Driest April for years followed by the wettest May

No Irish observations south of the border because I haven’t added their LTA data to my application yet

You would have thought that May 2021 is heading for the record books with the amount of rain we’ve seen so far this month. The only places below average this month are Aultbea, Wick and Kirkwall, the rest of the UK is in a range 150% to 300% of the LTA. The wettest May in the UK in the gridded data series since 1862 was the May of 1967. The total was 191% of the LTA, so it looks from the percentages DFA we have with a week still to go that May 2021 will be crowned wettest on record. That’s probably not going to be the case regionally especially in the north and west of Scotland where 2011 was also very wet.

Raw data (and map) courtesy UKMO

Bala highest DFA of 400%

I notice that Helen Willetts mention that Bala has had over three times it’s normal rainfall this May in her Countryfile weather forecast. This percentage will be based on the total for the whole month. I do it slightly differently a kind of pro rata method. I’ll show you want I mean. The May long term average for rainfall at Bala is 72.8 mm according to DataPoint. Therefore by the 24th Bala should have received 56.4 mm, in actual fact Bala has collected 225.8 mm (06-06), which makes the percentage difference from average using this method ~400%. Bala might have the highest DFA but Capel Curig, as is the case so often, is the wettest place so far this month with 254 mm of rain. Aren’t climate statistics just wonderful.

YNOP data courtesy of OGIMET

4 thoughts on “Driest April for years followed by the wettest May”

  1. It is certainly the case as of today (25th) here in Wembury, SW Devon.
    April was the driest in my record since 1985 with 5.5 mm.
    May is now my wettest with 137.9 mm.
    All measurements in standard 5 inch copper gauge. Elevation 83 m asl.

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