The 850mb level is also important in winter for predicting precipitation types like freezing rain. If the temperatures above the surface in winter are above freezing, while temperatures at the surface are below freezing, it is possible to have freezing rain. The 500mb level represents conditions in the middle of the atmosphere. Low pressure features are also very easily identified in this region. They are often termed troughs in the upper levels.
Troughs represent dips in the contours that are pushed toward the equator.
The 500mb level is usually where the middle of a cyclone is located. Cold air at this level, ahead of the trough, but above the warm moist air creates a conditionally unstable atmosphere. The 250mb level is used to study jet streams . Contouring isotachs at this level is more valuable than streamlining, as this well help locate special features like the jet streak. In addition, this level is also important in analyzing if surface air will rise.