Discussion on AASC list  involving "The Origins of the '30-year Normal'"  
on 13-14 Dec 2012
 From: Glen Conner   
 Ken was much too modest about his involvement with the development of the AASC statement on normals. It was at the AASC meeting on Mt Hood in Oregon that the normals discussion occurred. That meeting opened with Ken Kunkel presenting the problem of normals. It was a timely presentation because the decadal normal calculations were just two years away and the 'hot" topic in the media was global warming.  That discussion was one of the most interesting and productive that I remember from our annual meetings. There is this in the minutes of that meeting:
"The statement on normals presented at the meeting by Ken Kunkel be re-drafted in light of comments made here today and be given for publication in The State Climatologist, that comments be invited until the 1st of February, and that we seek dissemination in an AMS publication."
Ken and Arnold Court composed the draft.

Ken sent out the redrafted statement to the SC's and asked for comments by 15 February 1988. At the AASC meeting in Bar Harbor ME in 1889, Ken presented the final statement as the first speaker at that meeting. There were no objections and  Ken submitted it to the BAMS.

So far as I know, it still stands as the AASC statement on the matter.
Glen

I can't remember Arnold without remembering him jokingly telling me at the AASC meeting in Charleston SC that he had written a new book, "The Perfect Climate, And Why We Don't Want It To Change."

 From: Kenneth Kunkel   
Nolan and others,

It appears you have gotten all of the info you need. However, the attached document has a bit of historical information, and I can attest it is directly from the mouth of Arnold Court.

Ken
Attached document was 
 Kunkel, K.E.  and A. Court,  1990:  Climatic means and normals-A statemenf of the American Association of State Climatologists  (AASC).  Bull. Amer. Meteor. Soc., 71, 201-204. 

From: Ned Guttman   
Marina,

30 years is anything but optimal for prediction. One of the earliest studies was a 5 part series done I think in 1957. I can't remember the author, but I think it was Arnold Court.  Five to 7 years is good for temperature, 50+ for precip.

Describing climate in terms of what has happened, however is a different story. The "basic statistics" refer mainly to independent data, and the data we are dealing with is rarely independent.

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 From: Xiaomao Lin   
Hi All:  I am not sure if the Russia climate scientist Bruckner is the information. It seems that initially it was 35 yrs (like 1881 to 1915 used) because of 35 cycles in some Russian lakes. Then it changed into 30 yrs for easy computation.  Thanks.  Xiaomao Lin
[EJH Insert here:
http://en.wikipedia.org/wiki/Eduard_Bruckner
http://todayinsci.com/B/Bruckner_Eduard/BrucknerEduard-Quotations.htm -- interesting quotes on natural and human induced climate change from 
http://stevengoddard.wordpress.com/2012/06/06/1904-bruckners-law/ -- contains a newspaper item from Argus, Jan 1904.
Bruckner, E. :  1915 The settlement of the United States as controlled by climate and climate oscillations, in Memorial Volume of Transcontinental Excursion of 1912 of the American Geographical Society of New York.  125-139. 
http://archive.org/stream/memorialvolumeof02amer#page/n21/mode/2up 
]
 From: Marina Timofeyeva   
All,

I always got in terms with using 30-years only for computation of normals, thinking that Basics of Statistics define a sample of 30 as the one that allows estimation of robust statistics using traditional methods. For sample less than 30 members, defined as small sample size, there are some special statistical techniques recommended. Although I do not see this referenced in the resources you provided, I hope this was the rationale for using the 30 years.

Thanks, Marina
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 From: DeWayne Cecil - NOAA Affiliate   
All,

Here is what NCDC has for "Normals", probably more than you ever wanted to know!  http://www.ncdc.noaa.gov/oa/climate/normals/usnormals.html#WHATARENORMALS
DeWayne
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From  Chris Fiebrich  
Nolan,

I came across the "history of normals" a while back in the WMO Guide to Climatological Practices:
http://www.wmo.int/pages/prog/wcp/documents/Guide2.pdf
In Section 4.8 Normals:
Historical practices regarding climate normals (as described in previous editions of this Guide [WMO‐No. 100], Technical Regulations [WMO‐No. 49]) and WMO/TD‐No. 1188) date from the first half of the 20th century. The general recommendation was to use 30‐year periods of reference. The 30‐year period of reference was set as a standard mainly because only 30 years of data were available for summarization when the recommendation was first made. The early intent of normals was to allow comparison among observations from around the world. The use of normals as predictors slowly gained momentum over the course of the 20th century.
Later in that section, it states:
A number of studies have found that 30 years is not generally the optimal averaging period for normals used for prediction. The optimal period for temperatures is often substantially shorter than 30 years, but the optimal period for precipitation is often substantially greater than 30 years. WMO/TD‐No. 1377 and other references at the end of this chapter provide much detail on the predictive use of normals of several elements.
Interesting to know the history!
Chris
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From: Kelly Redmond 
Nolan,

Am in DC right now, visiting NOAA HQ, so don't have good
access to my own system, but there were a lot of reasonable
reasons why we settled on 30 years for "normals."  I've always
thought the documentation of this decision was very good.
and, for the circumstances, 30 years was indeed the best
compromise.  Will see if I can find some of this when I get
back to Reno.  This was not arbitrary, but actually a
well-thought-out compromise among many factors.

The odd thing is that this is about the career life of a
practicing climatologist before they go insane.

Kelly
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 From: Antony R. Bergantino   
Some info in WMO's "The Role of Climatological Normals in a Changing Climate"
http://www.wmo.int/pages/prog/wcp/wcdmp/documents/WCDMPNo61.pdf
3. The historical development of the concept of climatological normals
The concept of the 30-year climatological standard normal dates from 1935, when the Warsaw conference of the International Meteorological Committee recommended that the period 1901-1930 be used as a world-wide standard for the calculation of normals. In 1956, WMO recommended the use of the most recent available period of 30 years, ending in the most recent year ending with the digit 0 (which at that time meant 1921-1950). This decision was guided, at least in part, by increased knowledge of long-term climatic fluctuations, although a 1967 report by a working group of the Commission for Climatology (Jagannathan et al., 1967) still took the view that:
“For the most part, large-scale climatic fluctuations consist of non-linear variations that oscillate in an irregular long-period manner rounda long-term climatological average."
Despite the 1956 WMO recommendation, the Technical Regulations continue to define a climatological standard normal as per section 2 above.
Note: the Standard Normal reference in section 2 is of a sequence of 30-year periods (1901-1930, 1931-1960 etc)
--Tony
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From: Phillip.Pasteris@ch2m.com 
Nolan,

This is a good starting point.  Copy of Ned's publication (see below) attached.
http://www.ncdc.noaa.gov/oa/climate/normals/usnormalshist.html

I guess he needs to write something about "the new normal" that is making the rounds now.  He might be too busy in retirement?

Phil
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 From: Ned Guttman   
   Nolan,
Here's a reference. Section 2 gives the background. Google the title - it's available online from AMS.
Guttman, N.B., 1989:  Statistical descriptors of climate.  Bull. Amer. Meteor. Soc., 70, 602-607
Happy holidays,
-- 
Ned Guttman
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 From: nolan@engr.colostate.edu   
Dear AASC wizards and historians

Would someone please refresh my memory regarding the origins of the
30-year "normal" and any references that support that.  I recall seeing
1891-1920 averages in an early USWB document, but I don't recall them
being referred to as "normals" until quite a few years later.  By
1931-1960 they were called "normals"

Thanks for the help.

Nolan
Colorado
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