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How often should we expect a very cold December?


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A thought I've had recently is how often on average do very cold December's occur. Although my knowledge in this area is limited (I don't know the CET figures etc) my guess is somewhere in the region of about once every 15 years give or take. Although we had 2 in a row with 2009 and 2010 (though the former didn't really get going until fairly far into the month) the last before then was probably 1995 (though saying that 2000 had a pretty intense cold spell in the Christmas to New Year period). Before then there was 1981 which was 14 years prior. I'm not so sure before then but 15 years before then would have been in the mid 60s, so 1965 possibly? Though we know 1962 was cold though again the most brutal cold didn't come until quite late in the month. Anyway based on this idea, though it might not be the case maybe our next very cold December shouldn't be expected to at or around 2025. This is only an idea of course so it would be interesting to hear if anybody thinks there's anything in this or not.

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2 minutes ago, Mark wheeler said:

I expect one every year . I only remember 2 in my lifetime but probably missed a couple in my younger years .

 I would be happy with 1 in 5 that's not to much to ask is it ? 

:shok:

Well Mark, as I'm currently experiencing my 59th December, 1981 and 2010 are the only two that I can recall...Does one-in-thirty sound about right?:search:

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It's pot luck, there were 4 sub 1C CET Decembers in the 1870s, whilst from 1910 to 1925, December was warmer than the November, 8 times.

A December you hardly hear mention is the one in 1976. That had a CET of 2.0C, colder than December 1995 but it's a month that is rarely mentioned.

Edited by Weather-history
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19 minutes ago, Ed Stone said:

Well Mark, as I'm currently experiencing my 59th December, 1981 and 2010 are the only two that I can recall...Does one-in-thirty sound about right?:search:

I would agree although I wasn't living in the UK in 2010 so it would only be 1981...although December 1978 was quite snowy esp at the end.

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6 minutes ago, Mark wheeler said:

Actually my father said the year I was born December 27th 1978 was really cold with copious amounts of snow . So I've had 3 . Well just about .

I think 1978 was another December that didn't really get cold until the end of the month though. There's been quite a few December's like that over the years, but I'm really talking about one's that have been more consistently cold throughout. 2009 and 2000 are ones like that I mentioned but one's that are more or less cold from beginning to end are much rarer and from what I can tell occur on average once every 15 years or so, though some are more so than others. Like I say before 2010 which was very cold nationwide, we had 1995, which however was much colder in the north than the south, being especially so in Scotland. Before then was 1981 from what I can tell was very cold all over like 2010. As I say though it's just an idea.

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5 hours ago, Mark wheeler said:

Actually my father said the year I was born December 27th 1978 was really cold with copious amounts of snow . So I've had 3 . Well just about .

End of 78, 81 and 2010

Lots of snow ball fights at school end of dec 78 and then of course we had Jan 79

On 27 dec 1978 that was my sisters birthday she was 10 and i  use to keep detailed diaries then (being 13)  i mention in them a lot of snow. 

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They can happen at anytime. It's just about luck. 2010 was the coldest since...was it 1891? There were cold Decembers in 1981, 1995,1996, 2009 and 2010 (I'm 28 so am listing the ones which I know have occured in my lifetime. Maybe the next cold December will have a CET close to the CETs of those Decembers averaged out...just a thought. ☺

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December is rarely very cold in Britain because the Circumpolar Vortex tends to be at its strongest in late December: The Arctic (particularly NE Canada and Greenland) is very cold by this time whilst the North Atlantic still has considerable warmth and this creates the conditions for persistent deep cyclogenesis in the far North Atlantic with deep depressions racing east/NE in the vicinity of Iceland. In recent years the greater warmth of the northern North Atlantic has provided even more moisture in the air (to provide even more latent heat fuel as the air rises and condenses its moisture) to power greater depressions; the more northerly path of depressions following the retreated edge of Arctic ice demands of even stronger higher-latitude Westerlies to occur in to counteract the input of Westerly AAM elsewhere (due to the interaction of tropical and subtropical easterlies with the surface in low latitudes) to satisfy Conservation of Angular Momentum laws. That is because the Westerlies coming across the North Atlantic blow closer to the axis of the Earth's rotation. It is this strength of deep depressions-and attendant Westerlies- that has contributed to the devastating floods and storms seen in northern Britain in December 2015 and throughout the winter months (and nationwide) throughout Winter 2013/14

December is very unlikely to be very cold for the next few years and for the above reasons but there is an increased chance of something like December 1981 or December 2010 as the Grand Solar Minima gets underway over the next 15 to 20 years and more so should some of those Decembers follow years during which major volcanic eruptions occur with excessive amounts of dust and SO2 in the Stratosphere helping to cool the lower atmosphere earlier in the season in higher latitudes whilst stratospheric dust leads to absorption and warming of weak sunshine at elevation. Such a development during the coming Grand Solar Minimum may overwhelm the effects of increased CO2 - induced warming leading to a slight global cooling. More important such a development- warming of the Stratosphere in early winter at higher latitudes, and cooling below is much more likely to encourage high-pressure than low-pressure at high latitudes going into winter and set the scene for Sudden Stratospheric Warming type events. In this situation with stronger seasonal cooling setting in sooner along the margins of the Arctic- encouraged by more frequent north-easterly winds- the storm tracks would move into lower latitudes and the Westerlies would weaken (blowing as they would be, further from the axis of Earth's rotation, they would not need to blow strongly to counteract the frictional effects of tropical and polar easterlies so as to satisfy Conservation of Angular Momentum Laws). This would set the scene for much colder northerly and easterly airstreams to reach the UK in early winter.

Furthermore, if we are to get really cold weather in December, it is helpful if the QBO is in a strongly "easterly" phase over preceding months and the entire pattern of winds aloft should have strong Westerlies, if there are to be any at all, at the altitude and latitude of the Himalayas so that the strong mountain torque removes excess Westerly AAM before it reaches higher latitudes. None of this was the case going into winter in 2016/17.

Even during the coming Grand Solar Minimum we are likely to have to wait until after Christmas for serious cold to set in; the strong baroclinic gradient between the frigid NE Canada/Greenland and the relatively warm North Atlantic in December will continue- for the main- to ensure very severe wintry spells of any duration during December will remain rare in lowland Britain (i.e. a one-in-20 year occurrence).

On that note, just to wish you all a happy and peaceful Christmas (even without the snow). 

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December 2010, was an exceptional rare event, that depth of persistant cold highly anamolous. As Ian says, getting cold to bed itself in is far more difficult to achieve in December, compared to January and more so February, indeed March is the month most likely to produce a colder period of weather when the PV has relented its fury. Still the likes of 2000, show potent cold can come from nowhere for a short period at least - that came after the wettest autumn on record, and a very wet mild first half to December.

Had the pattern of October and much of Nov, come a month or so later, then this December could have been quite a cold one, locked on the colder side of the jet with very cold continental air invading the country, we weren't far off a cold one this year I think, it just didn't come off, the cold synoptics came too early..

 

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Having a very quick reccie on past Decembers you are really looking at aprox every 15 years a December averaging 2 deg or less.It does not always give a true picture as cold spells do not always coincide with an entire month so there are many others that have had cold spells spoilt by a mild spell.1981 and 2010 are standouts that people remember but earlier wintery Decembers being 1916,27,33,50,62and 1978.It is also worth noting that November is capable of a good winter but even more rare than December especially nov 1915[2.8 cet] and 1919.

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Attached is a graph of the December CET values through the years, with horizontal lines marking the 0C, 1C, and 2C values.

Cold Decembers were very frequent during the late 1600s, and also throughout the late 1700s to the 1890s; since then the frequency of sub-2C Decembers has become less frequent. Sub-1C Decembers are interesting in that, with the exception of 1981 and 2010, they all appear to have occurred during clusters. There clusters were 1673-1683 which saw 5 such Decembers; 1784-1796 which saw 3 such Decembers; the duo in 1844 and 1846; and the period 1870-1890 which also saw 5 such Decembers. (Perhaps we haven't waited long enough to see 2010 sit in another cluster...?)

To answer your question, since 1659, the occurrence of cold Decembers seems to have been fairly erratic. In the previous 100 Decembers however, 7 have registered as 2C or less (1916 just creeps in here). So that would give one every 14 years.

 

DecemberCET.jpg

Edited by Relativistic
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1 hour ago, Relativistic said:

Attached is a graph of the December CET values through the years, with horizontal lines marking the 0C, 1C, and 2C values.

Cold Decembers were very frequent during the late 1600s, and also throughout the late 1700s to the 1890s; since then the frequency of sub-2C Decembers has become less frequent. Sub-1C Decembers are interesting in that, with the exception of 1981 and 2010, they all appear to have occurred during clusters. There clusters were 1673-1683 which saw 5 such Decembers; 1784-1796 which saw 3 such Decembers; the duo in 1844 and 1846; and the period 1870-1890 which also saw 5 such Decembers. (Perhaps we haven't waited long enough to see 2010 sit in another cluster...?)

To answer your question, since 1659, the occurrence of cold Decembers seems to have been fairly erratic. In the previous 100 Decembers however, 7 have registered as 2C or less (1916 just creeps in here). So that would give one every 14 years.

 

DecemberCET.jpg

This  actually supports my suspicions that very cold December's are only likely once every 15 years give or take. Of course they were probably more frequent than that during the LIA. But I think (though it's by no means guaranteed and it could be sooner or later) that our next very cold December could be realistically expected around the mid 2020s. We'll see though of course and even if true it doesn't mean that very cold spells within December shouldn't be expected before then. Just that a consistently very cold December is possibly less likely before around then. Who knows though really, and as I say it's just a thought.

Edited by Walsall Wood Snow
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The biggest crumb of comfort for cold/winter fans is that despite the recent rapid deterioration and warming of December post 2010, December shows both the least warming and least loss of degree of cold compared to all of the other month in the christmas pudding.

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