The part of a sentence "was falling outside" is correct and usable in written English.
You can use it when describing a scene or action taking place outdoors. For example: "The leaves were falling outside, gently swaying in the autumn breeze."
One afternoon, snow was falling outside, and Jeb and I leaned forward and held our hands over the heat in this shelter we had built.
Out of a Circle The next day, snow was falling outside as some Otters gathered in a back corridor of the arena to play sewer ball before a game against the Niagara IceDogs.
No clone was falling outside the anammox cluster in the phylogenetic tree but sharing high similarity with Planctomycetes 16S rRNA sequences obtained with this pair of primer.
Throughout the party, snow is falling outside; by the end of the evening, snow blankets Ireland.
"There are certain drugs being used that are falling outside radar screens of labs," said Jim Gallagher, executive director of the task force.
The curtain rises on a prosperous late 19th-century Nuremberg household; it's a December evening, the snow is falling outside and the Stahlbaums are entertaining.
To re-read it is to experience the suddenness of snow falling; to re-read it as snow is falling outside is to find the mystery of the moment confirmed and deepened and enriched.
The majority of the displaced were falling outside the humanitarian net, he said.
The snow is falling outside my window, and the school is closed.
And despite the sunny positivism on the picture's surface, dusk is falling outside.
It is just before nine on a Friday morning in Edinburgh and a thin, faint rain is falling outside the Scottish Poetry Library in Crichton's Close, a short step from the tourist tat of the Royal Mile.
