ominous

“Ill omens”

“Ill predictions”

“{'source': 'P.B.Shelley', 'text': 'my words with inauspicious thunderings shook heaven'}”

“A dead and ominous silence prevailed”

“A by-election at a time highly unpropitious for the Government”

“A baleful look”

“Forbidding thunderclouds”

“His tone became menacing”

“Ominous rumblings of discontent”

“Sinister storm clouds”