From Glossary of Meteorology
(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 have generally weak and diffuse cyclonic circulations and often have thermal surface troughs of low pressure extending from them but are nonfrontal. Recurring thermal lows and thermal troughs are common to the continental subtropics in the warm season and remain stationary over the warm surface areas that produce them. One example of an area that frequently experiences thermal lows/troughs is the southern Oregon–Northern California coast, with pressure often increasing poleward. There, the feature has major implications on temperature, wind, and humidity across the Coast, Cascade, and Siskiyou–Klamath mountain ranges, which can create dangerous fire weather conditions and hazardous conditions in coastal waters.
Term edited 2 November 2020.