Ominously means menacing. Here are some sentences.
The thunder rumbled ominously. He laughed ominously as he opened the door.
Although the weather was mild, dark clouds gathered ominously on the horizon.
The librarian glared ominously at me when I laughed out loud. The tornadic storm hovered ominously nearer and nearer, so I left.
an ominous bank of dark clouds Ominous means evil, and leads to ominously meaning evil. My source of helping you was dictionary.com glad I could help
The tree branch scratched at the little boy's window ominously, forcing him to pull the covers over his head and close his eyes in fear.
There is such a word as ominously but I couldn't find it in the thesaurus.On the other hand I found ominous and two synonyms are doomed and fearful.
As the moon rose luminously, a dark spectre rose ominously.
The ancient door creaked ominously as it slowly opened to reveal the neighbor's slobbering St. Bernard puppy dog, named Cujo.
It wasn't raining yet, but the storm-clouds towered over us ominously.
The crest of the wave towered ominously over our heads. We'll crest this hill, before long.
The sky roared with anger!
In the ordinary useage of the word "ominous", you could substitute it with its synonyms: fateful, sinister, threatening or menacing. Hope that helps.