I'm Dave Thurlow and this is The Weather Notebook. Rainforests of the world receive about ten times more rain per year than most parts of the United States and Canada, places where most of us live. If all the rain that falls in one year over the entire continent of North America was to be distributed evenly, each spot would get about 75 centimeters. Most rainforest locations however get well over fifteen times that amount, each year. Just for comparison sake here's a glance at the yearly rainfall in a few locations around the U.S.
The Southwest gets about 25 centimeters a year and folks in the southeast get over 125. The Northeast averages just under a hundred centimeters, with a quite a bit more up in the mountains; this is true in the northwest as well. North America only has one area of true rainforest and that's on the Pacific Coast in British Columbia. Rainfall there averages nearly 700 centimeters a year.
The difference between this extra-tropical rainforest and the tropical rainforests of the world is basically temperature. Tropical rainforests have an average annual temperature of over 30 degrees C, year 'round. Because the sunlight there is always so strong, the air heats up and rises, and mid afternoon thunderstorms pop up like clockwork. At any given instant, equatorial regions are getting hammered by tens of thousand of thunderstorms. Rainforests are actually so dense in places that the rain, and when it's not raining, the sunlight never make it to the ground. Therefore most of the nutrients and energy in the forest are contained in the tree leaves and branches, much like the temperate rainforests of the Pacific Northwest.
The Weather Notebook is made possible by a grant from The National Science Foundation. Additional support comes from Subaru, maker of the all weather Legacy. Subaru, the beauty of all wheel drive.