A usage poll for the word "dissipate"

If I were to say "the fog dissipated around 11 a.m." would you think I meant:

a. Around 11 a.m. the fog almost completely or completely disappeared; or
b. Around 11 a.m. the fog grew lessened by some amount, even if it was minimal.

Just curious since I got myself momentarily involved in a Pit thread and in reading over it again I think much of the disagreement rests on different people viewing the word as meaning only A and others as only B.

I know that in common usage (and ever per dictionaries) both are valid (why shouldn't we use the same word to mean wildly different things? it is what makes the world love us) but I think it is clear that the original use meant A and I'd say that 90% of the time I use the word that is what I mean (unless it is in the phrase "is dissipating" in which case I mean it is on its way to completely disappearing but may not have gone far down that road yet.