Why are thunderstorms associated with low pressure systems?

When air is falling down from high altitude into a region, that increases the pressure in that region and makes the wind blow outward. This is a high pressure region down at the surface. read more

When it's a particularly strong low, that means the air is rising very fast causing a very low pressure at the surface and bigger rain drops form (because the fast rising air suspends them longer so they can clump into even bigger rain drops and because more water is being carried upwards faster to make more rain). read more

Supercell thunderstorms are the strongest and the most associated with severe weather phenomena. Mesoscale convective systems formed by favorable vertical wind shear within the tropics and subtropics are responsible for the development of hurricanes. read more

When a low pressure system is just ahead of a cold front, the warmer, less stable air ahead of the front can become a thunderstorm inside the counter-clockwise rotating low pressure area. This is the situation that produces the most severe thunderstorms and shorter, heavier downpours seen commonly in the spring and summer in many areas. read more