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Here is how the meteorological danger zone called "Tornado Alley" is made:

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Warm, moist air from the Gulf of Mexico mixes with cold, dry air from the mountains and warm, dry air from the southwest. And that is why the United States has such a high concentration of the Reaper's Scythe (or, at least, the perfect excuse for PTSD.)

But suppose, in an alternate Earth, that the West has more water. It doesn't matter where they come from, for that's not really relevant to the question. The Great Basin and the Columbia River Basin have become nothing but seawater. Back home, the Atlantic Seaboard, a watershed stretching from Nova Scotia to Florida, covers an area of 277,000 square miles. The Florida Peninsula, which is two-thirds of the state, is 65,755 square miles in area. The Gulf of Mexico is 600,000 square miles of seawater. But on this alternate Earth, the Atlantic Seaboard is 720,000 square miles of land, the Florida Peninsula 170,304 square miles (so would it still be a peninsula?) and seawater still makes up 231,661 square miles of the Gulf of Mexico.

I made this scenario with two goals in mind:

  1. Reduce or, more preferably, eliminate the threat of Tornado Alley
  2. Retain the Midwest's prairie fertility

Would these described changes check both goals out?

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  • $\begingroup$ There has been some recent indications that tornado ally has been moving east the past 30 years, partly because of drought in the SW becoming more severe. accuweather.com/en/severe-weather/… $\endgroup$
    – UVphoton
    Jun 5 at 17:29

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The way to accomplish these changes would be to not have either of the two Rocky Mountain building events. When the Atlantic Ocean first started opening up, the western part of the US was under water and rivers ran from the Appalachians to the sea - in the west.

The Sevier Orogeny formed the first set of mountains but most of them were eroded away. https://en.wikipedia.org/wiki/Sevier_orogeny The current Rocky Mountains were made in the Laramide Orogeny. https://en.wikipedia.org/wiki/Laramide_orogeny You might also want to get rid of any coastal ranges that might try to form.

Without the Rocky Mountains, the weather pattern is radically different. You would have the possibility of rain moving from the west till the clouds hit the Appalachian Mountains and dumping a lot of water there. Unfortunately, you are just as likely to have a desert in the same areas as desert today - 30th parallel. In the geological record, there is a lot of sandstone which is formed after sand dunes were marching over the land.

Unfortunately, these changes would affect the Midwest's prairie fertility. It may be less of a prairie and more of woodland - because of the extra rainfall. It might compare to the Amazon jungle but in a more temperate zone. Also, if the mountain building didn't happen with any attendant volcanism, you might have poorer soil.

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