What causes variations in altimeter settings between weather reporting points?

Variations in altimeter settings between weather reporting points are primarily caused by unequal heating of the Earth's surface. This phenomenon affects atmospheric pressure, which is what altimeters measure to determine altitude.

When the Earth's surface is heated unevenly by the sun, it leads to differences in air temperature and pressure in various areas. Warm air tends to rise, creating areas of lower pressure, while cooler air leads to higher pressure. Since altimeters are calibrated to read pressure as altitude, these variations in atmospheric pressure will result in different altimeter settings at different locations.

Understanding this concept is crucial for pilots, as they must adjust their altimeter settings based on the local atmospheric pressure to maintain accurate altitude readings during flight.