thermal low

A low-pressure area that forms near the ground due to intense heating of it. Thermal lows are typical of summer, when insolation is at its greatest. As the ground heats up strongly, the air in contact with it also warms and, as its density decreases, it begins to rise. The gap left by that air as it escapes upward is immediately filled by air from the surrounding area, resulting in the formation of the thermal low.