We've guessed that you're not using a client that supports colored tables and have tried to compensate. Strong ridges are accompanied by warm and dry weather conditions at the surface. The purple line denotes the ridge axis.
Temperatures decrease with color from light blue to purple.
A ridge is located from Texas into Montana and is indicated by the bulge in the geopotential height field . This is the upper level extension of a surface high pressure center , which is why ridges are also called upper level highs. Notice the relatively warm temperatures associated with the ridge. This is caused by the northward transport of warmer air in the lower troposphere. Credits and Acknowledgments for WW2010.