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Extreme Jet Stream Pattern Triggers Historic European Floods
Funny, there's that "arctic warming --> jet stream loopiness --> extreme weather hilarity" theme again.
The primary cause of the torrential rains over Central Europe during late May and early June was large loop in the jet stream that developed over Europe and got stuck in place. A "blocking high" set up over Northern Europe, forcing two low pressure systems, "Frederik" and "Günther", to avoid Northern Europe and instead track over Central Europe. The extreme kink in the jet stream ushered in a strong southerly flow of moisture-laden air from the Mediterranean Sea over Central Europe, which met up with colder air flowing from the north due to the stuck jet stream pattern, allowing "Frederik" and "Günther" to dump 1-in-100 year rains. The stuck jet stream pattern also caused record May heat in northern Finland and surrounding regions of Russia and Sweden, where temperatures averaged an astonishing 12°C (21°F) above average for a week at the end of May. All-time May heat records--as high as 87°F--were set at stations north of the Arctic Circle in Finland.
...
If it seems like getting two 1-in-100 to 1-in-500 year floods in eleven years is a bit suspicious--well, it is. Those recurrence intervals are based on weather statistics from Earth's former climate. We are now in a new climate regime with more heat and moisture in the atmosphere, combined with altered jet stream patterns, which makes major flooding disasters more likely in certain parts of the world, like Central Europe. As I discussed in a March 2013 post, "Are atmospheric flow patterns favorable for summer extreme weather increasing?", research published this year by scientists at the Potsdam Institute for Climate Impact Research (PIK) in German found that extreme summertime jet stream patterns had become twice as common during 2001 - 2012 compared to the previous 22 years. One of these extreme patterns occurred in August 2002, during Central Europe's last 1-in-100 to 1-in-500 year flood. When the jet stream goes into one of these extreme configurations, it freezes in its tracks for weeks, resulting in an extended period of extreme heat or flooding, depending upon where the high-amplitude part of the jet stream lies. The scientists found that because human-caused global warming is causing the Arctic to heat up more than twice as rapidly as the rest of the planet, a unique resonance pattern capable of causing this behavior was resulting. According to German climate scientist Stefan Rahmstorf, "Planetary wave [jet stream] amplitudes have been very high in the last few weeks; we think this plays a role in the current German flooding event." More rains are in store for the flood area through Monday, then the blocking pattern responsible for the great 2013 Central European flood is expected to disintegrate, resulting in a return to more typical June weather for the next two weeks.
http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=2432
...
If it seems like getting two 1-in-100 to 1-in-500 year floods in eleven years is a bit suspicious--well, it is. Those recurrence intervals are based on weather statistics from Earth's former climate. We are now in a new climate regime with more heat and moisture in the atmosphere, combined with altered jet stream patterns, which makes major flooding disasters more likely in certain parts of the world, like Central Europe. As I discussed in a March 2013 post, "Are atmospheric flow patterns favorable for summer extreme weather increasing?", research published this year by scientists at the Potsdam Institute for Climate Impact Research (PIK) in German found that extreme summertime jet stream patterns had become twice as common during 2001 - 2012 compared to the previous 22 years. One of these extreme patterns occurred in August 2002, during Central Europe's last 1-in-100 to 1-in-500 year flood. When the jet stream goes into one of these extreme configurations, it freezes in its tracks for weeks, resulting in an extended period of extreme heat or flooding, depending upon where the high-amplitude part of the jet stream lies. The scientists found that because human-caused global warming is causing the Arctic to heat up more than twice as rapidly as the rest of the planet, a unique resonance pattern capable of causing this behavior was resulting. According to German climate scientist Stefan Rahmstorf, "Planetary wave [jet stream] amplitudes have been very high in the last few weeks; we think this plays a role in the current German flooding event." More rains are in store for the flood area through Monday, then the blocking pattern responsible for the great 2013 Central European flood is expected to disintegrate, resulting in a return to more typical June weather for the next two weeks.
http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=2432