Cold and frosty December

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  • Cold and frosty December
    12.12.2008 09:26

    "Everything was white; and the hedges looked as though they had grown old in the night. Everything glistened and all was still; the whole country was like Sleeping Beauty's park."

    The UK has certainly had more than its fair share of cold, frosty and occasionally snowy weather over the last two or three weeks and this short description of a frosty morning in 1925 by writer Vita Sackville-West sums up the scenes that some of us have been waking up to.

    Very cold nights during the weekend of December 6 and 7, coinciding with a gentle increase in moisture content from the west, resulted in a heavy hoar frost on the Sunday and Monday mornings.

    Looking at this cold spell in a wider context, the Central England Temperature (a long running temperature series based on temperature observations from several weather sites in the English Midlands) for the first 10 days in December is currently at 1.8C. This is nearly 4C colder than the average, quite a considerable shift from the average.

    So, why has it been cold for so long? This can be explained by the track of the jet stream - a narrow but very strong zone of winds at high altitudes which snakes its way around the middle latitudes of the Northern Hemisphere (there is also one at similar latitudes in the southern hemisphere).

    Persistent anomalies in the jet stream's track can often result in the weather at the surface becoming rather distorted from the climatologically mean.

    In this case the jet stream has predominantly been located well to our south and south-west over the past few weeks, preventing milder airmasses from the south-west sweeping across our shores.

    Instead, the position of the jet stream has allowed individual weather systems to feed cold north or north-westerly winds across the UK, with several waves of cold and also unsettled conditions sweeping over many areas.

    Taking a look into Europe, an anomalous southerly track of the jet stream has also been responsible for allowing many of the Alpine Ski resorts to have an excellent start to the 2008/2009 season.

    From the last 10 days in November right through into the first week in December, several cold plunges of air have pushed southwards from Scandinavia and the Arctic right across the Alps.

    These have tended to coincide with periods of very unsettled weather across southern parts of Europe and the Mediterranean, producing heavy and often frequent periods of snow over the Alps.

    A glance at the snow reports across many of the main Alpine resorts confirm that they have excellent conditions with good powder and many of their lifts and ski runs open.

    Resorts like St Moritz, Val Thorens, Val d'Isere, Meribel and Zell am See all have at least 100cm on the upper runs and more than 15cm on the lower runs.

    With more heavy snow expected to develop over the Alps again during the weekend, a substantial base layer of snow looks likely to be established and this bodes well for both the busy Christmas period and the 2008/2009 season as a whole.

    The only problem that skiers may possibly face is having too much snow falling during the daytime, but they can hardly complain.

    By: Matt Dobson