Expectation: Call lightning helpfile suggests Call Lightning should work in cloudy/rainy weather: "The weather must be such that lighting can be called down from the skies. If there are no clouds or rain, then there will be no lightning." "Bolt from the Blue" edge also supports this, since it states that it gives the ability to call lightning out of a clear blue sky.

Reality: "The sky is cloudy and a cold northern gust blows." isn't "bad enough" for lightning.

Recommendation: Cloudy/rainy/lightning-y (and really, anything that isn't clear skies) should all be sufficient for call lightning. Restricting it more than that doesn't make sense, and doesn't fit the helpfile.