, Bill. However, "ambient temperature" simply refers to the temperature of whatever surroundings you are talking about (whether it be outside, in your den, or in your fermentation fridge).
I gradually raise the temperature as fermentation slows, until I get to my "final" temperature. To illustrate, I may start my fermentation in a roughly average temperature range of 65F. Over the couple days or so that the fermentation is very active, I won't touch it. Then, as the fermentation slows, I will bump the ambient temperature up to 68 or so over a couple days, to help ensure that the yeast remains active. Often, at the tail end, when fermentation has slowed to a crawl (say, one bubble every ten seconds, but I am not that exact about it), I'll raise the temperature up to the high end of the yeast's range (say, 72F) to help ensure full attenuation and post-fermentation cleanup.