While in Scandinavian countries are frosts in late spring and early autumn relatively usual, in mid-latitudes it is very rare to have so cold mornings in so late season.
In last 3 mornings, cold temperatures again hit large parts of Europe /after cold finish of the last workweek: https://mkweather.com/cold-mornings-until-28-may-in-british-islands-early-june-2021//.
The coldest was in the UK and the Spain, where frosts in lower situated basins appeared.
On Saturday, 22. May 2021, the coldest national TOP temperatures were measured in Cairnwell, the UK, -3,3°C, Miercurea Ciuc, Romania and Berovo, North Macedonia, +0,3°C, Gurteen, Ireland, +2,0°C, Florina, Greece, +2,2°C, Kolka, Latvia, +2,2°C, Wasserkuppe, Germany, +2,3°C and Viljandi, Estonia, +2,4°C (*little mistake in map below).
On Sunday, 23. May 2021, the coldest temperatures were measured in Altnaharra, the UK, -3,2°C, Nesteres, the Spain, -0,5°C, Mende, France, +1,2°C, Telgárt, Slovakia, +1,7°C, Pec pod Sněžkou, Czechia, +1,9°C, Cewice, Poland, +2,7°C and Nigula, Estonia, +3,0°C.
On Monday, 24. May 2021, the coldest morning was measured in Cairnwell, the UK, -0,8°C, Mariazell, Austria, 0,0°C, Telgárt, Slovakia, +1,3°C, Bamberg, Germany, +1,4°C, Dublin, Ireland, +1,4°C, Pec pod Sněžkou, +1,6°C, Horsens, Denmark, +2,3°C and Zakopane, Poland, +2,6°C.
According to the newest GFS forecast, ground frosts will be still possible in mid-latitudes of Europe until the end of May 2021, although regional impact and intensity of ground frosts will be weakening.
Widespread ground frosts are still forecasted in next 3 mornings (25.-27. May 2021), then it will be only a concern of little selected European regions.
Source: meteologix.com
Source: wetterzentrale.de
