"Scott W" wrote in message
...
On Thursday, December 11, 2014 12:06:40 AM UTC, Bernard Burton wrote:
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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Thanks Bernard. The Excel link is http://1drv.ms/1ByrMYC
It is possible that my figures are skewed in favour of cold ie Luke
Howard's records 1806-1831? Another possible discrepancy is that I use
Paul Bartlett's average of -0.7C to +0.7C when compiling these tables.
Best regards, Scott
Further to this thread:
I have analysed the monthly mean temperature anomaly for each Jan, Feb and
Mar from 1882 to 2011 in the Wokingham series data, and ranked them into
categories, Mild or very mild = anom +1, Normal = anom +1 to -1, and cold
or very cold, anom -1. I have assumed that the years selected as having 38
minus Decembers at Greenwich will be applicable to Wokingham.
For the years meeting the 38 minus rule in December as shown in the link to
Scott's blog, in January there are 10.0% of all years in the cold/very cold
category, in Feb there are 7.7% in that category, and in March, also 7.7 %.
For other cold/very cold cases, in Jan 20.0% did not satisfy the 30 minus
rule, Feb 19.2% and Mar also 19.2%.
For the years satisfying the 38 minus rule, the ratio of cold/very cold to
normal, warm or very warm is : Jan 48:52, Feb and Mar 37:63.
So, twice as many cold or very cold Januarys are not preceded by a 38 minus
rule Dec as are preceded by one, and 2.5 times likewise for both Feb and
Mar.
If a forecast of a cold or very cold January was based on the 38 minus rule,
it would be correct on 48% of occasions. For both February and March this
would drop to 37%.
So as a predictive rule it doesn't have a lot going for it, IMHO.
--
Bernard Burton
Wokingham Berkshire.
Weather data and satellite images at:
http://www.woksat.info/wwp.html
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