This interests me on two levels.
Firstness, during the course of losing most of my weight (the first 170 lbs or so) I would definitely lose it in "fits" (what you guys call a "woosh"). It became quite predictable: I would basically hover around a certain weight +/- 0.2-0.6 lbs for a few days or more then BAM, 2-4 lbs gone overnight.
Now I'm at 210-ish and the change in fat is much more visible. I have an extremely strange fat distribution (best described as "leftovers"
) and I can usually see one lb gained or lost before I weigh myself, especially when observing a couple key places.
That being said, I've also noticed this change in "composition" of the weight. The "fat" seems to get softer and and the sensation felt in the part being touched is also different. More sensitive, I think.
The water "exchange" thing makes a lot of sense (or at least provides a good visual for the internal workings of these changes). I'll try and mess with my sodium and water intakes (and ratios?) to see if I can give you anything useful. I wish I had read this earlier, since I would have been able to provide a better anecdote had I changed these variables when I was losing most of the weight.