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have presented significant maintenance and reliability problems according to the forecast and maintenance staffs at WSFO Denver and the Central Region Headquarters. Termed "experimentally operational," these 14 installations, which were activated in 1975, were not yet commissioned. No use of the data from them was being made by WSFO Denver prior to or during the flood. They had concluded that the maintenance and reliability problems with these test systems made them unusable. The electronic tech- nicians at Denver have continued to monitor the read-outs daily, for mainte- nance purposes. There were initial problems with the SMS-l satellite data relay systems. Since transmission through SMS-2 began in March, 1975, the primary problem with these systems, according to the Equipment Program Officer at Denver, was in the Data Collection Platform Radio Sets (DCPRS). The maintenance problems with the 14 sets were recognized by NWS in 1975 and new sets will replace these test sets by the end of 1976. One of the AHOS/S units was installed at Drake in the Big Thompson Canyon. The reports from this rain gage indicate that it was operating and reporting on schedule until Thursday, July 29. On that date, the reading dropped from the previous reported accumulation of 5.00 inches to 1.00-inch, indicating that either the equipment had malfunctioned or the gage had been partially emptied. The 1.00-inch reading continued to be reported until the gage was destroyed by the flood shortly after its last scheduled report was made at 7:00 p.m. on July 31. Three of the AHOS/S rain gage sites (Drake, Rustic, and Fort Collins) have people under contract to periodically empty the rain gages and mail in the recorder charts. The Meteorologist-in-Charge at WSFO Denver indicated they were going on the assumption that the test system would work and did not ask these people to act as back-up observers for a test system. Reports from public, spotter networks, local and state officials--These reports are vital to an effective warning program. Radar and satellite systems give indications, but do not tell exactly, what weather is occurring. Most severe local storms are too small in horizontal extent to be picked up by the standard surface observing networks. Therefore, surface observing networks, satellites, and radars must be reinforced by on-the-spot cooperative observers if we are to give the precision and accuracy to warnings needed to make them useful and credible to the public. There were many such potential observers in the Big Thompson Canyon early in the evening of July 31. Numerous eyewitness accounts of downpours and flood- ing were later reported in newspapers. Not one of these reports reached the forecaster in WSFO Denver in time to refine his warning and reflect the disastrous events in the canyon. Shortly after 8:00 p.m., law enforcement dispatchers had indications of rocks blocking a section of U.S. Highway 34, but this information was not given to WSFO Denver until about 9:30 p.m. At about 10:00 p.m. similar information was put on NOAA Weather Wire by 10