Diurnal heating is the daily warming of the ground, and the air just above it, by sunlight. It drives the day-to-night cycle in temperature, low-level mixing and instability that shapes when thunderstorms are most likely to form.
How the sun warms the lower atmosphere
Sunlight heats the ground, and the ground warms the air above it. Over land in fair weather, this gives the atmospheric boundary layer a marked daily cycle.
During the day, a well-mixed layer of vigorous turbulence grows deeper, capped by a stable zone at its top. In strongly convective conditions, such as over deserts, the boundary layer can reach several kilometers deep, and the daily temperature peak usually comes after local noon.
Why storms favor afternoon and evening
As the lowest layer warms and mixes, surface air becomes more buoyant, and storms that need surface-based instability get their best chance. NSSL (the National Severe Storms Laboratory) notes that thunderstorms are most likely during the afternoon and evening hours.
The American Meteorological Society (AMS) Glossary describes the same pattern in clouds and precipitation, which increase by day and decrease at night over land. Over water the cycle reverses, though to a lesser extent.
Heating adds instability, but storms still need moisture and a source of lift such as a front, a dryline or terrain. Morning clouds, lingering rain-cooled air or early storms can cut heating short and change the afternoon outcome.
What happens after sunset
Under clear skies at night, the ground loses heat to space and cools the air touching it. A stable nocturnal boundary layer forms, typically a few hundred meters deep, with a temperature inversion near the surface.
That stable layer cuts surface air off from the warmth and mixing of the afternoon. It is one reason storm coverage over many land areas drops after dark.
Why some storms keep going at night
Storms can still form or persist at night when they draw on air above the cool surface layer, a setup called elevated convection. A common partner is the nocturnal low-level jet, a wind maximum just above the nocturnal inversion that is typical of the south-central United States in late spring and summer.
The National Weather Service (NWS) glossary notes that nocturnal thunderstorms are often tied to a strengthening low-level jet and are most common over the Plains. A NASA scientist, quoted in a 2020 NASA article, said the Great Plains receives about half of its summer rainfall at night.