Something I learned many years ago from an old body and paint man : Fill a shot glass with lacquer thinner and set it on your bench . Check it every few minutes and as it absorbs moisture out of the air it will start to turn cloudy . The faster it gets cloudy the higher the humidity , but if after a half an hour or so it's still clear then it's save to paint . You learn with experience how much is okay for your particular paint .
It sounds kind of silly but it works great here since the humidity is rarely below 50 % .
And Bill is absolutely correct , if you are spraying lacquer and it blushes on you it will polish off .