December 2023 C.E.T. and EWP forecast contests -- start of 2023-24 contest year -- all welcome

[LetItSnow!]

Past couple years I’ve not really paid attention to the contest but for the 2024 year I do intend to. Going to wait until the 30th to make my guess but I do wonder if we could bag two chilly Decembers in a row. How cold are the opening days of December looking in the CET zone? All depends on snow cover and exact synoptics. Looking cold!

[summer blizzard]

5.6C, 74mm

Suspect this will be wrong given the outlook but i will stick with my normal methods. 

 

[NeilN]

3.6c and 21mm

[Shillitocettwo]

3.9.C and 51mm.

 

December will help avoid a clean sweep of above average CETs for 2023.

 

   A month that will behave surprisingly 2010 like for its majority, disruptive snow and some double digit minus nights even quite far South, at one point around the 18th the CET will be hovering around the freezing mark for the month, however a rather sickeningly mild spell will take over with a snap to 2015 behaviour with impressive transient snow as it does so. After delivering 20.3 C on the 23rd, with the CET rapidly shooting up, a very nondescript Twixmas of mildish dreary fog will set in to close out the year.

Edited November 27, 2023 by Shillitocettwo

[Roger J Smith]

On 25/11/2023 at 04:17, WYorksWeather said:

As I did in November, for those who prefer a visual aid, here are all of the December CET values.

The striking thing is just how large an anomaly both 2010 and 2015 were. 2010 being the first sub-zero December in more than 100 years, and 2015 being the warmest by a huge margin.

Legend:

Lighter blue / cyan is the 10-year trailing average (i.e. 2000 = average of 1991-2000)

Dark blue is the  30-year trailing average (i.e. 2000 = average of 1971-2000)

 

You can see that the 30-year average is slowly trending upwards, but the 10-year average is much more chaotic, with a much greater number of peaks and troughs.

I'll wait to deliver my own prediction until modelling is a bit clearer on early December.

I like the visuals but your data base only overlaps the daily data era 1772 to present, you could perhaps get the earlier monthly data for 1659 to 1771 to extend it back. If the graph above in quoted post were extended back you would see another peak around 1710-1739 and a cold interval centered on 1671-1700. I have all the graphs available too, on my excel file of CET data, so I could post them in future discussions. 

December got relatively quite cold in an interval from about 1841 to 1890 and was often coldest month of winters; that tendency actually appeared to shift even earlier with Nov taking a colder turn around decades 1901-1930. Then it was February often coldest in the period 1941-70. Recently it has been a case of which winter month sucked least, and the jury is still out on that one. It's strange that no Dec between 1677 and 1787, or 1797 to 1873, or (less strange) 1891 to 1980, was as cold as either 1981 or 2010. Those were intervals of 111, 87 and 90 Decembers that avoided going sub 0.2 C. 

This will be the 13th try since 2010 so you wonder how long this streak will be. 

Last Dec at 3.4 was coldest since 2010 so the comparable Dec futility benchmarks are:

Longest previous streak all at or above 3.0 __

16 1900-1915 (1906 was 3.0)

longest all above 3.0 is

13, 1982 to 1994, 3.4 in 1992 coldest tied by 1997 to 2009, 3.1 in 2009 coldest;

followed by 12, 1938 to 1949, 3.1 in 1946 coldest

Longest previous streak all at or above 2.0 __ 

31 _ 1684 to 1714 _ coldest 2.5 several Dec

22 _ 1743 to 1764 _ coldest 2.5 1759

23 _ 1893 to 1915 _ coldest 2.2 1899

28 _ 1982 to 2009 _ coldest 2.1 1995

 

[LetItSnow!]

The GFS run tonight interests me for many reasons, but one of them being how low the CET could go during that period up to at least the 11th. Oh dear, I’m getting excited. Never a good sign.  

[Roger J Smith]

The big blizzard in Russia looks like a scene from the 1940s. Isn't this exactly why the Nazis failed to over-run the Soviet capital in Nov-Dec 1941? They got stopped by winter not Stalin, who used the delay to get his forces properly armed. CET values for winter 1941-42 are 5.6, 0.9 and 0.2. It was in fact very mild in Britain in mid-Dec 1941, and only began to turn very cold after Christmas. 

For predictions I will go with

2.9 C and 64.7 mm

cold to dig in and resist a lot but not all of Atlantic's pushback. Winter storms could be epic around 26 to 28 Dec

Edited November 28, 2023 by Roger J Smith

[jonboy]

Going early for me and 3.2c and 71mm please

[Stationary Front]

Looks like the first third of the month may not get much above 3c, the next third maybe above average, which could take the CET to around 5c. Which leaves the final third? I really hope it goes below average again. So with that ‘hope’ I’ll go for a final CET of 2.8 please with 64mm 

[Leo97t]

4.5c and 60mm

[LetItSnow!]

Interesting to see the GFS resurrect the Scandinavian high idea. A fridgid first half to December is still in the game, and as pointed out by me, a southerly tracking jet means a lot of cold rain and not a super boost to the CET. Will wait to the 30th to make my guess but there is a possibility we could be colder than last year. Nervously exciting times for a coldie.

[I remember Atlantic 252]

5.7C and 112mm

first 5 days cold and below CET average, then an Atlantic powerhouse barrage from 6th, with possible days of record warmth for that certain date

[SummerShower]

4.8C, 56mm.

A mixed month with some rain, some sun, some cloud, some spells of cold, some mild and maybe windy at times.

[WYorksWeather]

On 27/11/2023 at 21:30, Roger J Smith said:

I like the visuals but your data base only overlaps the daily data era 1772 to present, you could perhaps get the earlier monthly data for 1659 to 1771 to extend it back. If the graph above in quoted post were extended back you would see another peak around 1710-1739 and a cold interval centered on 1671-1700. I have all the graphs available too, on my excel file of CET data, so I could post them in future discussions. 

December got relatively quite cold in an interval from about 1841 to 1890 and was often coldest month of winters; that tendency actually appeared to shift even earlier with Nov taking a colder turn around decades 1901-1930. Then it was February often coldest in the period 1941-70. Recently it has been a case of which winter month sucked least, and the jury is still out on that one. It's strange that no Dec between 1677 and 1787, or 1797 to 1873, or (less strange) 1891 to 1980, was as cold as either 1981 or 2010. Those were intervals of 111, 87 and 90 Decembers that avoided going sub 0.2 C. 

This will be the 13th try since 2010 so you wonder how long this streak will be. 

Last Dec at 3.4 was coldest since 2010 so the comparable Dec futility benchmarks are:

Longest previous streak all at or above 3.0 __

16 1900-1915 (1906 was 3.0)

longest all above 3.0 is

13, 1982 to 1994, 3.4 in 1992 coldest tied by 1997 to 2009, 3.1 in 2009 coldest;

followed by 12, 1938 to 1949, 3.1 in 1946 coldest

Longest previous streak all at or above 2.0 __ 

31 _ 1684 to 1714 _ coldest 2.5 several Dec

22 _ 1743 to 1764 _ coldest 2.5 1759

23 _ 1893 to 1915 _ coldest 2.2 1899

28 _ 1982 to 2009 _ coldest 2.1 1995

 

The issue with going back before the daily era is my understanding is that data that early are somewhat less reliable. From a bit of reading, some studies have opted actually to drop that data. Quality issues are apparently particularly bad before 1722, with figures quoted to a lower level of precision, and some non-instrumental data used.

The daily data is maintained as a single dataset, so I take that as a mark of some level of guaranteed quality / consistency. The other advantage to keeping the data all at the same time horizon is that I can also do analysis at any level very quickly, whether it be averaging over multiple months / seasons, or looking within a month.

I'll leave the pre-daily data insights to you I think (you seem to have a good method anyway!).

[Roger J Smith]

I can't say with any assurance that the CET records 1659 to 1771 are accurate or as accurate as later, but they do see to correspond to any other evidence available. There's martin Rowley's research into weather related historical evidence that he ties to CET values, and it all appears to fit reasonably well. You can see all that on his site, Premium Weather, just google UK weather 1700-1749 (as one example, he has it organized by half centuries) and it will be the first return on your search. And he has historical stuff going back into the period before 1,000 AD. It gets very anecdotal but at least we know which years were hot and which were cold, and to some extent wet and dry also. 

I would rate the CET as "moderately reliable" before 1720 and probably almost as reliable as after 1772 between 1721 and 1771, but as you say, we don't really know for sure and can never know, it's all we will have as a rough guide unless we get people returning from the grave and even they would not have the benefit of knowing our modern methods of measurement necessarily. 

[DR(S)NO]

Thanks to you Roger and J10 for running the comp. A great bit of fun for the Netweather Community.

 

my guess for Dec23

4.0c and 100mm thank you

[feb1991blizzard]

5.3c and 119mm please

[emmett garland]

3.7 and 81mm please Roger

[reef]

Slightly milder and drier than average.

5.8C and 87mm.

[damianslaw]

December 2015 was ridiculous! The next mildest 1.5 degrees lower!

Edited November 29, 2023 by damianslaw

[WYorksWeather]

Going to try to make a decision now - waiting a few days hasn't really helped! If the models come up with a clearer idea tomorrow I might change it again, but if not, this one will stand.

I'm going to go for a cold first 10 days, near 3C on the CET.

The middle 10 days I'll say the Atlantic kicks in and we go mild, near 7C.

The last 10 days I'll say will feature a gradual descent back into cold, with an average of 4C but mild at the start and very cold by New Years' Eve.

Put that together, I'll go for an average of 4.7C.

Slightly above average on 1961-1990, and therefore the first year to see all 12 months above the 1961-1990 average.

EWP, I'll go for a dry first 10 days, then a very wet 10 days, then an average-ish last 10 days, so coming out slightly above average. I'll go with 115mm.

[damianslaw]

I'll hold out until tomorrow, not expecting the models to be very helpful. Expecting a very unpredictable month.. could be a lot colder than might be anticipated..

[Don]

Would normally hold out until the last day of the month but will post now as will be busy tomorrow.

I really wouldn't like to call December as was initially expecting it be fairly mild but haven't a clue now!  However, I will go with 5.4C and 130mm please.

[Daniel*]

4.3c and 80mm thanks 

[Frigid]

5.2c and 135mm. Thanks