• Blog home
  • Elections
  • Polling
  • Sport
  • Weather
  • Forecasting
  • Diversity
  • Stats Training
  • Misc
  • Archive
  • Twitter
  • Back to Marriott Statistical Consulting

Nigel Marriott's Blog

An independent statistician using data to understand our world and to predict the future

You are here: Home / Archive / UK Weather Trends #3 – Autumn 2017

UK Weather Trends #3 – Autumn 2017

December 16, 2017 By Nigel

Meteoologists define autumn in the UK to be the period from September to November so autumn is now over and we are officially in winter.  The 2017 autumn was completely unremarkable but this hides the fact that our autumnal climate has changed quite notably over the last 25 years.

I analyse the long term trends in the UK weather using a statistical tool known as STANDARDISATION.  This means that the 3 key variables of Temperature, Sunshine and Rainfall are recalculated so that they all have the same units, which is number of standard deviations from the mean.  Such variables are known as Z-SCORES.  For more information on how I have done this, please read my post on trends in the UK summer.

The Z-Scores for Temperature, Sunshine and Rainfall are shown in the 3 charts below.  Each chart also contains an 11-year centred moving average which gives an idea of the underlying trend.

Standardised variables aid interpretation of data in many ways.  If the standardised value is positive, it means that the value is above your average or expected value.  If it is negative, then the value is below your expected value.  If the original variable is approximately normal in its distribution then the vertical scale gives us an idea of how typical or atypical each year is.  Z-Scores in the range -1 to +1 are considered typical values and completely unremarkable.  Z-scores in the ranges -2 to -1 and +1 to +2 are considered to be uncommon values but still entirely plausible and such values should not cause us concern.  When Z-Scores get into the ranges -3 to -2 and +2 to +3, we should start paying closer attention and asking ourselves if something has changed especially if we get a sequence of successive points in these ranges.  Finally, if the Z-scores are less than -3 or greater than +3, that is normally regarded as a clear call to action.  There are in fact many ways of interpreting Z-Scores and what I have said so far merely a gives an overview of the most basic interpretations.  A whole field of study known as Statistical Process Control (SPC) is dedicated to building and interpreting such charts (known as a CONTROL CHART).

For the autumn of 2017, the z-scores for temperature, sunshine and rainfall were respectively +0.6, -0.7 and 0.  Officially this means autumn was warmer and darker than normal with normal rainfall but the magnitude of the z-scores clearly point to an entirely unremarkable autumn.  If you have been following my monthly weather tracker then this should be no surprise as all 3 months stayed pretty close to normal.

Since the 3 moving averages in the above 3 charts all use the same units, they can be plotted onto the same chart as below.

This clearly shows a shift in our autumnal climate over the last 100 years of almost 1 standard deviation.  Recall that the baseline for the z-score calculation is based on the idea of “living memory” which I have defined to be the last 50 years of 1967 to 2016.   We can characterise our autumns broadly as follows:

  • 1915-1925 – we had cold dry autumns.
  • 1935-1975 – we had stable autumns which were on the cool, dull and dry side.
  • 1975-1995 – similar to the previous period of 1935-75 but with a brief spell in the early 80’s when we had wet autumns.
  • 1995-today – a clear shift in our climate occurred and we now have warm, bright and wet autumns.

So when I said that 2017 was unremarkable, in fact it was unremarkable only in the context of living memory.  Compared to the 1940s, 2017 was actually warm, bright and wet.

A further point may be apparent from the above chart.  The z-scores for temperature, sunshine and rainfall all appear to be correlated.  In fact this is somewhat illusory as the above chart uses moving averages.  If we look at the actual z-scores, we can see in the 3 scatter plots below that there is only a limited correlation between the 3 variables.

The brown square in each chart is 2017.  In all 3 cases, the charts reinforce the ordinariness of 2017.  However, scatter plots can be useful to identify unusual years that do not follow the normal relationships.  They can also be used to identify the true dimensionality of our weather, a concept I will explore in my next post on UK winter weather trends.

Filed Under: Archive Tagged With: multivariate data, Presenting data, standardisation, trend analysis, Weather, weather trends, z-scores

Search this site

More blogs

Pay Gap Data #6 – Where can I find gender pay gap data for 2022?

This post was updated on 27th March 2023 with the latest data The government requires all … [Read More...] about Pay Gap Data #6 – Where can I find gender pay gap data for 2022?

6 Nations History #3 – The men’s story so far in 2023

The 2023 Six Nations (Men's) ended with Ireland beating England to win their 3rd 6 Nations Grand … [Read More...] about 6 Nations History #3 – The men’s story so far in 2023

Pay Gap Case Study #7 – Does the Department for Work & Pensions have a Gender Pay Gap?

The Department for Work & Pensions (DWP) says for every £1 paid to the median man in March 2022, … [Read More...] about Pay Gap Case Study #7 – Does the Department for Work & Pensions have a Gender Pay Gap?

UK Weather Trends #24 – Winter 2023

Winter 2023 was the 10th sunniest on record but I doubt we may have noticed.  There are indications … [Read More...] about UK Weather Trends #24 – Winter 2023

UK Weather Tracker #73 – February 2023

It was the 7th warmest February on record in the UK whilst being dry and sunny. … [Read More...] about UK Weather Tracker #73 – February 2023

Subscribe to Our Newsletter

Join our newsletter mailing list

Receive latest news, articles and offers

Select the categories of interest:

We are GDPR compliant. Read our privacy and Cookie policy for more info.

Check your inbox or spam folder to confirm your subscription.

Copyright © 2023 ·Registered in England, Company No. 5577275, VAT No. 883304029. Registered Office – 65 Bristol Road, Keynsham, Bristol, BS31 1EG