Graph — Psychrometric

These are sweeping parabolic curves. Each curve represents a percentage of saturation (0% to 100%). The 100% RH line is the Saturation Line . Air cannot hold more moisture beyond this line; it will start to condense (dew, fog, rain).

These are straight vertical lines (or horizontal, depending on the chart's orientation). They represent the sensible heat level of the air—the heat you can feel. psychrometric graph

The term comes from the Greek psukhros (cold) and metron (measure). While it measures "cold," its real power lies in measuring change. These are sweeping parabolic curves

To read the chart, you must identify its seven fundamental components. Most charts are plotted with (the temperature your thermometer reads) on the horizontal axis. Air cannot hold more moisture beyond this line;

Meteorologists use derived psychrometric principles to predict fog formation. If the temperature drops to the dew point (intersects the saturation curve on the graph), fog or dew will form.