An outflow boundary almost always extends down to the surface (aka gust front). When the boundary interacts with land (even land that is not elevated to any significant degree) the air is forced aloft and convection occurs. Florida is well known for its summer thunderstorms activity - initially caused by landmass heating, but when two outflow boundaries from separate storms collide, the air is again forced upward, sometimes violently, and new thunderstorms develop. During summer when steering currents are often very light, the seabreeze from the Atlantic east coast moves inland to the west during the late afternoon while the seabreeze from the Gulf west coast moves inland to the east. They collide in central Florida and thunderstorms pop up along the spine of the peninsula.
Cheers,
ED