Even though New England is known for its fall colors, the Pacific Northwest isn't a slouch. We can have displays of bright fall colors which we accent with the green of our firs and pines.
But we know that some years seem to have more color than others. Why?
It depends a lot on the weather.
The green of the summer leaves is caused by the presence of chlorophyll in the leaves. This is the miraculous chemical that combines sunlight with water with carbon dioxide to produce the sugars that feed plants.
As fall comes around cooler temperatures and most importantly the decreasing daylight trigger a change in the trees. These changes decrease the production of chlorophyll. As the green chlorophyll diminishes in the leaf other chemicals (that are there all summer) begin to show up. These chemicals are the same chemicals that give carrots and corn their color (yellows and oranges). When the chlorophyll decreases, they start to color the leaves.
At the same time, another type of chemical begins to be produced by the interaction of the sunlight and the sugars in the leaves. These chemicals are colored red and bright orange and tend to give leaves their most brilliant colors.
The ideal conditions to produce these colors are bright sunshine during the day, which will produce more sugars (with what is left of the chlorophyll) and convert the sugars to the red and bright orange chemicals. Then add cool, non-freezing nights that inhibit the flow of the sugars out of the leaves back into the tree.
This combination will give leaves their most dazzling colors And for best viewing of the colors you, of course, want a sunny day.
New England forests are dominated by trees that produce a lot of the bright oranges and reds (and sometimes purple) chemicals. And their colors are even more dramatic because most of the trees change color, where a large part of our forests stay green. But we still get some pretty good color, especially from the vine maple, slide alder, and sumac.