|WX AND TIME OF DAY: AFTERNOON
METEOROLOGIST JEFF HABY
Afternoon extends from noon to sunset. Since sunset time varies significantly depending on season and latitude, the sunset time for most locations
will be in the range from about 5 pm to 9 pm. Thus, afternoon will typically be short in the winter but can be very long in the summer. This
writing will focus on weather generalities that occur in the afternoon hours.
This time of day typically has the warmest temperatures. Heating is cumulative throughout the day thus the maximum temperature for the day
usually occurs around mid-afternoon. At this point in the day the sun is still high enough in the sky to continue to warm the surface and
with the addition of the solar energy that has accumulated up to that point. If the atmosphere becomes unstable, it is the afternoon that
the atmosphere is most likely to become unstable and be the most unstable. Thus, thunderstorms and severe thunderstorms are often most
frequent this time of day.
The atmosphere near ground level tends to be well mixed in the afternoon due to rising thermals from solar heating. There tends to be at least
some wind this time of day due to the mixing of the air. Rising thermals will also promote cloud growth this time of day. Many days will
start off sunny but be at least partly cloudy by afternoon due to the rising thermals. This is especially true if plenty of moisture is
in place. If it is stable with moisture in place, the opposite may occur where the morning starts off cloudy and then it is sunny by
afternoon due to solar energy mixing out the saturated air.
Since temperatures are typically warmest this time of day, the relative humidity tends to be lowest. The drying power of the air will
tend to be highest in the afternoon. Items that need to air dry will tend to dry fastest in the afternoon, especially if exposed
to solar energy. Once the sun rises and mixes out the cool and stable air right at the surface, wind speeds can pick up significantly.