After being reminded about this a couple of weeks ago I decided to have a look at the stats back to 1806 and see what the results are.

If there is a run of cold days (3.3C or less) around mid-month the chance of an average to colder than average January and February is 94% and 74% respectively. The chance of an average to colder than average March is 96%. Also notable is that the chance of a severe spell in January (4C colder than normal) is 30%.

The full blog post can be found here. http://wp.me/p2VSmb-wO

On Wednesday, December 10, 2014 1:53:07 PM UTC, Scott W wrote:
After being reminded about this a couple of weeks ago I decided to have a look at the stats back to 1806 and see what the results are.

If there is a run of cold days (3.3C or less) around mid-month the chance of an average to colder than average January and February is 94% and 74% respectively. The chance of an average to colder than average March is 96%. Also notable is that the chance of a severe spell in January (4C colder than normal) is 30%.

The full blog post can be found here. http://wp.me/p2VSmb-wO

=========

Interesting as far as it goes - but what temperature is this? CET? Or one location's maximum temperature? Or 24-hour average?

In any case it looks like being slightly milder just after mid month. If the measure is maximum temperature I don't at see that below 3 or 4 deg C for most.

It makes a kind of sense because mid Dec-Jan regimes are often linked, so a cold block, for example, in mid December would more often than not also be January's characteristic.

Stephen.

On Wednesday, 10 December 2014 14:24:10 UTC, Stephen Davenport wrote:

It makes a kind of sense because mid Dec-Jan regimes are often linked, so a cold block, for example, in mid December would more often than not also be January's characteristic.

This is what I was thinking. Cold air in the UK in December, especially prolonged cold suggest it's come from the East which in itself implies that the "East" has cooled down quickly and provide a source of cold and I'd imagine that a colder East with an existing high pressure/cold pool might be prone to more stagnation during the remainder of the winter.

Richard

Richard Dixon wrote:

On Wednesday, 10 December 2014 14:24:10 UTC, Stephen Davenport wrote:

It makes a kind of sense because mid Dec-Jan regimes are often linked, so a
cold block, for example, in mid December would more often than not also be
January's characteristic.

This is what I was thinking. Cold air in the UK in December, especially
prolonged cold suggest it's come from the East which in itself implies that
the "East" has cooled down quickly and provide a source of cold and I'd
imagine that a colder East with an existing high pressure/cold pool might be
prone to more stagnation during the remainder of the winter.

Richard

One that perhaps supports your argument in a negative way is Dec 1981 to Feb
1982. Dec 81 was extremely cold in the SE. At Chalfont St Giles the mean daily
max was only 2.8 and there were 6 days with the max below zero. There were 23
days with snow lying at 0900. It would easily have triggered Colin Finch's rule
yet Jan/Feb 82 were rather mild overall, apart from the 2nd week in January
which was cold with a major snowstorm on the 8th.

The cold in Dec 81 was not the result of in incursion of easterly air. If I
recall correctly it resulted mostly from northerly plunges behind lows tracking
SE across the country. It was a very cyclonic month, not what you would
initially think would produce severe cold in December. There was therefore no
pre-existing block to persist into Jan/Feb.


--
Norman Lynagh
Tideswell, Derbyshire
303m a.s.l.
http://peakdistrictweather.org

Daily Tmax at Greenwich

On Wednesday, December 10, 2014 3:14:27 PM UTC, Scott W wrote:
Daily Tmax at Greenwich

=====

Thanks.

In message ,
Scott W writes
After being reminded about this a couple of weeks ago I decided to have
a look at the stats back to 1806 and see what the results are.

If there is a run of cold days (3.3C or less) around mid-month the
chance of an average to colder than average January and February is 94%
and 74% respectively. The chance of an average to colder than average
March is 96%. Also notable is that the chance of a severe spell in
January (4C colder than normal) is 30%.

The full blog post can be found here. http://wp.me/p2VSmb-wO

Those are remarkably high percentages. The biggest surprise is that it
should be such a strong pointer for as far ahead as March, and - oddly -
stronger than for February.
--
I'm not paid to implement the recognition of irony.
(Taken, with the author's permission, from a LiveJournal
post)

On 10/12/2014 15:14, Scott W wrote:
Daily Tmax at Greenwich


Thanks Scott, interesting stuff. I think you just have to take it on
face value and not get to hung up on detail. Not convinced of a pre
Christmas cold snap atm.

--
Keith (Southend)
"Weather Home & Abroad"
http://www.southendweather.net
Twitter:@LawnscienceEssx

On Wed, 10 Dec 2014 17:09:18 -0000, John Hall
wrote:

In message ,
Scott W writes
After being reminded about this a couple of weeks ago I decided to have
a look at the stats back to 1806 and see what the results are.

If there is a run of cold days (3.3C or less) around mid-month the
chance of an average to colder than average January and February is 94%
and 74% respectively. The chance of an average to colder than average
March is 96%. Also notable is that the chance of a severe spell in
January (4C colder than normal) is 30%.

The full blog post can be found here. http://wp.me/p2VSmb-wO

Those are remarkably high percentages. The biggest surprise is that it
should be such a strong pointer for as far ahead as March, and - oddly -
stronger than for February.

If it's cold in December, reckon mostly likely we're in for a long winter.
(sucks on straw)

--
Bah, and indeed, Humbug

Scott. I am not sure how you have arrived at those figures. Using the values
on the link you gave, and taking my own average monthly mean temp for the
periods 1882 to 1990 as an approximation, I find that for the years you
list, the Dec cold spells were followed by:
Normal (anom +1 to -1) Jan 38%, Feb 24%, Mar 34%
Cold (anom colder than -1) 48%, Feb 34%, Mar 32%
Mild (anom warmer than +1) 14%, Feb 42%, Mar 34%
So the 38 minus rule in Dec was followed by an average or warmer Jan in 52%,
Feb in 66% and Mar in 68%. I can see no useful peredictave value in that.

--
Bernard Burton

Wokingham Berkshire.

Weather data and satellite images at:
http://www.woksat.info/wwp.html

"Scott W" wrote in message
...
After being reminded about this a couple of weeks ago I decided to have a
look at the stats back to 1806 and see what the results are.

If there is a run of cold days (3.3C or less) around mid-month the chance of
an average to colder than average January and February is 94% and 74%
respectively. The chance of an average to colder than average March is 96%.
Also notable is that the chance of a severe spell in January (4C colder than
normal) is 30%.

The full blog post can be found here. http://wp.me/p2VSmb-wO



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