Mid-spring snow to very warm, from the E or SE

[Summer8906]

Also it looks like the weather was unsettled as well as warm, which meant it could well have felt oppressively muggy and humid. 21C with a fair amount of cloud, and rain around, probably would feel oppressive at this time of year. On the other hand 21C with clear blue skies and low humidity would not.

 

Edited April 28 by Summer8906

[Northernlights]

 Weather-history Yes sitting final Agri exams 8 floors up in Aberdeen on Ist June watching  dry snow showers coming in off the North Sea. Home to farm two weeks later  to baling hay at 28c and it never   really   cooled down till September.

[baddie]

March 2022 seen several days above 18c and wall-to-wall sunshine just after the equinox, then the last three days were dramatically colder and the 31st had snow showers on and off all day. Most extreme examples are the warm ends to March 2012 and 2021 followed by the cold and snowy starts to their respective Aprils

[B87]

 Summer8906 If it was muggy and cloudy then the minimum would be considerably warmer than 9c. 21c/9c in May sounds like it would be fairly clear.