I literally just signed on to make a post that my car is having this problem. I live in the Pittsburgh, PA area (please no Steelers comments) and I just noticed this problem on my Jeep the past two days. I have a WJ / 2003 Grand Cherokee v6. Yesterday in Pittsburgh the temperature was about 35 degrees and very humid, light rain / misty, and then started to snow later. There wasn't a lot of water on the road, but enough that I had to mildly use my wipers.
When I stopped the Jeep at a parking spot, I saw a white steam coming from the hood. It was not a black smoke but definitely more of this white steam / smoke that everyone else has mentioned. The hood of the Jeep was not overheated or hot, the inside area around the radiator didn't seem overheated, and the temp gauge appeared in the normal heat range. The white steam was coming from the driver side of the hood (if you're facing the hood, the middle-right side), which is right where the Radiator cap is located.
I guess this is a benign problem? The consensus appears to be this is just an evaporation of moisture on top of the Radiator. It seems very strange that this is just something to "let go" and not to correct. However, I have read here that others have looked for pin-hole leaks in the radiator cap or leaks in the tubes but didn't find anything.
I'm trying to be cautious here because the cooling fan relay has gone twice in my WJ, the first time I didn't realize the issue and I had serious overheat issues before I was able to power down the vehicle. So I'm fearful the cooling system in these WJs isn't the best...