Like dark clouds
Else clues• Apocalyptic
• Appearing threatening
• Bad-looking
• Causing fear and anxiety
• Forbidding
• Foreboding
• Foreboding harm
• Inauspicious
• Lowering
• Menacing
• Portending harm
• Sinister
• Threatening
• Ultimately, radio operator jamming less dire (7)
• Worrisome