Air temperatures may vary greatly from day to day. Today's afternoon high temperature may be 5 degrees warmer than that experienced on yesterday afternoon, or tomorrow morning's low temperature is expected to be 15 degrees colder than what was recorded this morning. Some places in the country experienced similar changes yesterday as a major storm system affected the temperature patterns in the center of the country. How are these significant changes possible?
Many factors are at work in determining the near-surface air temperature at a given place and time. The daily variation in temperature is driven by the daylight and darkness cycle in solar radiation. Under clear skies, the day's maximum temperature typically occurs within an hour or two after local solar noon. Local noon is that time when the sun at most locations would be directly to the south of you and is at its highest point in the sky for that day. Clear skies will usually cause the daily minimum temperature to occur within an hour of local sunrise. If all other factors were equal, changes in the daily temperature pattern from one day to the next would be small because day to day changes in the incoming solar radiation typically are not large.
Cloud cover could complicate the situation - lowering the afternoon temperatures because of the blocking of at least some of the incoming solar radiation, and reducing the drop in overnight temperatures because the clouds absorb the outgoing thermal radiation from the earth and radiate much of it back to the surface.
A third factor affecting the day to day temperature variations is the role that the general wind flow has upon local temperatures. Many times the observed large swings in temperature from day to day result when warm air from some distant locale replaces the cooler air that has resided in the area. This replacement causes a warming. Conversely, if colder air invades, a noticeable temperature drop results. These examples are termed "warm air advection" and "cold air advection", respectively, and could be more significant than the other two factors identified above. Warm air advection can occur with the passage of a warm front and a warm air mass is ushered into the region. A less dramatic change would occur when the winds turn to blow from a warmer region as a high pressure system pulls away from the region. Conversely, cold air advection would take place after a cold front passed and a cold air mass makes its influence felt. For more details describing how you can use a surface weather map to determine regions of warm or cold air advection, consult DataStreme Activity 4A and Tuesday's optional electronic Supplemental Summary Information .
To be submitted on the lines for Tuesday on the Study Guide, Part B, Applications, Week 4 Chapter Progress Response Form, under section B. Daily Summary.