Tornadoes most frequently occur in the months of April and May, typically in the spring time, along the Gulf Coast. Although, that’s not to say one can’t spin up in the winter!
It’s an unusual time of year for tornados, but they can happen. Let’s look at how tornadoes happen, and how they happen in winter.
So how does a tornado form? The right ingredients have to be present.
In the month of January, we typically see cold fronts pass through, but the upper and lower level jet stream typically stays along the border of Canada and The northern United States. Sometimes the jet streams can dip far enough south and pick up speed along the low pressure trough and cause wind shear.
The jets dipping South causes a mixture of cold air in our upper levels clashing with warm air at our lower levels. This causes a significant pressure difference and provides energy for thunderstorms to form. That’s why when we see warm temperatures and sunshine before a thunderstorm — we know that will provide the fuel for a thunderstorm to thrive.
What really creates the threat of the tornadoes is if the low level jet happens to pick up speed around 750 mb. This creates strong winds in our mid-levels and wind shear in our environment. Wind shear is the change of wind direction and speed with height. That causes a mass of air to spin horizontally, like a slinky. If the low level jet is >75 kts, then we could have strong helicity levels. Helicity is a measure of spin in the environment.
Typically in the month of January there isn’t a vast difference of temperatures with heights, which is why we don’t see these stronger storms often. A way to see if we could see a thunderstorm form is the amount of CAPE, Convective Available Potential Energy, in the environment. Another way is to see how unstable our environment is.
The finally ingredient is the amount of lift, which is the updraft that then expands the column of spinning air. This causes the slinky to then turn vertical and causes a tornado to form.
What you want to do if you are ever in a tornado warning is head to an interior portion of your house and wait until you are given the all clear.
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