The AFGL instrumented MC-130E sampled thin cirrus clouds on 3,4, and 5 February 1979. In some cases, there was no visible cirrus, but some particles were detected. During this period, the upper air pattern was dominated by southwest to northeast flow, while two surface systems moved from north to south. The first of these left thin cirrus in eastern New Mexico; the second pushed south to the Gulf of Mexico, leaving the cirrus studied on the previous two flights. Most of the particles observed were less than 100 microns. As a rule, the opacity of the cirrus seemed related more closely to the density of particles in the 20- to 200-micro range. On examination the form factor appeared to be higher (indicating more consistent sized particles) in cirrus of nonfrontal origin than in cirrus associated with strong surface weather systems. This report is the last in a series of cirrus particle distribution studies.