On Tuesday, December 17, 2013 4:01:11 PM UTC, Scott W wrote:
On Tuesday, December 17, 2013 11:21:39 AM UTC, Norman wrote:

Norman wrote: Scott W wrote: Of interest to contributors in the Home Counties I have published a snow survey / winter index on my blog for my area in east London. It is inspired by the old Snow Survey of Great Britain which ceased publication after the 1991/92 season. Further to Dave Cornwell's comment a few weeks back that people mostly remember a winter through the amount of days with snow lying I decided to use the data I produced for my winter forecast and try to find out what snow cover has been like in my area going back to 1946/47 - the first year of the original snow survey. I then divided the snow lying days by the winter mean to give the index. I realise there is the work of Bonacina to consider but as this is national I wanted to look more indepth Not surprisingly the 62/63 season came out a long way ahead of the rest - mostly through the sheer sustained depth of the cold. There's also one or two surprises - strange how the memory can fool you. It is a work in progress and I would welcome any input. http://wp.me/p2VSmb-8M Using the mean temp in deg C gives a highly non-linear index as the temp approaches 0 deg C. For example, for the same snow depth the index calculated with a mean temp of +0.1 is double the index calculated with a mean temp of +0.2 deg C, which is certainly not the sort of result you are looking for. A mean temp of 0 deg C would give an index of infinity then as mean temps dropped below 0 deg C the index would be a decreasing negative value. Using a mean temp in deg K would be a much more valid approach. Sorry, I meant "for the same number of snow-lying days" not the "same snow depth". To illustrate the non-validity of using temps in deg C, if you carry out an identical exercise using temps in deg F instead, the relative severity of the individual winters changes markedly. Neither method is valid. The only valid way is to use deg K. -- Norman Lynagh Tideswell, Derbyshire 303m a.s.l.



Thanks, Norman. the degK approach makes complete sense - I'll address the necessary changes on the spreadsheet when I get a moment. As for the snow 'cm days' it is looking increasingly like I'll need a trip to Exeter to view daily data - apart from my own relatively limited stats I only have access to the monthly data in the Snow Survey. All fascinating stuff
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What chance of winter mean temp going below zero C in Wanstead?
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Zero if you ask me.
If you are worried I would use Fahrenheit rather than Kelvin.
The latter scale would make the index rather insensitive.
People in the past have always had to use multiplying/dividing factors to make their indices show what they are trying to show.
The length of the snow lying is important but makes the working out of an index rather sklushy.

Speshially over a glass of mulled wine.

Len
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Len