area of ​​the two low pressure areas, however, omegalage - in summer and winter - leads to heavy rainfall and thunderstorms.

Omegas are not completely stationary, but move slowly. This means that a long period of good weather can be followed by a long period of bad weather and vice versa.

Omegas across Central Europe

  • August / September 2002: After the flood disaster on the Elbe in early August 2002, it was hot, sunny and dry from mid-August to mid-September.
  • In the summer of 2003 an omegalage led to the 2003 heat wave in Europe ; Already in the run-up to this summer there were several omegalages since December 2002 after the inconsistent autumn weather in 2002, this led to a cold, dry winter 2002/2003, especially in northern and eastern Germany, and several dry periods in spring and early summer 2003.
  • Autumn 2005: After a rather changeable summer, several omega stores from the end of August to mid-November led to a very warm and sunny late summer and autumn, followed by a sudden onset of winter with snow chaos in Münsterland .
  • Summer 2006: Before the soccer World Cup 2006 it was too cold and rainy, during the World Cup - with a July deviation of more than 5 K from the mean - it was clearly too warm and too dry, then again too cold and rainy. In the first week of June and the first week of August there was a change in weather.
  • In April 2007 , after a very long period of pre-weathering with above-average temperatures, an omegalage was jointly responsible for three records: It became the sunniest, warmest and driest April in Germany since the German Weather Service began recording.
  • May 2008 : After unstable weather in March and April 2008, an omegalage took place at the end of April. This led to the driest May, especially in East Germany, and continued into June.
  • April 2009 : After the cold winter of 2008/2009 and a damp and changeable March 2009, an omegalage started around March 29th. As in 2007, it led to a very warm, dry and sunny high spring with almost summery weather at Easter and other summer days at the end of April / beginning of May and ended after five weeks on May 3rd.
  • Spring 2010: Floods , blocked Vb weather conditions over Eastern Europe
  • Spring 2011: After a changeable winter 2010/2011 with the record-breaking cold December 2010 and the mild, humid January 2011, several high pressure situations developed from mid- February 2011 . This weather situation again led to an extremely warm April and an overall dry and sunny spring 2011. A thunderstorm period at the beginning of June ended this weather situation.
  • Autumn 2011: After a rather changeable and stormy summer 2011, there was an increasing formation of high pressure areas over Central Europe from mid-September. These led to heat records at the beginning of October, and in the following period they showed an increasingly blocking character with the peak in the driest November for over 100 years. November was still very sunny, apart from the foggy regions, and very mild due to the inversion weather at higher altitudes. The omegalage ended abruptly at the turn of the month between November and December.
  • Beginning of 2012: After a pronounced westerly wind in December 2011 and early January 2012, there was again increasing high pressure from mid-January. As is typical of the season, this led to an increasing cooling of the air mass and at the beginning of February to the cold spell in Europe in 2012 . Even after the frost period subsided in mid-February, the influence of low pressure remained only weak, high pressure situations regenerated again and again and led to a very dry March with frequent inversion weather conditions, but also regionally sunny and already spring-like warm weather.
  • July / August 2014: An omegalage caused continuous rain and flooding in parts of Switzerland. At the same time, sunny, but mostly humid and thunderstorm summer weather prevailed in northern and eastern Germany for weeks.
  • End of June to August 2015 : In Germany, in the main stream of the Omegalage, an all-time temperature record of 40.3 ° C was measured.
  • Summer 2018 : The hot summer 2018 was mainly caused by an omega location.
  • June 2019 : Heat wave with over 45 ° C in southwest Europe (all-time temperature record in France)

Web links

Individual evidence

  1. ↑ SF Tagesschau August 8, 2010: Fires and floods: Extreme weather conditions are interrelated
  2. ↑ see Lionel Peyraud (German translation: Jacques Ambühl): Atmospheric blockings ( Memento from December 4, 2011 in the Internet Archive ) . August 19, 2010. MeteoSwiss → Current weather information
  3. ↑ https://web.archive.org/web/20070503131907/http://home.arcor.de/chrisi091984/juni_2006.htm
  4. ↑ https://web.archive.org/web/20071001062334/http://home.arcor.de/chrisi091984/august_2006.htm
  5. ↑ Not just natural causes: Slowed jet streams fuel natural disasters . In: weather.com , August 20, 2019. Retrieved April 17, 2019.
  6. ^ Özden Terli : President of the DWD - "We can now experience climate change live" . In: heute.de , May 3, 2019. Retrieved May 3, 2019.