How does one create the danger zone known by meteorologists as "Tornado Alley"?

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The "Alley" is the mixing of three different airs--cold, dry air, probably from the poles; warm, dry air from the Southwest and warm, moist air from the Gulf of Mexico.

In this alternate Earth, North America is arranged quite differently.

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First off, the Appalachian Mountains don't exist, and there is no evidence that they ever did. The Rockies have gotten taller--the tallest peak being 20,310 feet above sea level. The big splotch of red stretching from Canada to Mexico is the resulting plateau, varying in elevation above sea level between 3300 and 16,000 feet.

In this diagram, we find the Midwest subject to the collision of two different airs--warm, moist air from the Gulf of Mexico and cold, moist air from Hudson Bay. When these two airs collide, will we see any difference in Midwestern weather? If yes, then to what extent?