Max Temp

A common misconception, is that it must be coldest in the middle of the night, and warmest around midday. On some occasions, mainly due to air mass changes, this may be correct, but not usually. The lowest (minimum) temperature usually occurs a little while after sunrise, and the highest (maximum) temperature usually occurs after midday --- sometimes as late as 3 or 4 hours after midday.

To understand why, it is necessary to consider that thermal energy during the 24 hours is radiating continually from the surface of the earth (at long wavelengths), and incoming solar (relatively short wave) radiation obviously only when the sun is above the horizon. With the sun below the horizon (night), outgoing radiation allows the surface to cool, and the temperature drops. After sunrise, incoming solar radiation counteracts this loss of heat, but only after a lag - which can be up to an hour or so in winter with a low solar elevation.

The minimum temperature occurs when there is a balance between outgoing and incoming radiation. As the sun rides higher in the sky, increasing amounts of short-wave radiation are available to heat the ground, and therefore available to heat the overlying air. Although outgoing land-based radiation is also increasing, solar heating is dominant. The temperature rises, until, past noon, incoming solar radiation starts to decline again.

The highest(maximum) temperature occurs when heat gain due to incoming solar radiation, and heat loss due to outgoing terrestrial radiation balance: this occurs some time after midday.