what could it mean for the weather to be good for fishing

The phrase “is the weather good for fishing?” is found in the sixth chapter of the book “Number the Stars”. After the Nazi officers visit the Johansen house at about four in the morning in search of the missing Rosens, the Johansens decide to take the children away to live with Uncle Henrik for some time. They fear that the German soldiers would come back in search of the Rosens. Mr. Johansen then makes a phone call to Uncle Henrik, and says the following things to him:
“So, Henrik, is the weather good for fishing?”
"I'm sending Inge to you today with the children, and she will be bringing you a carton of cigarettes.”
Annemarie who is listening to her father's conversation with Uncle Henrik knows that what her father is saying is not true, as cigarettes were hard to come by in Copenhagen. In fact, her father, together with his male friends, often complained of the lack of cigarettes in stores. She figures that her father is talking in coded language to Uncle Henrik. The phrase “is the weather good for fishing?” questions Henrik whether it is safe for the Johansens to take Ellen over to his place. Ellen would probably be safer there than in Copenhagen. The “cartons of cigarettes” refers to Jews. Mr. Johansen explains to Henrik that they were sending “only one carton of cigarettes”. This means that Ellen would be the single Jew visiting Uncle Henrik.