The phrase "threatening to rain" is correct and usable in written English.
You would generally use it when talking about the weather. An example sentence would be: "The sky is grey and threatening to rain."
With the sky threatening to rain a few weeks ago, patrons trickled into Freddy's Bar for their pick-me-ups.
Now that the date has finally arrived … and a Nor'easter has settled over Gotham, threatening to rain on a season-long parade.
If you stand under the High Line itself, the unused 1.45-mile viaduct built almost 70 years ago by the New York Central through the far West Side of Manhattan, it looks like a hazard, threatening to rain concrete chunks, steel plates and pigeon droppings down on the street.
But this year, when it's always raining, about to rain, threatening to rain or just having stopped raining, he's the most important guy in town, with the almost full-time job of sprinkling 50-pound bags of Turface Allsport Pro, a clay-mix drying agent, onto soggy infields and pitcher's mounds.
Add in aggressive apocalyptic ideas that suggest time is running out and quick action mandatory and you have a perfect storm of mobilized resentment threatening to rain bigotry and violence across the United States.
Who could forget the way he stoked the already glowing embers of the Korean crisis in August by threatening to rain "fire and fury like the world has never seen" ― an obvious nuclear reference ― on North Korea?
The damp woods smell earthy and musky, and it threatens to rain during our visit.
It threatened to rain throughout Saturday's qualifying session, on a cold, blustery, overcast afternoon.
And it came after a tempestuous few weeks, in which North Korea threatened to rain nuclear missiles on both South Korea and the United States.
It's about demonstrating that there are limits to what other governments can choose to do without repercussions, and maintaining our credibility when we threaten to rain those repercussions down.
And it does not go unnoticed on Arab television screens that Palestinian demonstrators have started waving Iraqi flags, just as they did when Mr Hussein threatened to rain scuds on Israel during the Gulf war.
