Author
Jarno Schipper - ZAMGAdrie Huiskamp - KNMI
Introduction
The case study deals with the snowfall over the Netherlands in the first week of March 2005. The development and the onset to this snowing event is pictured using various Meteosat 8 channels and RGBs as well as with the help of several NWP parameters. Up to 50 cm of snow were recorded. The mini case studie is further supplemented with a chapter "interactive overlays". In this chapter you can yourself overlay various numerical parameters on the corresponding satellite imagery. Through this interactive way you can reconstruct the case and exercise with it. The case was proposed by Meteoconsult in the Netherlands to EUMeTrain. If you think you can contribute to EUMeTrain by providing us dates of interesting case studies which happened in your region of interest, we encourage you to please write us using the above e-mail address.
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| Airmass RGB - 2nd March 2005:00 UTC - Frontal zone lies over the Netherlands. |
Synoptic situation
On February 27th a polar airmass was governing the Netherlands. It moved in from the North East. The maximum temperature of this airmass was around 0° degrees. During the night of 27th on 28th temperature fall even lower with temperatures under 0° degrees. This air was extremely dry with a dew-point temperature of -10° degrees. From the North two depressions entered the area of the Northsea on the 28th. The first depression moved over Danmark and moved further into northern Germany. The second one moved over England and then further into the Netherlands.
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| Surface chart 1st March 2005: 06UTC | Surface chart 2nd March 2005: 06UTC | Surface chart 4th March 2005: 06UTC |
The surface flow was southwesterly, meaning that except for the islands and Northwest Holland the dominant flow was over land. In these situations where snow is likely to fall the source of the air at the surface is of uttermost important. Eventhough it was the first week of March, the cold and dry air does not heat that fast over land than that it does over 7 degrees warm Northsea water. In the lower troposphere the warm air from the west and northwest glided over this cold polar air from the southwest creating a zone of convergence. This continues gliding of warm air over colder air caused the severe snowfall. This can also be seen in the veering of the wind with the height in the following figure.
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| Tephigram: 02 March 2005: 12UTC - source KNMI |
Remarkable was that this zone of upgliding air was stationary for about 15 hours, a so-called deformation zone.
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| Height of snow: 02 March 2005 - source VWK and KNMI |
During the passage of a ridge of high pressure in the night form the 3rd on 4th of March a low pressure system over the Northsea moved south. On approach of this system the wind again turned to south, to southwest. The snow layer and weather conditions (clear sky, weak ridge of high pressure) favoured significant cooling of the surface layer, leading to a minimum temperature of -20.7°C on 4 March in Marknesse. This set yet another record, for the lowest temperature in March (source Theo Steenbergen). In the early hours of the 4th cloudiness increased and in the afternoon the first snowfall was reported. The amount of snow however was far less thatn that of 2 days prior.
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| Height of snow: 04 March 2005 - source VWK and KNMI |
IR Imagery (Meteosat 8 channel 10.8): time sequence
This chapter shows and briefly describes the development in a sequence of 3-hourly images.
WV Imagery (Meteosat 8 channel 6.2): time sequence
In the following chapter the cloud configurations can be better related to the upper level dynamics using Meteosat 8 - WV6.2 channel.
Meteosat 8 - Airmass RGB: time sequence
The development and especially the physical background is pictured using the Airmass-RGB. The satellite images are each time 3 hours apart.