"clouds loomed" is correct and usable in written English.
You can use it to describe a dark, cloudy sky. For example, "As we drove through the countryside, dark clouds loomed ominously in the sky."
As spectators filed in, ominous clouds loomed over a portrait of Prefontaine on the field.
When the Yankees arrived at the ballpark Sunday afternoon, a tarp was smothering the infield as dark clouds loomed like overstuffed garbage bags.
Clouds loomed over Riverside Park in Manhattan the next day, but the stars were better aligned for the cast of this month's Hudson Warehouse production of "The Merry Wives of Windsor".
Storm clouds loomed overhead, and Clam Bar staff members busied themselves preparing for the Memorial Day rush, but none of that deterred Mr. Morrow, a retiree in khaki shorts, brown loafers, a sky-blue linen shirt and a baseball cap.
But then a dark bank of clouds loomed in the west, and a wind kicked in, adding to the destructive force of wave action and causing some waves to splash over the top of the new boards.
