Hot Air Balloon pilot reports encountering fog approaching from the east and quickly descends to minimum altitude and lands in the first available landing space. Visibility had dropped to about a mile at the time of landing.

Narrative

While at a balloon event we were to do a fly-in task towards the balloon field. The event went on a weather hold for a while and it was later decided that the weather had cleared enough for us to go out and find a site to fly from that would put us over the target on the launch field. I went south of the field a few miles and found a home where I could fly out of their front yard. The weather was quite clear with at least 3 miles visibility on my take-off and no clouds overhead. I headed west for the first 500 FT of altitude and then turned towards the north above that height. As I was heading to the north; I noticed some low level fog moving in from the east/northeast and I immediately went down to a lower altitude to hug the treetops until I found a clear field to land in. My visibility had dropped to about a mile or a little better upon my landing. After I landed; I received a call from a fellow pilot on the launch field asking me if I had flown; and if so; was I on the ground. I informed him that I was flying until I saw the fog moving in. I landed at the first opportunity I had. I was just south of the heavier fog and never felt I was in any personal danger. I had no intention of flying in or near fog that morning; it just moved in unexpectedly from a distant storm area.