"A fine soft day" would normally mean it was raining, but not hard enough to keep indoors, if you had some reason to be out of doors. It sums up a cheerful attitude in the face of adversity. So it's also used as a joke when its raining cats and dogs.

"A fine moist day" I've also heard sometimes, meaning a litle bit wetter than that.

The poem/song is included in a fine anthology called "Rich and Rare", edited by Sean MacMahon in 1984. (He has four drips in the last line first verse as well as in the second, which sounds more likely to me.)

The book has a potted biography of the writer: Winifred Letts was born in Dublin in 1882, educated at Alexandra College, and practised as a masseuse. She contributed several plays to the early Abbey repertoire, notably "The Challenge" (1909) and wrote reminiscences about life in Leinster called "Knockmaroon" (1933). She married WHF Verschoyle. She is mainlt remembered today for her lyric "A Soft Day" which was printed in her first collection of poetry, "Songs from Leinster". She died in 1950.

But let's have that Letts poem about Stephen's Green as well, Sarah. There's a lovely little poem about Stephen's Green which I can't lay my hands on, but I think it's by Patrick Kearney who wrote The Soldier's Song - about being born in the heart of the city, but there's fairyland on the doorstep, in Stephen's Green.