Question:
How clear does the moon need to be to say kiddush levana? For example, is it clear enough if it’s fuzzy because it’s behind a thing cloud.
Answer:
This is a common issue. The rule is that we can say kiddush levana if the moon is giving enough light to us that (if we would be in an area without street lights) we would be able to benefit from it. If we can see the shine of the moon on the ground, that is shows that the moon it is bright enough to say the bracha. Therefore it would depend on how big the moon is, together with the thickness of the clouds or fog.
Best wishes
Sources:
O:CH 426-1 M:B 426-3.
