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When Does Tornado Season Start?

Bennington, KS tornado. May 28, 2013.
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“When does tornado season start?”

Depending on who you ask, that question can bring back many different responses. For instance, if you ask someone from the southeast United States when tornado season starts in January — they may tell you its already begun. Ask the same person in North Dakota and they’ll tell you to wait until closer to June. 

The reason why these responses are different is because tornado season begins at different parts of the calendar year for different regions. This is due to the jet stream’s movement over the country. In the winter, the jet stream is further south typically. Because of that, colder air is locked into place across the northern parts of the country and the warm, humid airmass we need for tornadoes is locked away in the Southeastern US.

That is, if it is even there. Sometimes in winter, arctic air is so strong that it pushes the tropical air all the way through the Gulf of Mexico and into the Caribbean. That’s when we get our major winter weather events here on the Southern Plains.

As Spring arrives, that warm and humid airmass begins to build north and west. This is when the Plains get our tornado season.

So when does tornado season start?

January – February

This is when the Southeastern United States is most likely to see tornadoes. Of course, tornadoes can happen in many other places during these months. However for the sake of this article we are just counting most likely areas. There are typically big lulls in activity and even some years where there is very little activity in the southeast due to a colder winter in January and February. So when does tornado season start here could mean a lot of different things.

March

Tornadoes in March happen anywhere from the Plains to the Southeast to the Eastern US. There is a pronounced eastward bias at the beginning of the month on average. By the end of the month though, the Plains are coming into sharper focus for tornadic potential. The answer for when does tornado season start for us here in the Southern Plains is typically sometime in March.

April

By April, the Southeast to the Southern Plains are typically active with severe weather. For Texas, the mid-to-late April period is usually the prime time for storms and tornadoes everywhere but the Panhandle. In fact, in the Southern Plains, North Texas is the only area to see its typical tornadic activity peak before May.

May

May is the prime time for tornadoes and strong/violent tornadoes across the country. More tornadoes occur on average in the month of May than any other month on the calendar. May typically sees the highest tornado density on the Plains and High Plains. This is when we typically begin seeing our tornado season shift north out a bit. Oklahoma and Kansas both peak in tornadic activity here.

June-August

The summer months are when tornadic activity typically begins to slow down again. In June, the season is usually still rather active both on the High Plains and Northern Plains. The Texas Panhandle usually sees its peak of tornado season in June, which is the latest peak of activity in our region. This is because the jet stream has moved north and west and the Panhandles usually get the most energy at this point. Elsewhere, Colorado and Wyoming are active as are the Dakotas and into the rest of the Northern Plains and Midwest.

The Jet stream usually weakens during this period, so the occurrence of violent tornadoes is much rarer in the summer months.

September-October

The Autumn months bring a period of transition back to our weather. Whereas the typically stable but weaker northern Jet stream of the summer is replaced by a jet that is wanting to go back south for the Winter. This puts many areas from the Plains, to the Eastern US, to the Southeast back into play for tornadoes. This period can see big tornado events just about anywhere. But also this period can be exceptionally quiet if early cold fronts in this period or a weaker jet stream keep the ingredients for tornadoes from coming together.

November-December

By the beginning of the winter months, tornadic activity once again typically becomes confined to the Southern Parts of the US again. There are notable exceptions to this. A strong jet stream with warm and humid air can cause big outbreaks in places like the Midwest. November 17, 2013 in Illinois is one example historically. The Southern Plains have had a tendency to have a big tornado event in November every other year or so historically as well.

When Does Tornado Season Start Then?

If we are talking across the country, the answer is simple: it never stops.

When we are talking regions in a general sense, that answer does differ as our study of the calendar above shows.

The other big thing to keep in mind is just because tornadoes happen on average in a certain way does not mean they won’t deviate. Averages are there to indicate where events gather around. Big tornado events happen out of season often enough to say its not unexpected or irregular.

You should always be prepared for severe weather and have a plan!

Learn More About the Basics of Severe Weather Season Here

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