Was coming into LGA on DL 456 Sunday night (Jan. 13) in some of the thickest fog I've seen. We were delayed an hour in ATL because, according to the pilot, LGA was down to one runway and planes "were stacked up along the east coast waiting to land." We finally took off about an hour late.

Two questions:

1. Particularly once we got nearer to LGA, the number of planes visible in the sky out the window was stunning. I've seen three or four or five other planes many times, but this was something out of a gridlocked highway -- I literally counted 20 other planes visible just out my window at, I'd guess, 12,000 feet or so. I know there are rules and regulations about keeping planes clear of each other but how challenging is that in those situations? Any reason to be concerned?

2. Once we were cleared for landing, we began to descend pretty much into the fog - almost as if the whole plane was surrounded by white on all sides. After a few moments of descent, we suddenly began to ascend again and the pilot announced that he had not seen a "signal" from the ground - at least that's what it sounded like he said on the PA - and that we were going to circle around and try it again. We did, and landed fine (though it made me wonder what the minimum visibility a pilot must have to safely land? 1/2 a mile? Less?). Anyway, what signal was the pilot likely referring to?

Thanks, both for this post and all you do.