17th December 2010 by Optimus Prime

"The run up to Christmas 2010 looks very cold with many parts of the UK (particularly top and tail ends of the country) would have been covered by snow by the 25th. Indications are that Christmas day will be dry but very cold initially with a continental influence atleast momenterally covering eastern and southern parts of the UK. Low level surface cold from the east may lead to some misty conditions with freezing fog. After this high pressure may edge closer to the UK with only Northern Scotland having an ease of the very cold weather. New year looks dry at this stage."

I'm glad I entered that last year (I had a 'mild' feeling it might come in handy come December 2011 and the year 2011 in general) the CET difference between December 2010 (-0.7c) and December 2011 (Roughly 5.6c) isn't as astonishing as the reversal in synoptics perhaps.

December 2011 has, bar January, been one of the more wintrier months of 2011 and has continued in the spirit of Decembers since around 1995 in producing the most seasonal weather. Although this month can hardly be described as wintry it has in all conscience produced atleast one day of falling snow and a couple of frosts (very white frosts at that)

It does seem to be that strikingly cold Decembers (I'll use 1.7c or below as the baseline) are followed by a milder and more tranquil adversary. Some examples;

[b]December 1933 1.6c (3rd coldest 20th century)[/b]
[b]December 1934 8.1c (equal mildest with 1974)[/b]

[b]December 1950 1.2c (Second coldest of the 20th century)[/b]
[b]December 1951 5.5c[/b]

[b]December 1981 0.3c (coldest of the 20th century)[/b]
[b]December 1982 4.4c[/b]

[b]December 2010 -0.7c[/b]
[b]??December 2011 5.6c??[/b]

What is also often the case cold Decembers (above 1.7c) come in pairs and sometimes threes;

1916 1.9c
1917 2.3c

1927 2.1c
1928 3.4c

1961 2.2c
1962 1.8c
1963 2.6c

1995 2.3c
1996 2.9c

2008 3.5c
2009 3.1c
2010 -0.7c

Statistically significant? I doubt it but Chi squared would probably be of good method. Possibly degrees of freedom too.

It's patterns which produce the type of weather selected regions of the earth get. It can be quite safe to assume exceptional and unusual occurences of cold weather patterns can quite easily reverse but tend to stick around for some time. What's so unusual about present time is the fickleness of cold. Seems the cold never extends beyond the compounds of winter and that prolonged phases of recurring cold (2010 for example) are then followed by an extreme mild comback. On this basis it would be safe to assume mild active weather won't be going away anytime soon, not in long period anyway.

2010 8.83
2011 10.69c (assuming December at 5.7c)
9.76c average (+0.01c)

The deviation from the mean might give the inkling the significance of last years cold is almost in direct proportion to this years mild. In other words an extreme polar opposite are met and a balance has been addressed.

But in actual fact this years mild blows away last years cold in signficance. 2011 is likely to be the 2nd warmest year on record since 1900. 2010 was only the equal 9th coldest since 1900.