The Great Plains and Prairies region has a continental climate which means it has very diverse weather during the changing of the seasons. The summer are very warm, and the winters are very cold. There is little precipitations and humidity. The plains have an average rainfall of 15 to 25 in annually; northern receiving approximately 12 - 15 in, the eastern section about 25 in, and the western section receiving less than 15 in. The region receives more rain in the summer than in the winter, except for the northwestern section. It also has a lot of wind with sudden temperature changes. The Gulf of Mexico is the main source of moisture, and it falls off to the north and west. The southern section, in Texas, has an average growing season of 240 days.
Since the Great Plains and Prairies region also stretches so far north and south, the latitude also plays a role in the temperature. The temperatures more southern are going to be much hotter, while the northern temperatures are going to be much colder.
In this map of the US part of the Great Plains and Prairies region, you see how the it lies just east of the Rocky Mountains. At least half of the region falls under the rain shadow of the Rocky Mountains. This means that the moisture and rain from the Pacific Ocean that flows up the Rocky Mountains from the windward side dries up using the adiabatic cooling process as it flows up to the top of the mountain and then back down the other side. By the time it reaches the leeward side all the moisture is gone and all that flows down is dry, warm air.
In Canada, the prairie region alternates between sunny, warm and dry days with cold nights. The temperatures get much colder in Canada because it is more northern, and the top north of the region runs into the Arctic Ocean. The warm winds, called Chinook winds, and thunderstorms. The Chinook winds happens only in winter. They are a warm, dry wind blowing down the eastern slope of the Rocky Mountains and are able to raise temperatures up to 30 to 40 degrees F in just a short period of time.
The southern section of the Canadian Prairie receives 10 - 20 in of rain annually, and has a growing season of 70 - 110 days. It has an average growing season of 120 days at the U.S. Canadian border.
The regions is also known for it's extreme weather. Tornadoes occur in the Great Plains more often than any other place on Earth. The mountain ranges running north to south create the perfect conditions for cold try air to travel from the north and collide with the warm moist tropical air coming from the south. The jet stream flows south across the great plains seasonally, and this is another key player in creating tornadoes. Combined, most occur in the area of Kansas towards eastern Nebraska and Iowa; aka Tornado Alley. Most occur inside the state of Texas. Tornado season peaks in May in Tornado Alley, April in Texas and Oklahoma, June in Nebraska, and late July into early August in the Southern Prairie Provinces. About an annual average of 524 tornadoes take place within the Great Plains region.
A very interesting fact about the location of the Great Plains is that 100th meridian line of longitude runs almost directly straight through the middle. This meridian is viewed as the line that separates the arid western part of the United States from the humid eastern side. Whats both interesting, and scary, is that since the 1980's the climate barrier that used to rest right on top of the line has been slowly drifting eastward, creating more arid conditions through the United States. The climate barrier has moved about 140 miles east. No harm to farming has been caused as of yet, but if it continues the Graet Plains will see a rise in temperatures and altered precipitation.
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