Yesterday 9/24/00, I viewed some aircraft approaching EWR over my home. This was the first time I notices that there was a short stream of something trailing from the middle or so of the wings. I know it was not from the engines because, it was on an MD-80 as well as 737's and such. This occured to all aircraft that passed over yesterday. They have passed over before and it has never happened, or at least I have not seen it. Yesterday was a partly cloudy day at EWR and I don't know if that would have something to do with it. My friend seem to have his own thoughts for the trailings. One is that it is water vapor from the clouds. He claims: "When the planes fly through clouds, they get wet. Then when it's landing, air makes it evaporate (makes steam)". Keep in mind my friends are not that knowledgeable in aviation. I know that many people probably know the answer to this question but I do not. Does anyone have any info for me?