Cold Arctic air from Scandinavia deep into the European territory of Russia.
The strengthening of cold and clear skies contribute to intense night air cooling, increasing the likelihood of frost.
On the night of May 25, in some places in the ‘Yaroslavl’ and ‘Kostroma’ regions the temperature dropped to -1 ..- 2°C.
Such late May frosts in the regions of the Middle Strip are not rare, but dangerous, since they can damage already planted vegetable seedlings.
Thanks to Martin Siebert for this link