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TEXARC 1994 and 1995 results suggest the importance of when and where the various microphysical processes take place within the cloud and when and where the seeding takes place that is intended to alter these processes. Both the Rosenfeld/Woodley conceptual model and these results suggest that, when seeding for rain enhancement, it is crucial to produce glaciation artificially within the vigorous supercooled updraft region of the cloud. It is in this region that large artificially nucleated precipitation- sized particles can be grown most efficiently. Accomplishing this through seeding requires great care in the placement of the nucleant either in the updraft directly near cloud top or in the strong inflow region at cloud base in well-developed convective systems (Rosenfeld and Woodley, 1997). The TEXARC research effort continued in 1998 under the auspices of the TNRCC. The core-effort in 1998 involved the use of a cloud physics aircraft (a Piper Cheyenne turbo prop) in the period from 6 through 27 September 1998 to study the effects of seeding on Texas supercooled clouds. Weather Modification, Inc. in Fargo, North Dakota supplied the aircraft. Prior to its arrival in Texas it was being used in Mexico in a hygroscopic seeding experiment under the direction of the National Center for Atmospheric Research in Boulder, Colorado. During TEXARC 1998 there were 15 flights on 13 days with the expenditure of 33.87 flight hours by the Cheyenne cloud physics aircraft. There were 5 flights on 5 days with the qualification of 21 cloud physics units. The initial motivation for the research was the testing of two silver iodide (AgI) flares that had been tested previously in the laboratory. The first flare was the TB1 formulation, which acts by contact nucleation and has been available to the weather modification community for many years. The second flare formulation was given the BF1 designation after its developer, Dr. William Finnegan, who has assisted Texas with its flare development. The BF1 flare acts by condensation freezing. These tests were part of a program that developed a seeding flare for Texas. The BF1 flare was found to outperform the TB1 flare in terms of the rapidity of induced glaciation and the total number of generated ice particles, although the measured differences in the clouds were small. This is consistent with the results of laboratory testing. Both flares produced similar changes in the clouds relative to those receiving no treatment. The second motivation for the tests was to learn more about how seeding affects the draft and microphysical structure of the clouds. This was done in the context of the cold-cloud conceptual seeding model, which had been under development for many years. The cloud physics aircraft was equipped with reverse-flow temperature and dew point probes to make atmospheric soundings close in time and space to the intended cloud studies. It had a Ball variometer for the inference of cloud drafts. The PMS probes on the Texas cloud physics aircraft were used to measure droplet and particle sizes in the range from 3 to 800 microns. The FSSP probe was used to document the development of the cloud droplet spectrum with height, beginning at and about 100 meters above cloud base. The 2DC probe was used to document the habit, concentrations and sizes of the cloud hydrometeors before and after cloud treatment as the aircraft flew perpendicular to the seeding curtain. The aircraft was equipped also to measure total aerosols and CCN using PCASP and CCN instrumentation, respectively. The conclusions made were that seeding appears to result in the production of graupel ice in invigorated updraft regions with a concomitant decrease in the cloud water as required by the conceptual model. This gives greater impetus for the use of AgI seeding for rain enhancement (Woodley and Rosenfeld, 2000). An example of what is now called “secondary seeding” comes from TEXARC during the September 1998 cloud physics program when randomized microphysical case studies were qualified (Woodley and Rosenfeld, 2000). The subject cloud was qualified at 18:33 CDT on 22 September 1998 and treated with nine, 20-gm, BF-1, AgI flares as determined by the randomized treatment decision. Secondary seeding is not unique to seeded clouds nor is it a rare event. Rosenfeld and Woodley (1997) discuss a case, showing that “clouds that existed in a clustered environment and had ingested embryos from decayed clouds contained large raindrops on the initial pass through active cloud towers. 12