If your plotter is well trained, experienced, and conscientious, many errors will be spotted and corrected before your analysis begins. The plotter must always check with you before making any changes to reports. Our weather is constantly changing, and even when it appears to repeat itself day in and day out, changes are occurring. The changes that occur in the daily 24-hour cycle are known as diurnal variations. These variations must be known to more effec-tively evaluate the weather data on the surface chart . .
Temperatures reach their maximum in midafternoon and their minimum near sunrise.
The swing in temperatures is much greater over land than at sea, and in general, as the distance from water increases, the average diurnal temperature range also increases. . They are greatest and more uniform near the equator. Wind velocities reach their maximum and minimum during early afternoon and early morning respectively over land. Over the oceans, the diurnal effect is considered minimal because of the small diurnal change of seawater temperatures. Along coasts and lakeshores, pressure differences created by heating and cool-ing set up what we know as sea and land breezes.