December 2010

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darrog
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Re: December 2010

Post by darrog » Mon Jan 03, 2011 9:08 pm

Mean temps' you would think it was simple - AND IT IS:

WL worked out my yearly mean temp as .........7.4c
This it rounded up from................................7.39c

I have now worked out my yearly mean temp based on the 'Old way' (min+Max divide by 2)

and the yearly mean temp' is.........................7.39275c

Spot the difference!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Yes when a monthly mean can be 1.99c instead of 2.1c you would want to use the lower figure, and in December I would have liked -2.0c instead of -1.6c - but certainly my figures for this year have made diddly squat difference.

Also if you think of it this way, eg: max' =10c - Min =0c, but the min' was only reached for 5 mins in 24 hrs, but the max' was held for 2+ hrs and all the 'old way' is giving you is a mean based on two set points in a 24hr day and not a true reflection of the entire 24hr period.
Darren Rogers - he who submits the most interesting posts, AKA Mr Data
Maulds Meaburn

Anne
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Re: December 2010

Post by Anne » Mon Jan 03, 2011 11:17 pm

Oh, well ..... good then! I can go back through all my old books and calculate a Mean temp. I really thought the official records would be mor complicated than that!

Erm ......... 24 years ....... I may be some time ;)

Anne

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embayweather
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Re: December 2010

Post by embayweather » Tue Jan 04, 2011 1:51 am

Please find the details for Bolton le Sands. like the rest a record breaking month, The driest December on record, the coldest temperature ever recorded here (since 1992) and the month with the least wind on our records , ie 20+ calm days!!

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Paul C
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Re: December 2010

Post by Paul C » Tue Jan 04, 2011 11:03 am

darrog wrote:Mean temps' you would think it was simple - AND IT IS:

.
There is a weather means rule somewhere

"Means Table Rule

If the mean temp Mean Max or the Mean Min comes to for eg 15.35 it is rounded off to the even number so in this case it would be 15.3 but if the figure was 15.45 it would be rounded off to be one higher 15.5.

EG
15.05 change 15.1
15.15 leave at 15.1
15.25 change to 15.3
15.35 leave at 15.3
15.45 change to 15.5
15.55 leave at 15.5
15.65 change to 15.7
15.75 leave at 15.7
15.85 change to 15.9
15.95 leave at 15.9
16.05 change to 16.1

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darrog
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Re: December 2010

Post by darrog » Tue Jan 04, 2011 11:13 am

Paul,

thanks - useful.

What are your thoughts on what mean temp to use - the one provided by WL or having used the VPro2 daily min/max to add together and divide by 2?
Darren Rogers - he who submits the most interesting posts, AKA Mr Data
Maulds Meaburn

Anne
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Re: December 2010

Post by Anne » Tue Jan 04, 2011 2:04 pm

I'm thinking again about this! Surely you can't just take the month's maximum and the month's minimum, add them and divide by two. This would surely give a very odd result, which was not really meaningful, if there had been some extremes of temperature? ie: the max and min may be in no way representing the whole month.

This is why I have never done a monthly mean .... well, I guess I was just too lazy to do all those sums! I just did a mean Maximum for each month. (ie: add all the days together and divide by 30 or 31)

Anne

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Re: December 2010

Post by Andy Woodcock » Tue Jan 04, 2011 3:31 pm

Anne wrote:I'm thinking again about this! Surely you can't just take the month's maximum and the month's minimum, add them and divide by two. This would surely give a very odd result, which was not really meaningful, if there had been some extremes of temperature? ie: the max and min may be in no way representing the whole month.

This is why I have never done a monthly mean .... well, I guess I was just too lazy to do all those sums! I just did a mean Maximum for each month. (ie: add all the days together and divide by 30 or 31)

Anne
Hi Anne,

No, its the Average Daily Max and Average Daily Min that you take and divide by 2 (not the absolute Max and Min!)

Thats how the MetO do it and if we want to compare data then we need to do the same.

Cheers,

Andy

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Re: December 2010

Post by Anne » Wed Jan 05, 2011 1:13 pm

Ah! Right ... thanks Andy - maths never my strong point!!! :oops:

Anne

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darrog
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Re: December 2010

Post by darrog » Fri Jan 07, 2011 11:58 am

Just looked at the Met'O figures for December and it gives the following figures for NW england and wales:

Mean Max' = 2.5c
Mean Min' = -4.3c

so what should the MEAN equal?
You would think = -0.9c

And you would be wrong.

MEAN quoted = -1.0c

simples.
Darren Rogers - he who submits the most interesting posts, AKA Mr Data
Maulds Meaburn

Anne
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Re: December 2010

Post by Anne » Fri Jan 07, 2011 4:29 pm

Hmmmmmm! :? :lol:
Anne

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