It is grammatically correct and usable in written English.
For example, you could use it in a sentence such as: "The lion roared loudly when the rabbit came too close to its den."
The mob roared loudly, and there seemed a near-unanimous recommendation.
The trembling of his hands and the motor roaring loudly in the back of his skull had enlightened him.
At one point Prince asked the crowd: "You all still read books right?" The audience roared loudly.
Our long green line snaked closer to the aircraft, the engines roaring loudly, drowning out everything except for the sound of my own thoughts.
But these weary beasts, rather than slipping quietly into extinction, are still roaring loudly and trampling a lot of real estate, even as the swift new creatures that are supposed to kill them off evolve and proliferate with startling rapidity.
But when Boston's loss was posted on the Yankee Stadium scoreboard at 10 37 p.m., the fans -- who had been so animated during the pregame ceremony -- realized the Yankees had just clinched the American League East, and they roared loudly as the Yankees batted against Tampa Bay in the bottom of the seventh inning.
In passing maneuvers on two-lane roads, the V-8 roars loudly and gives you the kind of confident acceleration you would expect from an eight-cylinder, $40,000-or-more luxury car.
In the meantime, the crowd roared loudly, heckling Egar and supporting the beleaguered bowler.
Katy Perry is roaring loudly on top of Forbes' 2015 list of the highest earning women in music.
I roared loudly at everyone and began cackling to myself after each drink, swearing merrily all the while.
