That’s a really great question- thanks for bringing it up!
In regards to working Full Moon Magick when the moon isn’t visible, I personally believe that when the moon is full the whole sky carries its energy and thus, it’s possible to work Full Moon magick even on cloudy nights . However, others may have differing opinions depending on the situation, so feel free to check out this topic (Opinions on the Moon) where different situations are explored.
As for drawing on the full moon on other nights, I wrote a bit about this in another thread, so I’ll refer to it here:
Taking a look at the Moongiant page for today (August 24), the moon is still at 95% illumination. Tomorrow it will be 90%, and the following day it drops to 83%.
The exact point of cut-off (when you feel you can no longer draw on the Full Moon Energy) will vary from one person to another. I personally consider the night before and after the full moon to still be full in regards to spellwork
Hopefully some of this info helps you to make your decision! No matter when you choose to cast you spell, wishing you a blessed time and successful casting
To answer your question about waiting for a better sky: It doesn’t matter if it’s cloudy outside.
Moonlight is as powerful as sunlight (it’s the same light) and its energy will reach you without any problem. Also, you never know if tomorrow it’s going to be cloudy or not, the best time to cast a spell is now!
Adding to what Bry said, look up and use your intuition. Sometimes we can still see the Moon through the clouds, or feel it even if we only get a glimpse. If you feel “Full Moon” energy, then that’s your answer!
Adding a little to this topic, this are the days; or nights, in which visualization comes in handy. Is cloudy, no problem. You can visualize the moon on your mind, if is difficult to do so, you can even use a on screen picture of the moon on your computer or phone, so you can focus to it. This can be done to other things also.
In certain rituals, what I do is to visualize myself using a robe. I mean I could use a robe, but the heat of the room, using a ceiling fan on, or without it so my incense and candles can be used, not that good right? I might be on shorts and a tan top, but I visualize myself with a robe for it. This so you can have a idea.