Extreme Weather in parts of the world
The United States was gripped by a cold wave 7-8 January, whilst much of Europe has seen unusually mild weather, and Australia was gripped by a heatwave. The conditions were accurately predicted in advance (in some cases, by more than one week) by meteorological services.
The U.S. National Weather Service said that on 7 January, every state in the lower 48 had somewhere that was below freezing. Even Northern Florida, the Gulf Coast, and Texas had several temperatures in the 20s Fahrenheit or lower. The wind chill factor made it feel even colder.
This was because of the Polar vortex. In the winter a deep reservoir of cold air becomes established through the atmosphere over the Arctic because of the lack of sunlight. This is usually held over high latitudes by the jet stream.
What is happening over North America is that the jet stream has weakened and moved southwards. This allowed the reservoir of cold air to move southwards across the US, resulting in extremely low temperatures.
In response to commentary about the links between the cold snap and climate change, President Obama's Science and Technology Advisor, Dr. John Holdren, had the following to say:
«If you’ve been hearing that extreme cold spells disprove global warming, don’t believe it. No single weather episode can prove or disprove global climate change. Climate is the pattern of weather geographically and over seasons. A growing body of evidence suggests that the kind of extreme cold experienced by the United States is a pattern we can expect to see with increasing frequency as global warming continues. «
«I believe the odds are that we can expect as a result of global warming to see more of this pattern of extreme cold in the mid latitudes and some extreme warm in the far north.»
Much of Europe has experienced exceptionally mild winter so far.
Météo-France reported that on Wednesday, maximum daily temperatures were 5 to 9 degrees Centigrade above the January norm. On Thursday morning, the minimum temperature recorded at 7 a.m. was 17.9 °C in Biarritz
and 19.2 °C in Bustince – temperatures more typical of summer.
Since the start of December the UK has seen a prolonged period of particularly unsettled weather, with a series of storms tracking in off the Atlantic bringing strong winds and heavy rain. The UK’s Met Office suggests that December 2013 was the stormiest December in records dating back to 1969 and was one of the windiest calendar months for the UK since January 1993. December was also a very wet month across the UK, particularly in Scotland where it was the wettest December and wettest month overall in the records dating back to 1910.
Much of Russia has witnessedvery much above normal temperatures reaching +9°C anomalies during the week of 29 Dec-4 Jan, Currently it is still warm. For example Moscow temperature Thursday averaged 2°C while January daily average temperature is -9°C. Parts of Scandinavia have also been unusually mild, as have Austria, Germany and Switzerland.
There is a connection between the observed large scale temperature anomalies over the northern hemisphere and the so-called planetary waves. These explain the observed atmospheric disturbances in pressure and wind patterns which affected large geographical domains and resulted in opposite temperature signals and different extreme precipitation features across the Atlantic.
The Bureau of Meteorology of Australia said that a significant heatwave affected much of the central and eastern interior of Australia over the New Year period in late 2013/early 2014. The heatwave was not as extensive or as prolonged as the heatwave of January 2013, and was not associated with destructive fires to the same extent, but was nevertheless highly significant with substantial areas having their hottest day on record. The first stage of the heatwave developed from 27 December, when very high temperatures occurred on the Nullarbor, including record high temperatures for December at Eucla and Forrest near the Western Australia-South Australia border. Over the next three days the focus of the heat moved to the southern and central interior of Queensland, where a few locations had their hottest day on record on either 29 or 30 December.
Australia had its hottest year on record in 2013.
Parts of Western Australia and South Australia are expected to experience heatwave conditions over the weekend, according to the Bureau of Meteorology. With temperatures recorded in the Pilbara over the last two days in excess of 48 degrees, it's highly likely many areas in Western Australia will exceed 44 degrees over the next couple of days.
Argentina has also witnessed one of the worst heatwaves on record at the end of December.
For more information on weather and climate extremes see http://wmo.asu.edu/