CET v2.0 removed the well-known December missing 5.9 -- so now what is the missing CET value closest to normal?

[Roger J Smith]

It was a well-known and celebrated oddity of the CET (legacy) record that in all the years of record (1659 to 2021), no December had ended up on 5.9 C. It seemed inevitable that it would fall, in an era of warming climate, as normal values crept ever closer to 5.9; no other month had a missing value anywhere near that close to the median of all values. But v2.0 removed the odd missing value and created three instances of 5.9. This got me to investigating what value of v2.0 CET is the closest to the median of all values. 

Here's the full list of missing CET values on either side of the average. The table shows the extremes in brackets -- those extremes of course do exist, all the numbers in between them have no instances. The two numbers closest to the middle of the table for each month are the two closest to the median or long-term average. The value shown for each month beside its three-letter abbreviation is the median of all values which is similar to but not necessarily equal to the long-term average. Modern 30-year normal values are often 0.5 to 1.0 C higher than these, which means that it will be more likely to break higher missing values than lower missing values at equal points from these medians. At the end of the table I identify the two values that have replaced Dec 5.9 as closest to average but still missing ...

Just to walk the reader through what we're talking about here, looking at January, the extremes in v2.0 are -3.1 (1795) and 7.6 (1916). The median value is 3.5. All the other numbers are CET values that have not yet happened in the v2.0 revised records. For example, none of the values -2.7 to -2.2 have occurred, and various others until reaching -0.5 which becomes the closest "cold missing CET" to the median. All the other values from -0.4 to 7.1 have at least one example. Near the top end, 7.2, 7.4 and 7.5 are the only "warm missing CET" cases. 

If no values are missing (example, May cold values) then the first cold value missing would be 0.1 below the extreme (in this case 8.4).

 

(extreme) __ Colder than average, no examples ___ Month (median) ___ Warmer than average, no examples ___ (extreme)

(-3.1) __ -2.7 to -2.2, -1.9 to -1.7, -1.3,-1.2,-1.1,-0.5 ___ JAN 3.5 ____ 7.2, 7.4, 7.5 (7.6)

(-1.9) _ -1.5 to -1.1, -0.9, -0.8, -0.6 to -0.3, -0.1, 0.2, 0.3, 1.1,1.3 __ FEB 4.0 __ 7.4, 7.6, 7.7, 7.8 (7.9)

(1.0) __ 1.1, 1.3 to 1.7, 2.2, 2.4, 2.6 ___________________ MAR 5.3 ___ 8.4 to 8.7, 8.9, 9.0 (9.2)

(4.7) __ 4.8 to 5.1, 5.3, 5.6 ____________________________ APR 8.0 ____ 10.4, 10.7 to 11.1, 11.2 to 11.8 (11.9)

(8.5) __ no values are missing 8.5 to median __________ MAY 11.2 ____ 13.2, 14.0 to 15.0 (15.1)

(11.5) __ 11.6, 11.7 ___________________________________ JUN 14.3 ____ 16.3, 16.5, 16.7, 17.0, 17.2, 17.4 to 17.9, 18.1 (18.2)

(13.4) __ no values are missing 13.4 to median ________JUL 15.9 _____ 18.6, 18.9 to 19.2, 19.5, 19.6, 19.7 (19.8)

(12.9) __ 13.1, 13.2, 13.4 _____________________________ AUG 15.6 ____ 17.9, 18.4, 18.5, 18.8, 18.9 (19.1)

(10.5) __ 10.8, 10.9 ___________________________________ SEP 13.3 ____ 15.5, 15.8, 15.9, 16.2, 16.4, 16.5, 16.7 (16.8)

(5.3) ___ 5.4 to 6.3, 6.6, 6.7, 6.8 ______________________ OCT  9.7 _____ 11.6, 12.1 (13.1)

(2.3) ___ 2.4 to 2.7, 3.8 _______________________________ NOV 6.1 _____ 8.8, 9.0, 9.6 to 9.8 (9.9)

(-0.8) ___ -0.6, -0.4, -0.1, 0.0, 0.2, 0.8, 0.9 _____________ DEC 4.2 ______ 7.0, 7.1, 7.8, 8.0, 8.2 to 9.5 (9.6) 

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Which of these is now closest to a median value? These are the ranks that the least extreme missing values would take in 2023 (or Nov-Dec 2022) if they occur. They would remain potentially at the same rank in later years, if no values more extreme (whether recorded before or not) happened -- if so, these ranks would drift one closer to the median and become that much more noteworthy. I have listed these in order rather than chronologically.

Coldest missing value closest to median _________ Warmest missing value closest to median

FEB 1.3 would be 31st coldest ____________________ OCT 11.6 would be 28th warmest.

NOV 3.8 would be 20th coldest ___________________ MAY 13.2 would be 20th warmest.

JAN -0.5 would be 17th coldest. ___________________ JUN 16.3 would be 15th warmest.

DEC 0.9 would be 17th coldest ____________________ DEC 7.0 would be 15th warmest. 

APR 5.6 would be 16th coldest ____________________ AUG 17.9 would be 11th warmest.

MAR 2.6 would be 12th coldest ___________________ SEP 15.5 would be 11th warmest. 

SEP 10.9 would be 7th coldest ____________________ NOV 8.8 would be 10th warmest. 

OCT 6.8 would be 6th coldest _____________________APR 10.4 would be 6th warmest.

AUG 13.4 would be 5th coldest ___________________ JUL 18.6 would be 6th warmest.

JUN 11.7 would be 2nd coldest ___________________ JAN 7.2 would be 4th warmest.  

MAY 8.4 would be coldest ________________________ MAR 8.4 would be 4th warmest.

JUL 13.3 would be coldest _________________________FEB 7.4 would be 3rd warmest.

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So while no v2.0 missing values are comparable to the old 5.9 December mark, the most impressive missing warm month now is 11.6 for October which would only rank 28th warmest.

While a 1.3 Feb would be 31st coldest, it seems less likely to occur before an 11.6 October because the median is nowadays close to 5.0 for February rather than 4.0 long-term. And the median for October is not much below the missing 11.6 in recent decades. 

Anyway, for those lamenting the loss of the 5.9 December search, I think an 11.6 October is about the same kind of quest given the trends, and a 13.2 May is almost as easy to fill in.

I don't really think we'll be seeing any of the missing cold values filled in, or perhaps one or two in a century, although we have seen two colder Decembers since 1981 than the 0.9 that is 17th coldest, and March 2013 just about removed that gap of 2.6 (it has been revised to 2.8 in v2.0).