I was trying to come up with some playable weather gen rules with my son last night and made some simple rules, but still more complicated than need be. I then simplified them even more. I don't know how realistic this may be, but I think it can help generate some interesting variations in weather on the fly.
1 or 2 = worse weather
3 or 4 = average weather
5 or 6 = better weather
If worse weather, roll 1d6
It is bare bones. Please let me know what you would change.