An area of low atmospheric pressure produced from continued surface heating as in the Desert Southwest. As the air is heated, it expands, becomes less dense and thus the pressure becomes lower.
(Or heat low.) An area of low atmospheric pressure near the surface resulting from heating of the lower troposphere and the subsequent lifting of isobaric surfaces and divergence of air aloft. Thermal lows are common to the continental subtropics in summer; they remain stationary over the warm surface areas that produce them; their cyclonic circulation is generally weak and diffuse; they are nonfrontal. Compare monsoon low.
An area of low pressure due to high temperatures caused by intensive heating at the earthâ€™s surface. Thermal lows are common to the continental subtropics in summer. They are non-frontal, weak and diffuse remaining fairly stationary over the area that produced them.