According to what the internet tells me, this day is celebrated by American and Swiss citizens (though I don't know how true that is), to mark the changing of seasons. Of course, this only applies to the Northern hemisphere, where Winter is becoming Spring.
I chose this holiday today because it involves setting fire to frozen water. This reminded me immediately of a certain Russian we all know and love. The one who was 'the first lieutenant in the Russian Navy to set fire to an igloo'.