Ways to express "something bad is going to happen"

Solution 1:

Here are some suggestions for informal asides:

• "I have a bad feeling about this..."
• "Nothing good can come of this."
• "The s**t's about to hit the fan." (colloquial, and offensive to some)
• "You think this is bad, wait 'til you see what's about to happen." (when the situation is already discernably "bad")
• "Well, that's thrown a spanner in the works." (BritE, and said after observing the precipitating event)
• "Uh-oh."

If you're asking about how to notify a superior of an impending system failure or political snafu, you could try:

• "(Sir/Mr...insert title here), there's no good way to say this, but... [brief statement of the impending consequences of the failure]. But I think I have a way to (avert/mitigate/contain the damage)/(correct the problem)." (Explanation of what happened to follow upon request.) Do your best to bring at least one proposed solution when reporting the problem, and ideally bring a small party of experts with you.

I had to read quite a bit into your question; I trust some of this will be helpful.

Solution 2:

"something bad is going to happen"

=

There was a sense of foreboding.

Edit:

For example, before he was assassinated, Martin Luther King, Jr., felt a sense of foreboding.