Nigel Marriott's Blog

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

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UK Weather Tracker #100 – May 2025

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The 2nd sunniest May on record in the UK follows the sunniest ever April & the 3rd sunniest March and resulted in the sunniest spring on record.  I am not surprised that in many regions it was also the warmest spring on record.

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 lower/upper deciles and the minimum/maximum respectively are shown as solid black circles and any month with a new record is shown as solid black squares.  All data is supplied by the Met Office and can be found here.

Every month I update 7 charts in all.  I rotate which 6 appear in the deck above and plot the 7th as a separate chart here.  Between March & October, Frost (chart G) is shown here since that is of least interest in these months.

How abnormal was May 2025?

Chart H displays my UK Weather Abnormality Index (see my May 2019 post for details).  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 abnormality index was 103% this month which is the 7th highest on record which clearly makes May 2025 an abnormal month.  This is the combined outcome of the 4th warmest, 2nd sunniest, 4th widest temperature range & 6th stormiest April on record.

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 here.

This shows the Z-Score for each region for the 2025 spring.  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 above or below the long term average.

The 2025 spring was the warmest & sunniest on record & this reflected in most regions.  Relative to their long term averages, Scotland & Northern Ireland were warmer than England and Wales.   For more details about the 2025 spring. click on the link provided in the list below.

 

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 what the weather was back then.  Months highlighted in bold had an abnormality index exceeding 100% indicating unusual weather.  Alternatively click the Weather Tracker hash tag below this post to see a list of all such posts.

For analysis of trends by seasons, please click on the relevant season from this list or the Weather Trends hashtag below this post.

For analysis of trends by year, please click on the relevant year from this list –

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