May 2019 set a new record though you might not have known as the month seemed unremarkable. In fact it was the most “average” May on record across all weather variables!
The meteorological year starts in December which is why December appears as the 1st data point in the charts below. More information on the layout of the charts can be found in this post. Points lying between the upper and lower deciles are shown as open black circles, points lying between the deciles and minimum/maximum are shown as solid black circles and any month with a new record is shown as solid black squares.
As I explained in October 2018, the addition of a Temperature Range chart (B) means I now have 7 charts to I update every month so I will rotate which 6 appear 
in the deck above and plot the 7th as a separate chart. I stated that Frost is of least interest in the summer months which means chart C above is for Sunshine and Frost in chart G here.
How Abnormal was May 2019?
I am introducing a new chart H which shows what I call the Abnormality Index. I began this post by saying that this month was the most “average” May on record and this is shown by the black square which is a new low. The closer to zero this index is, the less abnormal and thus more “average” a month is. The higher it is, the more abnormal the month is. When the index is over 100%, we can describe the month as unusual in some way.
The index is calculated using the 6 weather variables shown in the first graphic above. This means that Sunshine & Frost swap over in Winter and Summer. For each variable, I recalculate each month as a % on a scale from the median to the nearest decile. For example, there was 6.1 hours of sunshine in May which is closer to the median of 5.8 hours rather than the upper decile of 7.0 hours. Therefore, May 2019 was 22% along this scale. I repeat this process for the other 5 variables and I then take an average of the 6 percentages. For May, this turned out to be 14% and the 6 variables varied between 4% and 30%, indicating how all 6 were close to the median.
I intend to use this index going forward and it will be interested to see how it accords with my perceptions of the weather.
Regional Variations
May marks the end of the meteorological spring. I do not track regional statistics every month but I do track temperature by season for each region so 
I can update the regional temperature chart below. This shows the Z-Score for each region for the 2019 winter. A Z-Score is simply the regional temperature minus the long term average for that region divided by the long term standard deviation for that region. Doing this, gets around the issue that each region is different on average whereas z-scores all have the same scale, namely number of standard deviations from the mean.
For the UK as a whole, spring 2019 was above average in temperature in all regions.
PS: If you bookmark this link, it will be refreshed with the latest month’s data. I usually post the update in the first week of each month.
Click the relevant month to see my other weather trackers. Alternatively click the Weather Tracker hash tag below this post to see a list of all such posts.
- Click here for the latest month.
- 2019 – January, February, March, April, May, June, July, August, September, October, November, December
- 2018 – January, February, March, April, May, June, July, August, September, October, November, December
- 2017 – January, February, March, April, May, June, July, August, September, October, November, December
For analysis of trends by seasons, please click on the relevant season from this list or the Weather Trends hashtag below this post.
- 2019 – Winter, Spring, Summer, Autumn
- 2018 – Winter, Spring, Summer, Autumn
- 2017 – Winter, Spring, Summer, Autumn
