Cold Air Outbreak: 16-20 December 2009
A cold air outbreak during the second half of December 2009 brought mayhem to Western Europe and Croatia.
A Cold Air Outbreak directed by a strong anticyclone near Greenland directed polar air towards Europe. With the still relative warm waters of the North Sea and the genesis of several small scale disturbances over Scandinavia and Germany the ingredients were in place for many centimeters of snow in the UK, Netherlands and Germany.
The largest impacts the snow brought were experienced from 16 to 20 December. The largest railway station in the Netherlands (Utrecht CS) was closed on 17 December due to snowfall leaving thousands of passengers stranded. During the morning rush hour of 18 December there was a record breaking 671 kilometers of traffic jam. In England the snowfall had also lead to chaos when motorists were stuck on the A21 during the evening and night of 17 to 18 December. The next night five international EUROSTAR trains were stuck in the tunnel under the English Channel leaving 2.000 passengers trapped for 16 hours.
From a meteorological point of view this cold air outbreak is interesting as many parts of Europe were affected and that there were different conceptual models responsible which can be distinguished using satellite and numerical weather data. All of these are described in detail in this case study.