expression, i-adjective
the clouds look menacing; threatening weather
Literal meaning: the sky looks threatening, suggesting bad weather is coming.
雲行きが怪しいから、傘を持って行ったほうがいいよ。
The clouds look menacing, so you'd better take an umbrella.
expression, i-adjective
things don't look good;
Idiomatic extension: the outlook for a situation is uncertain or threatening, not necessarily weather-related.
交渉は雲行きが怪しくなってきた。
The negotiations are starting to look ominous.