Let’s just begin this lesson with a simple tip: mother nature knows no calendar.
As we observe the changing affects of how severe climatology continues to shift on our warming planet, that fact will still be true even in a warmer planet. Big time severe weather does not care when ‘storm season’ is.
There have been deadly severe weather events in every calendar month — but storms are more frequent in the warm season months of April – September.
What are the peak months of severe weather?
Generally speaking, the majority of severe weather reports typically occur throughout the warmer season months from April to September. However, big severe weather events happen outside of that window relatively frequently.
This is especially true in the southeast US, where tornadoes tend to rise in frequency as the summer wanes and the jet stream dips back south during the winter months.
This is an important point to note, as severe weather typically ‘peaks’ at different times in different places.
In the Southeast, the peak tends to be February through April. On the Southern Plains, April and May are the peak months. On the Northern High Plains, the season will tend to peak in the summer months of June through August.
Storm season is a year-round affair.
The most favorable areas for severe storms are east of the Rocky Mountains in the US. The vast majority of big severe weather days will occur in between the Appalachian and Rocky Mountains — with the most frequent area for tornadoes running from Alabama back towards Kansas.
So where is tornado alley?
Depending on who is asking, the answer to where is tornado alley varies greatly.
Who is asking? Why are they asking? Where are they asking from?
Much of the United States lives under a near constant yearly threat from tornadoes spawned from supercells.
The answer to where is tornado alley is actually quite complex.
Air Masses Collide
Traditionally, tornado alley is located across the middle of the country in the region known as the Great Plains.
The Great Plains are where most people think when they think of tornado alley, and for good reason.
Each Spring, air masses collide to form towering thunderstorms on the Great Plains. These thunderstorms produce hail, damaging winds, and tornadoes.
Tornadoes form when these varying air masses combine over the Great Plains. Hot and dry air moves over the Great Plains from the southwest. That air meets warm and moist air, carried northwards from the Gulf of Mexico. Overhead, cold air carried by the jet stream creates an atmosphere that is highly unstable. Where these masses of air meet is what is known as the dryline. Because of this, the dryline is located most predominantly each Spring on the Great Plains.
The dryline is responsible for the most violent and photogenic storms and tornadoes on Earth. Drylines are a favorite of storm chasers.
Traditional Tornado Alley
In reality, there is some truth to the old definition. The traditional alley lays across the middle of the country, from Canada to Mexico.
Tornadoes form most frequently in the spring months, from April to June. Typically, tornado season’s climax occurs in mid to late May each year.
However, tornado season’s do not always follow the same path. Some seasons explode violently with over 1000 tornadoes. Other seasons quietly sputter, with only a few hundred tornadoes over open lands.
Consequently, tornado alley’s location changes from year to year.
More importantly, tornado alley is not just the region known as the Great Plains.
Coining the Phrase
The term tornado alley was used first in 1952 by US Air Force meteorologists Major Ernest J. Fawbush and Captain Robert C. Miller. They used the term as part of a study of extreme weather events from Texas to Nebraska.
From there, tornado alley was also used in a headline in a New York Times article published May 26, 1957. The region known as tornado alley was defined as Texas, Oklahoma, Arkansas, Missouri, and Iowa in that article.
Expanding the Definition
Given the realities of a warming planet and the likelihood that tornado activity will continue to shift and expand in areal coverage, we should expand the definition of tornado alley.
Tornado Alley is not located just on the Great Plains. Tornadoes frequently form across a larger portion of the country. This land area covers much of the United States.
Tornado Alley actually lays across a broad portion of the middle and eastern part of the country. In fact, tornado alley is located between the Rocky Mountains to the west, and the Appalachian mountains to the east.
In this region, tornadoes form at a pace unlike just about anywhere else on earth.
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