LINES:

For this class of graphics, solid black lines represent isohypses which are defined as lines of constant geopotential height. Here the geopotential height is for the 850 mb atmospheric pressure level. The isohypses are drawn in thirty meter increments with the largest and smallest values also labeled. Thin brown lines represent lines of equal relative humidity (RH) and are labeled in regions with RH larger than 70 % with the largest and smallest values also labeled. The intervals may be different depending on the product you are viewing therefore it is important to look at the line interval legend at the bottom right of the plot.

COLORS:

Background color represents the RH at 850 mb in percent. The color-bar located at the bottom identifies the RH for each shading of color with RED shades indicating areas containing more moisture.

WHY IS THIS IMPORTANT?

Relative humidity maps enable forecasters to determine how much moisture is associated with a particular air mass. Regions with higher RHs (RED) have the moisture needed to develop and sustain clouds and precipitation, although RH itself is NOT the only factor and other conditions must be present. RH only indicates whether the air mass has enough moisture that there is a possibility of clouds and precipitation to form.