Tuesday, May 5, 2015

How the Louisiana Purchase Changed Weather History in the United States

Chris Dolce
Published: May 5,2015




 
A little more than 25 years after declaring independence from England, the weather history of the United States was changed forever after one of the most important land acquisitions of its early history was completed.
Thomas Jefferson made a deal with France in 1803 to gain the Louisiana Purchase, which was an expansive area of land that stretched from the Mississippi River westward to the Rocky Mountains. That deal essentially doubled the size of the country for a price tag of $15 million, or about 4 cents per acre, according to the Library of Congress.
A large chunk of the land the United States gained includes the Plains states, which gave the country a large area of prime farmland.
But for some meteorologists and weather enthusiasts, a map of the Louisiana Purchase may stand out for another reason: tornado alley.
When comparing the land area of the Louisiana Purchase to the National Severe Storms Labratory outline of the traditional Plains tornado alley, you can see a significant overlap in the geographical areas that they cover. This includes parts of Texas, Oklahoma, Kansas, Colorado, Wyoming, Nebraska, South Dakota, Iowa and Minnesota.
(MORE: What Tornado Season Looks Like in 5 Seconds)
We should note, however, that tornado alley has no firm boundaries, and the area it encompasses can vary some depending on the criteria used.
The Louisiana Purchase (yellow area) compared to the traditional Plains tornado alley from the National Severe Storms Laboratory (red area).




























That said, it's pretty safe to say that the annual average number of tornadoes in the United States skyrocketed with the land gained from the Louisiana Purchase.
Although the Louisiana Purchase makes up parts of 15 states, a total of six states are fully within its boundaries. According to the National Climatic Data Center branch of NOAA, the annual average tornado count from 1991-2010 was 350 for those six states alone, which includes Arkansas, Oklahoma, Kansas, Nebraska, Iowa and Missouri. That's about 28 percent of the annual average number of tornadoes for the entire United States over the same period (1253).
When including states that are not completely in the boundaries of the Louisiana Purchase such as New Mexico, Colorado, Wyoming, Montana, North Dakota, South Dakota, Minnesota, Texas and Louisiana, the annual average tornado count for the entire Louisiana Purchase is likely quite a bit higher. However, we don't have an exact figure since climatology statistics are not available for the partial portions of those states.
(MORE: Counties With No Tornadoes Since 1950)
Though it's tough to say what our country would look like geographically had the Louisiana Purchase never occurred, it's interesting to see how this huge historic event played a role in shaping our weather history.

MORE: How Many Tornadoes Has Your City Seen Since 1950?

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