Learning to Fly - Fog and Mist

Friday we had a very early lesson, because the instructor wanted to spend the day with his family. I decide that since I can see fog, I had better call and check in with him, to see if flying is even possible today. No answer comes back to us and so we head out. On the way, we hit pockets of fog around my valley, but things get a bit better when we hit the Newhall Pass. You could not see the mountains in the valley, but you could see. So we get there and the instructor has the doors open and immediately after seeing us, he pulls the plane out of the hanger. He has the flight weather up on his board and as soon as my son sits down, he points to it and asks my son if they will be flying today. Visibility is right on the edge of good, 3 miles and yes, they are OK. So then the instructor says, what happens if visibility gets worse, like down to 2 1/2 miles, while we are in the air? My son says something about asking the tower for an exception, since he isn't IFR (instrument flight rules) rated and the teacher then shows him how to request such a thing. Then he mentions the dew point is at 8 degrees Celsius, when might the plane end up with icing on the wings? My son immediately answers "At 4 thousand feet". (Please note that I did not understand this at the time, but my son explained to my husband and I at dinner last night, that the temperature drops 2 degrees for each thousand feet of elevation, thus the air is 8 degrees colder at 4 thousand feet and so it is at 0 degrees Celsius, at that point. Which is freezing and thus, you would have ice forming on your wings at that altitude.) Since they were just going to do pattern work today, they did not have any problem with that low ceiling. If they had been flying over the mountains around the valley, they would have. So up they go and leave me to my work. It is very quiet here at Van Nuys. Only 2 planes take off and just a few land, my son's being the one doing most of the business. They do what they have to do and they are back in about 45 minutes. I was surprised they were so early and the teacher says, very good work today to my son. The preemption's the past 2 weeks did not adversely effect him and he actually was building on his skills today, not just trying to recover them. They were both very happy at the end of the lesson.
As promised, the Santa Ana's are blowing a bit today, but are scheduled to die down around noon. Hopefully he will get in his 3PM lesson today. I already warned him that the airport will be incredibly busy and so will the skies today, on this final day of the Thanksgiving holiday. He is mentally prepared for that. Hopefully he will have a good flight today.