Warning siren for June went off on last monday of May

[judderbar]

I was wondering about the logic of the description that the warning siren goes off on the first monday of the month. When in fact it apparently does not go off on the first monday of the month.

The Siren for June went off on the last monday in May and there was no siren for the first monday of June which was the 7th of June

Is this a nordic thing? Or am i missing a few brain cells?