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remote meteorological sites and the location of the project rawinsonde site are also indicated in Figure 1. OPERATIONAL PLAN The Pilot Project was designed to have 50 p1ercent of the experimental days selected at random to be seeded and 50 percent non-sleeded. A block randomization scheme was devised for the seeding of experimental days for the duration of the project prior to the start of the operational program in December 1970. Each experimental day ran- dom seeding decision was accessed through a special program in the time-share computer service. An experimental d~y constituted a 24-hour period from 1100 to 1100 MST. Any 3-hour (12-hour the firist season) or greater portion of the 24-hour period meeting the experimental meteorological criteria w~~ld be considered as an operational period using the seeding decis~on for that 24-hour experimental day. The experimental mete- orological criteria that must simultaneously occur over the target area within a time period of 3 hours (12 hours the first season) or greater and the changes that occurred in these criteria during the five operating seasons are as follows: 1) Precipitation of 0.01 inch or gr.eater is forecast for anywhere in the tar- get area during the 1100 to 1100 MST,period. Effective 1 October 1971 changed to: I-a) Precipitation of 0.01 inch or greater is forecast for one or more of the following gages in the project target areas during the 1100 to 1100 MST period when Condition 2 and 3 (below) are met: a) KH-l - Lemon Park b) JK-l Northfork Sand Creek (added effective 8 November 1972) c) KO-3 - Wolf Creek West d) MO-l - Nipple Mountain (added effective 8 November 1972) e) NP-3 - Castle Creek o 2) 500 mb temperature of -23 C or warmer is forecast to exist over the pro- ject area at least 12 hours during the 1100 to 1100 MST period. Effective 17 April 1971 changed to: 2-a) Cloud-top temperature or, in the absence of this datum, 500 mb temp- o erature of -23 C or warmer is forecast to exist over the Project target areas at least 12 hours during the 1100 to 1100 MST period. Effective 1 October 1971 changed to: 2b) Cloud-top temperature or, in the absence of this datum, 500 mb temp- erature of -230C or warmer is forecast to exist over the Project target areas at least 3 hours during the 1100 to 1100 MST period. The operational criteria of cloud- top temperature shall be applied to the highest observed clouds including cirrus. Effective 21 January 1972 changed to: 2c) Cloud-top temperature or, in the absence of this datum, 500 mb temp- erature of -230C or warmer is forecast to exist over the Project target areas at least 3 hours during the 1100 to 1100 MST p.eriod. The operational criteria of cloud- top temperature shall be applied to the low.er precipitation-producing cloud mass. In those ~. ses where upper clouds are present, with a substantial clear air layer between th tops of the lpwer layer and the base of the upper layer, the cloud-top temperatur of the uppe^rcloud layer will not be used in application of the cloud- top tempera ure criterion. 3