You will meet all of the module's navigational objectives even if
there are clouds. We will practice indoors with the
mechanics of using a sextant, and work on exercises to gain
experience in plotting positions from the various sorts of sights,
star, planet, moon, or sun.
The main difference is that we will have more FUN if the skies
are clear. So pray for good weather!
The exam module is primarily a classroom exercise anyway, so bad
weather is a non-issue. You will meet all of the module
objectives even if the weather is miserable.