the Americas varies significantly from region to region. Tropical rainforest climate occurs in the latitudes of the Amazon, American cloud forests, southeastern Florida and Darién Gap. In the Rocky Mountains and Andes, dry and continental climates are observed. Often the higher altitudes of these mountains are snow-capped. Southeastern North America is well known for its occurrence of tornadoes and hurricanes, of which the vast majority of tornadoes occur in the United States' Tornado Alley, as well as in the southerly Dixie Alley in the North American late-winter and early spring seasons. Often parts of the Caribbean are exposed to the violent effects of hurricanes. These weather systems are formed by the collision of dry, cool air from Canada and wet, warm air from the Atlantic. Hydrology With coastal mountains and interior plains, the Americas have several large river basins that drain the continents. The largest river basin in North America is that of the Mississippi, covering the second largest watershed on the planet. The Mississippi-Missouri river system drains most of 31 states of the U.S., most of the Great Plains, and large areas between the Rocky and Appalachian mountains. This river is the fourth longest in the world and tenth most powerful in the world. In North America, to the east of the Appalachian Mountains, there are no major rivers but rather a series of rivers and streams that flow east with their terminus in the Atlantic Ocean, such as the Hudson River, Saint John River, and Savannah River. A similar instance arises with central Canadian rivers that drain into Hudson Bay; the largest being the Churchill River. On the west coast of North America, the main rivers are the Colorado River, Columbia River, Yukon River, Fraser River, and Sacramento River. The Colorado River drains much of the Southern Rockies and parts of the Basin and Range Province. The river flows approximately into the Gulf of California, during which over time it has carved out natural phenomena such as the Grand Canyon and created phenomena such as the Salton Sea. The Columbia is a large river, long, in central western North America and is the most powerful river on the West Coast of the Americas. In the far northwest of North America, the Yukon drains much of the Alaskan peninsula and flows from parts of Yukon and the Northwest Territory to the Pacific. Draining to the Arctic Ocean of Canada,