METEOROLOGIST JEFF HABY
The difference between the high and low temperature is often between 15 and 30 units of F. Much of this difference can be attributed
to the daily cycle of sunlight and darkness. Other example factors include cloud cover, fronts, wind direction influences, humidity
and weather events. Sunlight though typically accounts for much of the difference when averaged over a year.
The high and low temperature is one of the important pieces of weather data that is included with a weather summary. Sunlight helps
warm the temperature thus the high temperature typically occurs when the sun is out and cumulative warming from the sun has taken
place. The low temperature typically occurs at night when radiation cooling lowers the temperature gradually at night. The lowest
temperature typically occurs around sunrise.
The significant difference in temperature between the high and low temperature due to sunlight makes this factor a weather changer. It
is the most common weather changer since it happens each day. Some days are more influenced by the sun than others. On days with thick
clouds and the same air mass, the difference between the high and low temperature may only be a few degrees. On clear dry days, the
difference between the high and low temperature may be 10s of degrees F, such as a morning low of 65 F and a high of 95 F. Clear
skies, long hours of daylight and dry air (and dry soil) allow for the maximum of warming by the sun. Thus, desert and semi-arid
regions tend to have the biggest difference between the high and low temperature. For example, the low temperature could be 50 F
with a high of 90 F in a arid location which results in 40 units F of warming due to sunlight. A humid location with significant
cloud cover and wet soils will reduce the amount of warming, though it can still be 20 units of F or more of warming
that can be attributed to sunlight.