There are a few ingredients needed for thunderstorm development: moisture, instability and lift. For a storm to become severe, we also need wind shear, which is the change in wind direction with height.
All of these elements are never uniform in an atmosphere which means the life cycle and intensity of a thunderstorm will never stay the same. We hear it all the time, many folks say, “the thunderstorm just divided in two before it hit my town.”
There isn’t an invisible wall that keeps that storm out of your town, it’s just the luck of the draw. No matter how many times you see it. Sometimes it’s just the end of the life cycle in that particular storm… which in many cases can only be a 30 minutes to an hour. So if that storm forms far west of you, you shouldn’t be surprised if it dissipates before reaching your town.
Storms can also pulse. A strong storm can become weaker only to strengthen again based on the atmospheric conditions that are invisible to us.
Speaking of invisible atmospheric conditions… There are upper air winds that “steer” the storm. Storms can wobble and sometimes look as if they’re heading straight towards you when actually the upper atmospheric winds are pushing it around you.
There is no scientific evidence that suggests a town, river or lake can split or dissipate a storm. Splitting storms are so incredibly common. They’re caused by spinning in the upper atmosphere due to low pressure.
Something else to consider – what seems like a monstrous storm to us in person is actually a small phenomenon on the radar. There is always a small chance for a direct hit. But you should always take a severe storm seriously.