1) When the temps drop below zero at night trout know winter is around the corner and they usually feed accordingly. Trout remember how long and cold winters are around here and they've learned that the more insulation you go into winter with the better. When these trout strap on the feed bag you don't want to miss it.
2) As the water temps drop so too does a fish's metabolism. Now even though they're feeding aggressively, trying to put on weight for winter, they aren't at their fastest or strongest. This isn't something that you should be disappointed about though. Those giant rainbows that snapped you off on that first blistering run are apt to still take you into your backing multiple times, but now at least we stand a far better chance of landing them and not just that smash and grab that leaves you wondering what on earth just snapped you of....
3) Lets be honest when the mercury drops so too does the number of anglers on the river. Nothing like having a little more water to yourself, and less pressure on the fish ;-)
4) Backswimmer falls. Many people have heard the term but have never seen or experienced the spectacle that a backswimmer fall is. Backswimmers are air breathing insects capable of flying. They reside in every pond, puddle and ditch around, but when we start getting hard frosts at night these insects know they won't be able to survive the winter in the smaller bodies of water so they migrate to larger lakes and rivers, such as the Bow. Cloud like swarms of backswimmers migrate to the river and drop to the surface dimpling the water like falling rain. When backswimmers fall to the surface they'll often get trapped in the surface film and its one of the few times you'll see rainbows feed so voraciously. I've watched rainbows tearing back and forth, with dorsals protruding from the water like sharks on the feed. They slash and feed ultra aggressively trying to capture as many backswimmers as possible before they dive below seeking the cover of vegetation and rocks on the bottom. The shear biomass makes backswimmers a large and easy part of their fall diet. Anytime they can capture them on the surface, where they're sky lined and vulnerable, instead of having to hunt down a fast and erratic swimmer that can utilize all the vegetation as cover, so they take full advantage of that situation.
5) Fall is all about biomass. Although BWO's may be tiny in the fall, they are available in prolific numbers. The water can literally look furry in fall, blanketed with tiny BWO's. No matter their size the shear number and how readily available they are make them a prime reason for over eating. Hey if you eat nothing but handful after handful of smarties all day long for weeks on end theres a good chance you'd hear people calling you a fatty too ;-)