The coldest time of day is usually just after sunrise due to the Earth’s heat loss and gain patterns. However, weather patterns can cause the coldest temperature to occur at any time during the day.
While some may believe that the coldest time of day is at midnight, or a little before sunrise, this is generally not true. The coldest part of the day is usually just after sunrise. However, there are some times, especially in the winter, when the coldest temperature may not be during this morning period. Weather patterns can play a role in determining when low temperatures hit during the day.
To fully understand why the coldest time of day is just after sunrise, it’s important to understand how the Earth receives and loses heat. The planet is constantly receiving radiant heat from space and returning it to space. The vast majority of the heat the Earth receives comes from the sun. Heat is gained during the day and lost during the night. However, just because it’s night in your location doesn’t mean the whole Earth is losing heat. One side is losing heat, but the side facing the sun is gaining heat.
When the sun rises, the part of the Earth that is just starting to receive the sun’s rays is still losing heat. As with any property governed by inertia, it takes some time to reverse this trend. Meteorologist David Cook of Argonne National Laboratory explains that “Because the sun is so low on the horizon at dawn, most of the energy is absorbed by the distant atmosphere.”
However, the weather changes from day to day and the coldest temperatures may not always be during the period just after sunrise. In some cases, a cold front may pass through a location, leading to cold temperatures at any time during the day if the front is powerful enough. If this happens, the coldest period will probably be in the hours following the passage of the front.
In general, this cold front scenario is very rare. It can only happen a few times a year in many locations. At lower latitudes, that may never happen. It’s safe to say that, in most cases, the coldest time of day is usually just after sunrise.
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