1. Data is tabulated for each precipitation gage based on the "1999 Water Year" which begins Oct. 1st, 1998 and ends on Sep. 30th, 1999. Each data page represents one gage, and lists the daily precipitation totals, the monthly totals, the cumulative rainfall by month, the maximum daily value each month, and the number of days with rain. The data pages are arranged in ascending order by sensor ID number.

2. The unit of measurement for daily precipitation totals provided in this report is inches. Annual totals are also provided in millimeters.

3. An index of gage names, numbers, locations, and other descriptors is included as Table I.

4. All of the data in this report has been reviewed and/or edited in an attempt to provide the most accurate data possible. Where possible, inaccurate data is flagged with a footnote describing the time the gage was down, the cumulative rainfall count in millimeters at the beginning and end of the down period, whether or not rain fell during that time, and whether or not monthly and annual totals were affected. For example, a footnote might read " Gage down from 2/12 03:40 (92) through 2/14 13:30 (94) due to lightning strike; rainfall assigned to 2/13", where the values in parentheses are the beginning and end rainfall counts in millimeters.

5. Snow gages were in service during Water-Year 1999. They consist of a 4' tube mounted vertically to the tipping-bucket funnel. Consequently, gages above approximately 5,000 feet will show meltwater following the colder winter events.

6. Table II lists the sensors installed in the FCDMC ALERT System during Water Year 1999 and their installation dates. Table III lists the annual rainfall total for each gage, sorted by decreasing amount, along with Water-Year totals for 1998, 1997, and 1996. Table III can also be used as a quick reference to determine which gages were installed during the Water Year, which had incomplete records, and which had estimated totals. In the case of estimated totals, one or more daily totals were calculated using either the Isohyetal or Thiessen polygon methods applied to nearby rain stations.

7. Additional and/or more detailed sensor data in hard copy or computer disk format is available for the gages listed in this report. Contact the Flood Control District, Engineering Division, Flood Warning/Water Quality Branch at (602) 506-8701.

8. Note on data compilation: Nearly all automatic rain gages in this network measure rainfall depth in 1mm increments. The base station computer which collects the data uses the equation 1mm = 1/25.4 or 0.03937 inches to convert millimeters to inches. As a result, daily totals may sum to a slightly different total than the reported monthly total (which is more accurate than the sum of the daily totals) because of rounding errors. In the same way, the annual totals reported in Table III may not match exactly the sum of the monthly totals, but can be considered more accurate.

9. Note on the accuracy of monthly and annual totals: Because automatic ALERT gages are designed for flood warning applications, there is some inherent error associated with their use in maintaining accurate long-term records. The majority of tipping buckets collect rainfall in 1mm increments before sending a signal and dumping the accumulated rainfall. Because evaporation often dries the bucket between storms, the measurement error averages out to be 0.05 mm (0.02 in) times the number of rainfall events during the period of interest (month or year). It is also conceivable that during times of low evaporation and/or short times between storms that the bucket could be partially or nearly full at the start of a rainstorm. Other errors can be introduced by the effects of gage height, calibration errors, and the physical environment (trees, buildings, wind patterns) near the gage.