When thunderstorms split or end right before hitting a town or county it has less to do with the location and more to do with the fluid evolving nature of a thunderstorm. A basic thunderstorm typically lasts for around thirty minutes to an hour. A supercell or much larger storms can last much longer and can move fast across several counties or even state lines in several hours however, they all come to an end at some point. The thunderstorm is powered by the updraft which takes in warm and moist air which is the fuel for a storm. When the storm encounters a body of water like an ocean or lake they often take in cooler air which can weaken the updraft and dissipate the storm. If they run into drier air, that can help shut off the updraft as well. Sometimes when the updraft is weak, the downdraft will take over and slowly dissipate the storm. So there are several ways a storm will dissipate.
There are instances of splitting storms. The science behind this is pretty fascinating. It happens in environments with strong wind shear. That’s the change in direction of the wind with height. A storm can split when the top moves in the direction of the upper atmospheric winds and the base of the storm moves in the direction of the lower or surface winds. This will eventually cause one area of low pressure to split in two causing two updrafts and two storms. In the Spring and Summer there is more water vapor in the atmosphere and humidity than in the winter so that is why there are often a lot more thunderstorms. As you can tell weather is often very fascinating and complex which is why I love it so much!
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