Many of these occur along the poleward edge of persistent cirrus shields or moisture seen in the IR or WV imagery. There are often satellite signatures that suggest the presence of CAT, although the altitude cannot be determined accurately. One of the indications is the presence of well-defined cirrus bands oriented nearly perpendicular to the upper winds. The most intense turbulence is related to wide, thick bands easily seen in IR imagery or visible . The bands occur in the presence of strong vertical and horizontal wind shears below the jet.
Winds often show pronounced backing with height .
Moderate CAT was observed through the day along the jet, and in the right front quadrant. In these situations, we frequently see progressive darkening in the WV imagery, such as that which occurred on 11 January 1996. The darkening is caused by strong subsidence within a tropopause fold, induced by upper level convergence. A cross section through the leading edge of the dry zone shows the structure across the trough axis and jet stream on the morning of 11 January. The isentropes slope downward as they approach the north Texas area, where the dry slot is present.