When the upper atmosphere is very dry, contrails form at very cold temperatures, the ice crystals sublimate very rapidly, and the contrail does not persist. When the relative humidity is fairly high, the contrails can form at relatively higher temperatures, and they will persist, broaden, and perhaps become visible in meteorological satellite images. They can be identified as contrails because they are very straight and occasionally criss-cross. Naturally forming cirrus cloud bands are usually broader, thicker, and somewhat parallel. The newly formed contrails such as those in southern Indiana are narrow, and well defined.
Older contrails seen in Illinois are broader and more diffuse.
Note the well defined shadows cast onto the surface from the contrails in southern Indiana. The large distance between the clouds and their shadows in this mid-morning image indicates that the contrails are at very high altitudes. Another factor is that the resolution of GOES infrared is 4 km , compared to 1 km in this visible image. There were no contrails evident to the north or south of a narrow zone probably because there was insufficient moisture at high altitudes. GOES water vapor imagery is useful for estimating high level moisture.